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Title: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on March 19, 2018, 11:58:15 am
I have a 2x10" x CD box.  The CD is a JBL 2426-J.  I constructed a 4th order L.R. passive crossover at 1,300hz for use inside the box.  The crossover works, but when strong low fundamentals are introduced, I get clipping/buzzing from the CD.  This happens even at low volume levels when I'm not pushing the amp hard by any means.

I thought I had read somewhere while designing this that a cap may be needed between the CD and its connection to negative.  This is to prevent lows from backing up into the CD from the common connection with the low negative on the low side of the X-over.  Doesn't seem to make sense, but... Any ideas?
The high side negative is obviously common with the low side negative of the X-over.

Secondly, could I put another cap between the end of the high side crossover positive and the positive input to the CD as additional protection, or will that mess with the x-over?
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Chris Grimshaw on March 19, 2018, 12:08:21 pm
If you're getting enough low-frequency signal into the compression driver to cause problems, there's something wrong with your crossover.

A 4th order crossover at 1.3kHz would be of the order of 100dB down at 80Hz. Given that 3dB is a doubling of power, you'd need to put 8.5x10^9 watts into the system to put 1w of signal into the compression driver at 80Hz.

Even then, I expect 1w would be dealt with just fine. 10w would probably present issues, so now you need 85 billion watts.

I suspect that you don't have a fleet of large power stations all dedicated to your amplifier, so the only sensible conclusion (IMO) is that the crossover is faulty.

If you could take some photos of the crossover you've built and post them here, I'd be happy to take a look.

Chris

PS - check the voicecoil alignment.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on March 19, 2018, 12:24:13 pm
Chris
Hi Chris, I doubt you will remember but you and a few others were helping me with my design.  I got a tour and went on the road for a few months and am just getting around to finishing it. 

Here is a drawing.  the 20uF was suggested, but I see no reason for it because when that lead is live, the x-over would be switched out (for use with active outboard).
There is also no L-Pad in the real thing.

Maybe I need to triple-check my wiring.  Although I was pretty thorough.

I think VC alignment is fine because the setup works great when I use the outboard active x-over in the amp.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Ivan Beaver on March 19, 2018, 12:42:48 pm
I have a 2x10" x CD box.  The CD is a JBL 2426-J.  I constructed a 4th order L.R. passive crossover at 1,300hz for use inside the box.  The crossover works, but when strong low fundamentals are introduced, I get clipping/buzzing from the CD.  This happens even at low volume levels when I'm not pushing the amp hard by any means.

I thought I had read somewhere while designing this that a cap may be needed between the CD and its connection to negative.  This is to prevent lows from backing up into the CD from the common connection with the low negative on the low side of the X-over.  Doesn't seem to make sense, but... Any ideas?
The high side negative is obviously common with the low side negative of the X-over.

Secondly, could I put another cap between the end of the high side crossover positive and the positive input to the CD as additional protection, or will that mess with the x-over?
It does not matter if the xover is in "pos" or "com" side of the driver.  It will work either way., as long as it is wired properly.

Adding another cap on the neg side would actually just add another pole to the filter network, making it 30dB (assuming the proper values were used).

I suspect a wiring error someplace.

The problem with using "calculated values" in a xover is that they assume the freq response is flat (most of the time it is not flat), and they assume that the impedance is constant, which it is not.

So the result is something other than the simple calculated response.

Getting a proper passive xover is a bit more work, than the basic formulas.

But if you used the basic values, you should not be getting lows into the HF.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on March 19, 2018, 12:53:35 pm
For some reason, this forum will not allow me to post a pic of the actual build.  (size is lower than 512KB, etc.) 
Anyway, It looks like I need to triple-dog check the wiring.
The 'active' sounds better.  I'm guessing the only way to really build a passive to be accurate would be to measure and tweak with real-world response. e.g. the driver impedance is not the stated value outside the frequency at which it was measured... But if I can get into the ballpark, it will be fine. 
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Scott Holtzman on March 19, 2018, 01:00:36 pm
For some reason, this forum will not allow me to post a pic of the actual build.  (size is lower than 512KB, etc.) 
Anyway, It looks like I need to triple-dog check the wiring.
The 'active' sounds better.  I'm guessing the only way to really build a passive to be accurate would be to measure and tweak with real-world response. e.g. the driver impedance is not the stated value outside the frequency at which it was measured... But if I can get into the ballpark, it will be fine.

Post the picture on a photo sharing site then put the link here.

Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on March 19, 2018, 01:04:31 pm
Post the ... link here.
https://photos.app.goo.gl/cbR8axs4xt4xXCs92
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Stu McDoniel on March 19, 2018, 01:05:55 pm
For some reason, this forum will not allow me to post a pic of the actual build.  (size is lower than 512KB, etc.) 
Anyway, It looks like I need to triple-dog check the wiring.
The 'active' sounds better.  I'm guessing the only way to really build a passive to be accurate would be to measure and tweak with real-world response. e.g. the driver impedance is not the stated value outside the frequency at which it was measured... But if I can get into the ballpark, it will be fine.
Sounds like a wiring problem
Put a loudspeaker on the high connection and run some pink noise through it.
Sine wave sweep.
If you even suspect an issue disconnect and dont trash your CD diaphragm until you get it worked out.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Don T. Williams on March 19, 2018, 01:08:38 pm
Jeff, if I'm understanding the switch, it allows you to biamp the speaker system and by-pass the internal passive cross-over.  If this the case, the suggested cap is there to keep DC voltage (and some LF) out of the HF driver/horn to protect the speaker system (a 6 db/octave high-pass filter).  EV did this on their bi-amp only X-array products.  I'll tell you it saved more than one driver in my system.  As Ivan stated, if this is added to the existing passive cross-over it will add another pole to the filter and change how the cross-over filters work.  And, as Chris said, it IS NOT needed if the passive cross-over is wired & working correctly.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on March 19, 2018, 01:20:22 pm
Sounds like a wiring problem
Put a loudspeaker on the high connection... dont trash your CD diaphragm until you get it worked out.
Good call.  A regular driver will still give me enough to know if I have it working.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on March 19, 2018, 01:25:10 pm
Jeff, if I'm understanding the switch, it allows you to biamp the speaker system and by-pass the internal passive cross-over. 
Yes.
If this the case, the suggested cap is there to keep DC voltage (and some LF) out of the HF driver/horn to protect the speaker system (a 6 db/octave high-pass filter).  EV did this on their bi-amp only X-array products.  I'll tell you it saved more than one driver in my system.
Makes sense, so I'll just leave that in place.  It's a high value because it is just for safety, to keep DC or VLF weirdness out, not to shape the sound.  Got it.
As Ivan stated, if this is added to the existing passive cross-over it will add another pole to the filter and change how the cross-over filters work.  And, as Chris said, it IS NOT needed if the passive cross-over is wired & working correctly.
so to do it 'correctly,' I'd need to add another inductor as well and make it a 6th order LR.  But yes, point taken.  If it was wired right it should already work fine without adding another filter.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Scott Holtzman on March 19, 2018, 01:49:18 pm
Yes.Makes sense, so I'll just leave that in place.  It's a high value because it is just for safety, to keep DC or VLF weirdness out, not to shape the sound.  Got it.so to do it 'correctly,' I'd need to add another inductor as well and make it a 6th order LR.  But yes, point taken.  If it was wired right it should already work fine without adding another filter.

The additional pole will cause another "trip around the phase wheel" and the associated delay added to the total network delay. 
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: David Morison on March 20, 2018, 12:47:43 pm
Jeff, the component values in that table look a lot like they've come out of a generic calculator, would that be right?

<EDIT> I just googled "LR crossover calculator" and took the first result, and it gave me exactly the diagram you've posted - so I guess that answers that.

So, they definitely do not take account of the fact that the impedance of the driver is not a constant 16Ω at all frequencies.

Passive Crossovers work by interacting with the driver's impedance, so if the driver impedance is not flat at 16Ω then the attenuation will not be the expected 24dB/oct.

Specifically, the higher the driver impedance, the less the attenuation from a given passive filter.

So, looking at the impedance curve on the spec sheet for the 2426 (copy below), there's a big (as in 4 times the nominal) impedance peak around 420Hz and a smaller one at ~1k2 ish. (The exact frequency and height of these peaks will vary depending on what horn you have it on, so you do need to take an impedance sweep of your driver & horn combination before starting to work out component values.)

Having a bunch more 400-odd Hz content than you expected hitting your driver could very easily cause the observed increase in distortion/noise, IMO.

One way to flatten those impedance peaks is to use what's called a Series Notch Filter (http://www.speakerbuilding.com/content/1041/). I know some sites suggest that with higher order crossovers there's less need for these, but if the impedance peaks are as high on your horn as the spec sheet shows, I'd seriously consider one.

HTH,
David.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on March 20, 2018, 07:13:07 pm
So - you guys were right, it was a wiring issue.  The crossover now works as designed.  There is no rattle or distortion.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on March 20, 2018, 07:15:02 pm
Jeff, the component values in that table look a lot like they've come out of a generic calculator, would that be right?

<EDIT> I just googled "LR crossover calculator" and took the first result, and it gave me exactly the diagram you've posted - so I guess that answers that.

So, they definitely do not take account of the fact that the impedance of the driver is not a constant 16Ω at all frequencies.

Passive Crossovers work by interacting with the driver's impedance, so if the driver impedance is not flat at 16Ω then the attenuation will not be the expected 24dB/oct.

Specifically, the higher the driver impedance, the less the attenuation from a given passive filter.

So, looking at the impedance curve on the spec sheet for the 2426 (copy below), there's a big (as in 4 times the nominal) impedance peak around 420Hz and a smaller one at ~1k2 ish. (The exact frequency and height of these peaks will vary depending on what horn you have it on, so you do need to take an impedance sweep of your driver & horn combination before starting to work out component values.)

Having a bunch more 400-odd Hz content than you expected hitting your driver could very easily cause the observed increase in distortion/noise, IMO.

One way to flatten those impedance peaks is to use what's called a Series Notch Filter (http://www.speakerbuilding.com/content/1041/). I know some sites suggest that with higher order crossovers there's less need for these, but if the impedance peaks are as high on your horn as the spec sheet shows, I'd seriously consider one.
David, Yes, you are right, I used a calculator.  I'm aware of varying resistance levels affecting crossover points and phasing. I looked at the curve before I made it and kinda guessed if I was over about 1k2 I'd be mostly okay.  Old school passive crossovers aren't really ideal anyway.   Ideally, I will be using the active crossover in my amp.  But for applications where I'm using a single 2-channel amp to bi-amp this box, along with a low freq. cab I'll use this.  I can still use EQ in the amp regardless. 
I have read about notch filters to even out impedance.  It'd be easy to add one.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Ivan Beaver on March 20, 2018, 07:38:11 pm
So - you guys were right, it was a wiring issue.  The crossover now works as designed.  There is no rattle or distortion.
Hopefully you caught it before any damage occurred.

Anybody who says they never made a wiring error, is either lying or hasn't done it long enough.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Scott Holtzman on March 20, 2018, 07:43:15 pm
David, Yes, you are right, I used a calculator.  I'm aware of varying resistance levels affecting crossover points and phasing.

I am glad you found the wiring error, I tried like crazy to find it in the picture for you.

To truly understand though you need to stop using the word resistance.  It's impedance.  This is an AC network not DC.  You are building a frequency dividing network and part of the math is figuring out how it will perform at the extents.  That includes component tolerances and frequency curves. 

This multi-series analysis is called the Monte Carlo Method.  You will find some good spreadsheet templates to help with the task if you google that phrase (is it OK to use Google as a verb?0.

Good luck
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Art Welter on March 20, 2018, 08:07:23 pm
So - you guys were right, it was a wiring issue.  The crossover now works as designed.  There is no rattle or distortion.
Jeff,

Be glad you are using titanium rather than aluminum diaphragms!

Measure the raw response of the horn/driver, compare the response of it with the crossover you built- if it looks like 24 dB per octave below the frequency you intended, then you might say it "works as designed".
Until then, stick with "there is no rattle" ;^).

Art




Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on March 20, 2018, 09:27:41 pm
Measure the raw response of the horn/driver, compare the response of it with the crossover you built- if it looks like 24 dB per octave below the frequency you intended, then you might say it "works as designed".
Until then, stick with "there is no rattle" ;^).
Very true!  :) I think for now its that mostly highs come out the high thingie and more-or-less lows come out the low thingies and nothing blows up we're good.  This project has given a new appreciation for the value of active X-overs.
I'll set it up for testing at some point and mess with EQ, but that's a project for another day.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on March 20, 2018, 09:33:20 pm
Hopefully you caught it before any damage occurred.
Anybody who says they never made a wiring error, is either lying or hasn't done it long enough.
I think I did.  I wasn't playing loud, just making sure things worked when I caught it.  As Art said, good thing for Titanium.  I've blown stuff up doing FAR less. 
It was a simple error, but yeah, even with double checks, sometimes I screw up :)
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on March 20, 2018, 09:40:29 pm
I am glad you found the wiring error, I tried like crazy to find it in the picture for you.

To truly understand though you need to stop using the word resistance.  It's impedance.  This is an AC network not DC.  You are building a frequency dividing network and part of the math is figuring out how it will perform at the extents.  That includes component tolerances and frequency curves. 

This multi-series analysis is called the Monte Carlo Method.  You will find some good spreadsheet templates to help with the task if you google that phrase (is it OK to use Google as a verb?0.

Good luck
Look closely.  Do you see how the last inductor from the low side is connected to the output of the first cap in the high side?  Soon as I saw it, I promised myself not to drink beer while wiring again.  DOH  ;)
Yes - impedance.  Resistance varies with frequency...
As far as Monte Carlo - variables like component tolerances, specs vs. real and so on... Without lots of fancy equipment, there's a certain amount of trial and error isn't there?  I have calibrated mic and software to analyze the finished product, but the design is kind of guessing and refining, isn't it?

Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Scott Holtzman on March 20, 2018, 09:48:12 pm
Look closely.  Do you see how the last inductor from the low side is connected to the output of the first cap in the high side?  Soon as I saw it, I promised myself not to drink beer while wiring again.  DOH  ;)
Yes - impedance.  Resistance varies with frequency...
As far as Monte Carlo - variables like component tolerances, specs vs. real and so on... Without lots of fancy equipment, there's a certain amount of trial and error isn't there?  I have calibrated mic and software to analyze the finished product, but the design is kind of guessing and refining, isn't it?

No it's just math. Resistors at 10% caps, whatever they are.  The analysis will wrangle those series for you. 

The drivers should have published impedance curves too.  You do need a test rig for that.

 
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Chris Grimshaw on March 21, 2018, 05:17:13 am
I have calibrated mic and software to analyze the finished product, but the design is kind of guessing and refining, isn't it?

To some extent, yes. Simulations can help, though. I've just completed my own passive crossover design for a pair of small speakers, where bi-amping didn't make sense. 18Sound 6ND430 and a Das M3 compression driver.

What I did was build the boxes and measure the drivers (impedance and frequency response) in those boxes. Then I fired up XSim and played around until I got something good, that also met the criteria of keeping the HF driver safe and the off-axis response reasonably smooth.

You can see what happened here: http://www.diyaudio.com/forums/pa-systems/271132-chris661s-pa-system-thread-9.html#post5359495

Chris
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Art Welter on March 21, 2018, 01:51:44 pm
As far as Monte Carlo - variables like component tolerances, specs vs. real and so on... Without lots of fancy equipment, there's a certain amount of trial and error isn't there?  I have calibrated mic and software to analyze the finished product, but the design is kind of guessing and refining, isn't it?
Using a program as Chris does like XSim will get you close, but the amount of trial and error after is still pretty uncertain, and can't be determined without measurement.
You may be able to change only one or two values and get "close enough", but the more poles you add, the more complicated the interactions.
Both frequency response and impedance measurements are needed- "flat" response might end up with a narrow band impedance dip that is problematic with a certain amplifier (damn it..)...

Art



 
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Chris Grimshaw on March 22, 2018, 04:46:59 am
Using a program as Chris does like XSim will get you close, but the amount of trial and error after is still pretty uncertain, and can't be determined without measurement.

Art

Very true. XSim and REW measurements didn't quite see eye-to-eye, despite my best efforts. It got me close enough that a little trial and error got me where I wanted to go, though.

Chris
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Ivan Beaver on March 22, 2018, 07:31:27 am
Using a program as Chris does like XSim will get you close, but the amount of trial and error after is still pretty uncertain, and can't be determined without measurement.
You may be able to change only one or two values and get "close enough", but the more poles you add, the more complicated the interactions.
Both frequency response and impedance measurements are needed- "flat" response might end up with a narrow band impedance dip that is problematic with a certain amplifier (damn it..)...

Art
Agreed, impedance dips are real easy to have.

Or part of the impedance curve in which the phase of the impedance is to inductive or capacitive, putting additional strain on the amp.

There are a number of things that you must pay attention to, or you can put a strain on various parts of the system.

As usual, there is a lot more than simple amplitude to be concerned with.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on March 22, 2018, 10:24:30 am
Darn you guys, LOL always doing things correctly...  :)

I checked a couple vids on X-Sim.  I've worked on preamps with LTSPICE, so it looks pretty easy.  I'm also pretty good with REW (which I was going to use to measure anyway) and, like the guy in the vid, I have boxes of wire, caps, resistors, etc.  I've also thought of adding an L-Pad, and maybe an impedance smoother.  Why not do it correctly...  It'll be interesting to see how far off the online calc is.  This is just the top end of my bass guitar rig, but why not make it optimal.
(As an aside, this is really silly.  For my last three gigs, one of which was a semi-known touring band - it's all been in-ear monitoring. i.e. no backline at all.  I don't even bring speakers or amps.  Even in the clubs, noisemakers on stage are becoming very passe for bands who actually want to sound good.  The new gig I have is also with IEM's only. This is kinda for my own amusement I guess.)

One thing I saw which raised concern.  In the vid, the guy had his speaker set up in the garage with his mic a meter away.  I know this would result in a horribly skewed response with a sub but will room variances really not be an issue with a mid/high?  Was thinking I had to wait for a nice day and a friend with a big backyard to measure accurately.  I'd love it if I can measure here at home.

Another thing is finding the driver simulations/measurements for X-Sim. The gentleman seemed to have a couple on dropbox but not what I need. Anyone know where I can find them for an Eminence Delta 10A and a JBL 2426?  The horn makes a huge difference too.  In the interests of space, I had to use a non-optimal one.  Maybe I should just measure it myself outside the box.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Mark Wilkinson on March 22, 2018, 10:48:45 am
The best indoor measurement technique I've found, is to put both speaker and mic on a hard surface floor, away from other objects if possible.
1 meter works.  Measurements are of course more suspect the lower they go, but I'm often pleasantly surprised how well the on-the-floor-indoor hold up above 100Hz, compared to outdoors.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on March 23, 2018, 06:31:14 am
I'm often pleasantly surprised how well the on-the-floor-indoor hold up above 100Hz, compared to outdoors.
Have you compared?  How much difference do you get?  Because yeah, you're right - with lows, measuring indoors is completely unusable, unless it's anechoic somehow...
How far away from walls and objects was the speaker when you measured?  My place is pretty small.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Mark Wilkinson on March 23, 2018, 01:40:23 pm
Have you compared?  How much difference do you get?  Because yeah, you're right - with lows, measuring indoors is completely unusable, unless it's anechoic somehow...
How far away from walls and objects was the speaker when you measured?  My place is pretty small.

Yep, made lot's of comparisons.  Below is a mid section box, green trace is on the floor, blue is outside.  1/6 oct.
By outside, I mean off a deck putting speaker 15ft off ground  pointing away from house.  Mic is on a boom 9ft out from speaker.

I find the floor method works with stuff fairly nearby.  Just get in the center of the room if you can. 
Oh, nearby drivers, even shorted out....are often worse than fixed objects.

I lay speakers on their side, and block the back side up to have speaker point perpendicular to mic on floor.  Makes for good on-axis.
It pays to just move mic around to make sure measurements aren't too mic position sensitive, needing averaging.

FWIW, with REW, I'm willing to eq per floor measurements, using frequency dependent widowing of FDW 5 or 6. 
Any finer resolution is probably (but not necessarily) letting too much room in, or too mic position dependent.

Hope this helps!
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on March 23, 2018, 02:36:12 pm
I lay speakers on their side, and block the back side up to have speaker point perpendicular to mic on floor.  Makes for good on-axis.
It pays to just move mic around to make sure measurements aren't too mic position sensitive, needing averaging.
Wow, those are a lot closer than I would have thought.  Totally close enough for my purpose.
When you say that you prop it on its back, I don't understand.  Perpendicular  to the mic?  You want the mic pointing directly at the speaker...
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Tim McCulloch on March 23, 2018, 03:48:17 pm
Jeff - we have a measurement forum here among the various parts of the LAB.  Measurement-specific questions would probably get more/faster answers there.

There are measurement techniques and stimuli that allow you to "window" a measurement but those become less effective/affect the quality of data as the frequency gets low.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Mark Wilkinson on March 23, 2018, 04:21:36 pm
Wow, those are a lot closer than I would have thought.  Totally close enough for my purpose.
When you say that you prop it on its back, I don't understand.  Perpendicular  to the mic?  You want the mic pointing directly at the speaker...

Maybe a picture helps explain what I was trying to say ...

2nd Tim's suggestion, you'll get more replies...and likely from folks with more experience than me !
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on March 23, 2018, 08:04:23 pm
Maybe a picture helps explain what I was trying to say ...

2nd Tim's suggestion, you'll get more replies...and likely from folks with more experience than me !
Oh wow. You weren't kidding about putting it on the floor!  I'm amazed it gets nearly the response as outdoors!
 Yes, now that my initial issue is solved, I'll head over to the measurements forum.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Ivan Beaver on March 23, 2018, 08:19:55 pm
Oh wow. You weren't kidding about putting it on the floor!  I'm amazed it gets nearly the response as outdoors!
 Yes, now that my initial issue is solved, I'll head over to the measurements forum.
The idea is to avoid reflections.

Even if the mic element is 1/4" off of the floor, you can see the reflections that are caused by that "large distance" (at least at the upper freq.)

A good idea is to point the mic directly towards the floor, with the end about the thickness of a business card from the floor.  YES, that close.

It depends on how high you want to measure.  As the "upper freq of interest" gets lower, the larger the distance the mic can be away from the boundary, and still get good results.

As I say all the time, you must ALWAYS ask yourself "What am I here to do?".

There are all kinds of things you CAN measure, but is it important for what you are trying to do at the moment.

I often do all sorts of measurements that "violate the basic rules", but when you start to realize the things that matter (and don't matter), you can ignore certain parts of the measurements, while you focus on what you are trying to see/measure
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on March 25, 2018, 08:18:38 pm
The idea is to avoid reflections.

Even if the mic element is 1/4" off of the floor, you can see the reflections that are caused by that "large distance" (at least at the upper freq.)
Ok, that totally makes sense.  Sound bouncing around the room is the problem - but in high frequencies, this becomes no issue (for direct measuring, anyway) because the waves are so much shorter.
Good info, it's appreciated.
Title: Re: How to measure
Post by: Mac Kerr on March 25, 2018, 08:30:32 pm
Ok, that totally makes sense.  Sound bouncing around the room is the problem - but in high frequencies, this becomes no issue (for direct measuring, anyway) because the waves are so much shorter.
Good info, it's appreciated.

No, just the opposite. At high frequencies it takes a small difference in path length between the direct sound and the reflected sound to create cancellations, with low frequencies (long wavelengths) it takes a much greater path length difference to have the same effect. You can eliminate many of the reflections off the floor by placing the mic element very close to the floor, making the path length differences very small. This also benefits longer wavelengths, but is critical for short wavelengths.

Mac
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Mark Wilkinson on March 26, 2018, 11:38:46 am
Maybe this will help illustrate what Ivan and Mac are saying about mic placement and short wavelengths.

Here are a couple of plots using the "1 meter, speaker and mic both on the floor technique" ......like previously pictured.
The first is a HF driver used from 6-7kHz up, the second is a mid driver used from 100-700Hz.   

On both, the green traces are with the mic pointing straight at the floor, almost touching the floor.
Reds are with the mic laying horizontal on the ground just as in the thread pict, which puts the capsule center about 3/8" off the floor.

Greens are more accurate because they have less floor bounce in them.
But note that the floor bounce only matters up high. 
Mid traces are nearly identical.
No smoothing on any to help see.

20 kHz has about 0.7" wavelength, so 3/8" off floor is a big proportion of that, with lots of interference.
And of course 3/8" means nothing to long wavelengths.....

Hope this helps..





 

Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Chris Grimshaw on March 28, 2018, 07:02:01 am
Hey Mark,

Just wondering if you've got a comparison of the same cabinets measured outdoors?
If this way of measuring is close, then that'd solve some issues for me.

Cheers,
Chris
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on March 28, 2018, 09:47:41 am
I made a couple measurements with the mic flat on the floor.  I will try them with the 'business card' approach next.
I was pleasantly surprised, however.  While the unprocessed signal needs eq-ing, I didn't see any huge nulls or peaks. I didn't save anything because I wanted to be more systematic than I had time.  I'll try to get to it again today.

I'd still like to check how the phase looks between my passive x-over and the active one. and between drivers.  I have yet to find an easy instructional here or elsewhere but haven't looked super hard.

I checked out the measurements forum here.  I found lots of interesting stuff but had a hard time quickly finding things specifically relevant to my project.
On many forums, not just this one, a general topic will often have thousands of posts, with many thousands of replies to them.  It's simply too much noise for someone new to that forum to sort before finding anything useful to the overall topic.
If I could make a suggestion.  Several 'sticky' posts covering things like general measurement techniques, different measurements and what they mean, adjusting, posting graphs etc. would be very helpful over there.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on March 28, 2018, 09:54:02 am
I made a couple measurements with the mic flat on the floor.  I will try them with the 'business card' approach next.
https://photos.app.goo.gl/50kzXONbeGBkexKw1
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Mark Wilkinson on March 28, 2018, 10:03:17 am
Hey Mark,

Just wondering if you've got a comparison of the same cabinets measured outdoors?
If this way of measuring is close, then that'd solve some issues for me.

Cheers,
Chris

Hi Chris, yes, see reply 29 in this thread....those traces are a 12" driver in a ported box, indoors vs outside (check my definition of 'outside')...

Maybe what might help you more, below is the double 12" mid box you worked on modeling for me...
The indoor measurement was made with it laying on its side like in prior pict.
Blue is indoors.

And then both sections of a bms coax, again blue traces are outdoors.

All the indoor traces are with the mic just laying horiz....I don't bother with pointing the mic into the floor anymore, because VHF is all that changes and i do final tuning for that outside.

This "measure with both speaker and mic on the floor" technique has been a hell of a blessing.  I read about it in a post from a guy on one of the more esoteric soundforum threads.  He a transducer designer I think, and highly recommended it. 
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Tim McCulloch on March 28, 2018, 10:46:56 am
If I could make a suggestion.  Several 'sticky' posts covering things like general measurement techniques, different measurements and what they mean, adjusting, posting graphs etc. would be very helpful over there.

We help out but we do not *train*.

Smaart and SysTune offer training (and SysTune training is done by at least 1 transducer/horn designer) to use their software and give general advice in practical measurement but individual transducer alignment for loudspeaker design is a highly specialized matter.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on March 28, 2018, 06:59:15 pm
Ok, so here is a measurement of the box with active crossover via the amp (red) and passive (green) This is with 1/12 smoothing.  Swept from 80Hz to 14k5  Both crossovers are LR 24 at 1k3.
The mic is about 2mm off the floor, pointing straight at the floor.  The box is about 2 feet away, angled down toward the mic.

https://photos.app.goo.gl/NW8WVbknJ55qmn1T2
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Art Welter on March 28, 2018, 10:14:37 pm
Ok, so here is a measurement of the box with active crossover via the amp (red) and passive (green) This is with 1/12 smoothing.  Swept from 80Hz to 14k5  Both crossovers are LR 24 at 1k3.
The mic is about 2mm off the floor, pointing straight at the floor.  The box is about 2 feet away, angled down toward the mic.

https://photos.app.goo.gl/NW8WVbknJ55qmn1T2
OK, now show the HF and LF output of each, so you can determine which is more like a "LR24" at 1k3 for the HF.
The 10dB spike at 7kHz in the passive crossover indicates an order of magnitude problem in the passive crossover, but will provide more "zing" to your strings...

Do bass players still boil their round wound strings?

Cheers,
Art
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on March 29, 2018, 02:50:11 pm
OK, now show the HF and LF output of each, so you can determine which is more like a "LR24" at 1k3 for the HF.
I will do so when I get home later.
The 10dB spike at 7kHz in the passive crossover indicates an order of magnitude problem in the passive crossover, but will provide more "zing" to your strings...
Zing is good, but I'd rather add manually :)  So, what - besides EQ - would I do to fix this if it's a crossover problem?  I can't really add another cap without phasing issues etc., can I?    Speaking of, I know a little about phasing, basically that you want the least turnover possible and not a lot of it close together.  What would I do to smooth it?  What's your favorite place to read about phasing?
Do bass players still boil their round wound strings?
You can get just a bit more life out of roundwounds if you do that, but by the time you get to the point of needing to boil them, they're dead.  You might get another couple hours out of 'em by boiling.  Still, dead isn't always bad.  It just means you aren't going to get the sound that roundwounds can give you.  They're still fine for a flatter, even tone. I prefer "dead" roundwounds to flatwounds for country R&B, etc.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Art Welter on March 29, 2018, 06:30:16 pm
1) So, what - besides EQ - would I do to fix this if it's a crossover problem? 
2)I can't really add another cap without phasing issues etc., can I?   
3)Speaking of, I know a little about phasing, basically that you want the least turnover possible and not a lot of it close together.  What would I do to smooth it?  4)What's your favorite place to read about phasing?
1) The fact that the 7 kHz peak is much smaller in the active crossover's response indicates the passive crossover has a problem. Incorrect values have inadvertently created a "tank circuit", a resonant peak in the response. There could be another lurking below the crossover frequency, masked by the woofer response.
2)The "phasing issues" are dependent on where the cap is placed in the circuit.
3) A smooth phase transition in the crossover region is easiest to achieve if the acoustical response of the two pass bands are symmetrical. The amount of crossover "poles" (capacitors or coils) needed to achieve a given slope can be quite different- a single cap or coil could make a 24 dB per octave slope.
Phase and frequency response smoothness are intertwined, generally component choices that result in smooth frequency response with the desired slope will also have smooth phase.
4) Merlijn van Veen has a lot of good "phase" stuff online, Bob "606" McArthy has good books, and the Audio Cyclopedia is great.
None of those sources get much into the nitty-gritty of real-world passive crossover design, which is kind of like making sausage..

I've built enough (electrical) second order crossovers to wager that getting a fourth order crossover right would be not twice, but at least four times more difficult.

Art
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Chris Grimshaw on March 30, 2018, 04:54:33 am
Hi Chris, yes, see reply 29 in this thread....those traces are a 12" driver in a ported box, indoors vs outside (check my definition of 'outside')...


Hey Mark,

Cheers for the data. Looks like a great way of doing things in the winter months.


Jeff,

That 7kHz peak says there's something really-not-quite-right with your crossover.
If you could provide ZMA and FRD files for your drivers, I'd be happy to put them through XSim and see how it looks.
I know REW can export ZMA and FRD files directly. Not tried with other software. You might be able to export as a .txt, though, which I'd probably be able to work with.

Chris
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on March 30, 2018, 02:36:52 pm
I've built enough (electrical) second order crossovers to wager that getting a fourth order crossover right would be not twice, but at least four times more difficult.
That is great info, thank you!  I have some reading to do.
It kinda looks like I got lucky in the passband region.  The only error is with the 7K peak.  I'm thinking that using a calculator as I did could have turned out much worse.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on March 30, 2018, 02:47:39 pm
That 7kHz peak says there's something really-not-quite-right with your crossover.
If you could provide ZMA and FRD files for your drivers, I'd be happy to put them through XSim and see how it looks.
I know REW can export ZMA and FRD files directly. Not tried with other software. You might be able to export as a .txt, though, which I'd probably be able to work with.
That is very kind of you!  First I will measure each driver and put up a curve for each separately as requested earlier.  I'll do some reading and see how to extract those files for you, It'd be great to have that kind of help, thanks!
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on March 30, 2018, 09:31:20 pm
Here are graphs of each side of the X-over separately.  All have 1/12 smoothing applied.

This is with the active crossover engaged.
https://photos.app.goo.gl/WRbCrIePue3m3qoX2

This is with the passive crossover.
https://photos.app.goo.gl/BobnJELYpVaffZX22

This is all four sweeps together. 
https://photos.app.goo.gl/GOy7BeBs2sZvoRi63

I'm working on full range samples, and how to export them as .zma files...
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on March 30, 2018, 10:06:58 pm
Apparently, it's quite a chore to make impedance measurements and thus .zma files in REW.  If I gave you the model names of the drivers can it be done?
Supposedly the frequency measurements can be done as exports, though.
See if these work
https://drive.google.com/open?id=1J0Z8C9Xg8qXQsul62WjRpA4rNbj8YG6G
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Chris Grimshaw on March 31, 2018, 05:15:07 am
Apparently, it's quite a chore to make impedance measurements and thus .zma files in REW.  If I gave you the model names of the drivers can it be done?

The FRD files work fine.

For the ZMA, you really do need the measured impedance - a HF driver + horn combination will have a specific impedance curve that the datasheets won't tell you. Same for LF driver + cabinet.

Easy enough to make an impedance jig, though. I got a pair of cheap guitar cables, cut them in half, and soldered the correct connections with a 100ohm resistor in the middle. Chop one "head" off and put a SpeakOn on there, job done. 10 minute job to throw that together if, like me, you happen to have boxes full of misc. cables.


I'm not sure if you've posted it, but if you've got a crossover schematic labelled with all the component values you've used (preferably measured values), that'd be great - I can start by simulating what you've got and then suggest tweaks and show before/after curves.


Chris
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on March 31, 2018, 11:01:24 am
The FRD files work fine.
Glad to hear, that part is easy.
For the ZMA, you really do need the measured impedance - a HF driver + horn combination will have a specific impedance curve that the datasheets won't tell you.
This is because of how the driver couples with the horn?  The acoustic load changes the impedance? I know this is true with cones, I just didn't expect it with a CD.
Easy enough to make an impedance jig, though. I got a pair of cheap guitar cables, cut them in half, and soldered the correct connections with a 100ohm resistor in the middle.
* EDIT * Found a graphic, easy enough, I'll make one.
Chop one "head" off and put a SpeakOn on there, job done.
That might be a problem, see the drawing I'll post.  It needs at least three poles to make the right connections.
10 minute job to throw that together if, like me, you happen to have boxes full of misc. cables.
I have millions just waiting for something like this. :)
So then, do I make this measurement with/through the crossover? On each driver separately or together with X-over? I'm assuming this should be done with the drivers in the box?  Sorry for the hand-holding.  I've noticed that many folks who post instructions about topics like this make it unnecessarily complicated to understand.  I'll keep reading though, your words give me a better picture of what needs to be done, so maybe I can decipher their instructions better.
I'm not sure if you've posted it, but if you've got a crossover schematic labelled with all the component values you've used (preferably measured values), that'd be great - I can start by simulating what you've got and then suggest tweaks and show before/after curves.
Yes, and the values of the caps are very close to stated values. I measured all of them.  The inductors are exact to .1mH.

Switch:
https://photos.app.goo.gl/LqaIuZ0fJNVfAsaq2

Crossover:
https://photos.app.goo.gl/px4Gk9Q5RI9H5CMn1

Note - I omitted the L-Pad in the real thing.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Chris Grimshaw on March 31, 2018, 12:06:16 pm
Hey Jeff,

I'd like the impedance of the drivers in the boxes, please. No crossover stuff. Yes, the horn changes the impedance curve. Just like putting a cone driver on a horn, a HF unit will show impedance changes, too.

We all start somewhere. I'm happy to post up screenshots of XSim so you can follow along.

I know what you mean about having a million little projects. I've got some nice Fostex full-range units that need boxes, plus I'm doing some low-profile PA subs, and there's the pile of 2.5" full-range units that'll become a column speaker eventually, and the big pile of amplifiers that need repair work...
It never ends.


In the mean time, try this.

Here are some measurements which you can import into XSim. The HF unit will go down to 1kHz with a minimum 12dB/octave slope. See what you come up with. Assume the amplifier is capable of driving 4ohm just fine, but impedance drops below that should be avoided - in an emergency, you should be able to run two of these on a single 2ohm-capable amplifier.
The midbass driver is 6.5", so crossing over below 3kHz would be good - it starts beaming up there.

https://drive.google.com/open?id=12hWL4d06UqV-RSzMKDr9lpjK0GR-FDPo

My crossover for those looks like this, but try on your own first:
(https://static.wixstatic.com/media/59f09e_6584f9011fcc4b4e99ece22569220ca7~mv2.jpg/v1/fill/w_852,h_569,al_c,q_90/59f09e_6584f9011fcc4b4e99ece22569220ca7~mv2.jpg)

Though I went to 8ohm instead of 7 for the final build as space was tight and the 7ohm resistor was made up of a 4R7 and a 2R2. Didn't change the HF level much.

Once you've got to grips with XSim, it's very easy to make the relevant measurements with REW or similar and import them to design a crossover. When it comes to doing that, my recommendation would be to have some 0.5uF and 1uF caps on-hand, plus a couple of 0.1mH inductors, so you can increment values without having to order yet more components.

Chris
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: David Morison on March 31, 2018, 12:24:24 pm
Here are graphs of each side of the X-over separately.  All have 1/12 smoothing applied.


This is with the passive crossover.
https://photos.app.goo.gl/BobnJELYpVaffZX22


I know they're 30-odd dB down from nominal but it looks like there are at least 2 low freq peaks in the response of the HF driver visible at 30 & 60Hz - those should definitely not be there. Something might still be up with your wiring. Might be worth readjusting the vertical scale of the window to see more of what's going on down there?

Edit - Or: at least check the coherence to see if they might be from some kind of background noise.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on April 01, 2018, 09:58:56 pm
I'd like the impedance of the drivers in the boxes, please. No crossover stuff.
Took me all afternoon to figure out the routing and ASIO drivers with my digital mixer and a little more to make the jig, but I * think * I got the measurements you need.  Check these out.

https://drive.google.com/file/d/1QR9XHpxILlpV1I5DLdJGbVK0ucqLnrAw/view?usp=sharing

In the mean time, try this.
I can just use my own drivers now I suppose, right?  Still, I'm curious to see what you'll come up with now that we know the real values.

Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on April 01, 2018, 10:00:24 pm
I know they're 30-odd dB down from nominal but it looks like there are at least 2 low freq peaks in the response of the HF driver visible at 30 & 60Hz
I live in a small apartment, it's not exactly quiet.  Those could have been my cat walking by.  :)
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Chris Grimshaw on April 03, 2018, 06:14:42 am
Hi Jeff,

I downloaded the ZMAs, they work fine.

I had a look at your crossover schematic and found it difficult to follow without tracing it all out, so I ditched it and started from scratch.

Here's attempt 1:

4th order highpass, 2nd order lowpass. The 2ohm resistor on the HF side drops the HF level by a dB or so. I set off with a passive crossover calculator to get some rough values, and then deleted half of it and re-tuned the rest. Results weren't good to start with.
After a while, I got this.

(https://static.wixstatic.com/media/59f09e_3d335cb7c55c414eaef22a6ee2cbb20b~mv2.jpg/v1/fill/w_1266,h_719,al_c,q_90,usm_0.66_1.00_0.01/59f09e_3d335cb7c55c414eaef22a6ee2cbb20b~mv2.jpg)

I wasn't too happy with the overlap region. While the two bands do seem to sum together quite well, the overlap is coming up to around an octave, which will give some weird polars.

So, attempt two.
Third order highpass, second order lowpass. 3rd order is much easier to get right than 4th order, and still offers a useful amount of tweeter protection. A second order highpass should be avoided, IMO, as a 12dB/octave slope produces constant excursion as frequency decreases. Of course, when you add in the acoustic slope of the tweeter things will get better. Still, it's quite a lot of out-of-band energy.

I did try higher orders on the LF section, but invariably found that cutting out the extra components made life easier.

(https://static.wixstatic.com/media/59f09e_266cb53f6e7b495db8dc9b038f67d1cb~mv2.jpg/v1/fill/w_1268,h_719,al_c,q_90,usm_0.66_1.00_0.01/59f09e_266cb53f6e7b495db8dc9b038f67d1cb~mv2.jpg)

A couple of notes on this one:

R1 drops the Q of the crossover a little. Without it, there's a bit of a peak from the interaction between the inductor and capacitors. Limiting the low-frequency short-circuit that the inductor presents smooths this out quite well.
R2 is an optional 2ohm resistor that alters the HF level. I'd bypass it with a reasonably heavy-duty switch and call it a "bright" switch. The level difference is around 2dB across the kHz band. If you've got a fairly "dead" room, then shorting that resistor will bring the HF level up a bit, and conversely, if the room is quite "lively", then dropping the HF level a touch will be useful.
Both frequency response curves (with/without R2) would be perfectly acceptable IMO, and should be chosen according to the use case.

Both R1 and R2 see up to 50% of the power going into the HF driver, and should be sized accordingly.

Chris
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on April 03, 2018, 11:04:07 am
I downloaded the ZMAs, they work fine.
Excellent!  It was a good exercise learning how to make it happen.
I had a look at your crossover schematic and found it difficult to follow without tracing it all out, so I ditched it and started from scratch.
I can get you an actual schematic if you like.  That was a layout map factoring the physical sizes of the components and hookup leads to the switch and input.  The x-over is exact to the online calcs, they're both LR-4 with passband @ 1K3.
So, attempt two.
Third order highpass, second order lowpass. 3rd order is much easier to get right than 4th order, and still offers a useful amount of tweeter protection. A second order highpass should be avoided, IMO, as a 12dB/octave slope produces constant excursion as frequency decreases. Of course, when you add in the acoustic slope of the tweeter things will get better. Still, it's quite a lot of out-of-band energy.
I did try higher orders on the LF section, but invariably found that cutting out the extra components made life easier.
A couple of notes on this one:
R1 drops the Q of the crossover a little. Without it, there's a bit of a peak from the interaction between the inductor and capacitors. Limiting the low-frequency short-circuit that the inductor presents smooths this out quite well.
What is the value of R1?  I can't quite make it out.  Are there any phasing issues with using a 3rd order and a 2nd order?  Is that accounted for with X-Sim?
  See how on the first measurement pix I sent that BOTH active and passive x-overs result in that 7K peak?  Why would the active do that also, if it was an issue with the passive X-over?
See the nulls at about 250 and 500?  I was kinda guessing that was room response or the box, but it looks as though those happen on your impedance graphs too? Will that need to be eq'ed?
R2 is an optional 2ohm resistor that alters the HF level.
I think that since this is a bass rig, the tone controls on the bass or preamp will have vastly more influence on the signal.  Still, it's interesting to note.
Both R1 and R2 see up to 50% of the power going into the HF driver, and should be sized accordingly.
Is there a way to see a ratio or percentage of the power division?  I know the highs see a small fraction of the lows, but those resistors still may need to be quite substantial in power handling.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on April 03, 2018, 12:35:48 pm
Here is the design I have in the box right now.

https://photos.app.goo.gl/Qt5koyKLkFLWvkfQ2
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Chris Grimshaw on April 03, 2018, 05:25:05 pm
Excellent!  It was a good exercise learning how to make it happen.I can get you an actual schematic if you like.  That was a layout map factoring the physical sizes of the components and hookup leads to the switch and input.  The x-over is exact to the online calcs, they're both LR-4 with passband @ 1K3.What is the value of R1?  I can't quite make it out.  Are there any phasing issues with using a 3rd order and a 2nd order?  Is that accounted for with X-Sim?
  See how on the first measurement pix I sent that BOTH active and passive x-overs result in that 7K peak?  Why would the active do that also, if it was an issue with the passive X-over?
See the nulls at about 250 and 500?  I was kinda guessing that was room response or the box, but it looks as though those happen on your impedance graphs too? Will that need to be eq'ed?I think that since this is a bass rig, the tone controls on the bass or preamp will have vastly more influence on the signal.  Still, it's interesting to note.Is there a way to see a ratio or percentage of the power division?  I know the highs see a small fraction of the lows, but those resistors still may need to be quite substantial in power handling.

Hi Jeff,

I'm not sure this is in any particular order, but...

R1 is 1.8ohm.

XSim accounts for driver & crossover phase. A textbook crossover only works properly when both drivers have a flat frequency response and impedance curve around the crossover frequency, preferably for half an octave each way, minimum. When we're dealing with real drivers with impedance wiggles and a non-linear frequency response, a little more creativity is required.

I didn't realise this was for a bass rig. In that case, yes, the tone controls will have much more effect. I'd skip the resistor leading into the HF section.

If you go under "Add Graph", and then "More", you can get a graph of power dissipation by component, and then choose whichever component you like. Double-click on the amplifier to ramp up the voltage. Each resistor dissipates roughly half of what the compression driver would be dissipating, so I'd recommend something reasonably heavy-duty. Maybe aluminium clad and bolted to the SpeakOn plate - handy little heatsink there. That rather depends on how much power you're planning on putting into this cab - if it's just bass guitar, you might well get away with a fairly low-power resistor as bass guitar rarely has much content above a couple of kHz compared to lower down. If it might see use as a full-range cabinet for vocals or monitoring, then I'd make sure the resistor will take at least as much power as the compression driver.

The impedance wiggles associated with the 500Hz peak/dip says to me you've got a cabinet resonance. Maybe a standing wave. It could also be midrange leaking out of the bass port.

The narrow 7kHz peak doesn't show up on the FRD files, so it looked to me like it was a measurement artifact that's since been rectified. Any ideas?

Chris
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on April 03, 2018, 07:42:31 pm
XSim accounts for driver & crossover phase. A textbook crossover only works properly when both drivers have a flat frequency response and impedance curve around the crossover frequency, preferably for half an octave each way, minimum. When we're dealing with real drivers with impedance wiggles and a non-linear frequency response, a little more creativity is required.
So it account for phase issues as well.  I understand phase pretty well, and how it relates to frequency curves.  I get that they work hand in hand.  I'm wondering if an improved crossover will actually sound better.  I know the freq. curve is only half of the story, but it seems to me in looking at these graphs that the improvements with optimal over what I have installed won't be immediately audible - at least not unless you could A/B two identical boxes side by side.  Am I wrong?
I didn't realise this was for a bass rig. In that case, yes, the tone controls will have much more effect. I'd skip the resistor leading into the HF section.
Agreed.  There is very little above 5K I'm interested in any way. A little EQ will work if I ever used it for something other than bass.
If you go under "Add Graph", and then "More", you can get a graph of power dissipation by component, and then choose whichever component you like. Double-click on the amplifier to ramp up the voltage. Each resistor dissipates roughly half of what the compression driver would be dissipating, so I'd recommend something reasonably heavy-duty. Maybe aluminium clad and bolted to the SpeakOn plate - handy little heatsink there. That rather depends on how much power you're planning on putting into this cab - if it's just bass guitar, you might well get away with a fairly low-power resistor as bass guitar rarely has much content above a couple of kHz compared to lower down. If it might see use as a full-range cabinet for vocals or monitoring, then I'd make sure the resistor will take at least as much power as the compression driver.
Cool, I'll play around with that.  Nice to know it has that ability.
The impedance wiggles associated with the 500Hz peak/dip says to me you've got a cabinet resonance. Maybe a standing wave. It could also be midrange leaking out of the bass port.
500-ish is very likely with a box this small.  That wouldn't show up on WinISD either...  It could even be bouncing back through the cones.  I took all the stuffing out before I did this new X-Over.  I had put it in there by ear, maybe I ought to measure with it.
The narrow 7kHz peak doesn't show up on the FRD files, so it looked to me like it was a measurement artifact that's since been rectified. Any ideas?
Yep, it may have been a resonance off the floor tile or something.  I will move the box somewhere else, maybe put it on the carpet or something further away or closer to the mic and measure.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Chris Grimshaw on April 04, 2018, 04:00:16 am
So it account for phase issues as well.  I understand phase pretty well, and how it relates to frequency curves.  I get that they work hand in hand.  I'm wondering if an improved crossover will actually sound better.  I know the freq. curve is only half of the story, but it seems to me in looking at these graphs that the improvements with optimal over what I have installed won't be immediately audible - at least not unless you could A/B two identical boxes side by side.  Am I wrong?

Agreed.  There is very little above 5K I'm interested in any way. A little EQ will work if I ever used it for something other than bass.

Cool, I'll play around with that.  Nice to know it has that ability.

500-ish is very likely with a box this small.  That wouldn't show up on WinISD either...  It could even be bouncing back through the cones.  I took all the stuffing out before I did this new X-Over.  I had put it in there by ear, maybe I ought to measure with it.Yep, it may have been a resonance off the floor tile or something.  I will move the box somewhere else, maybe put it on the carpet or something further away or closer to the mic and measure.

Hi Jeff,

I recently had a similar problem - choppy midrange from a ported box. You can see some graphs here: http://www.diyaudio.com/forums/pa-systems/271132-chris661s-pa-system-thread-9.html#post5355295

In the end, it was quite a lot of wool underlay to get the results I was after, but the cabinets sound exceptionally clean now. I think there was around 30mm of material directly between the port and the driver to get the "final" result.


With regards to the audibility of changes to the crossover, I suspect the difference will probably be audible with music playback. With bass guitar, maybe, maybe not. Bass/guitar cabinets are usually chosen for their "sound", rather than having a flat frequency response, so if you're happy with how the cabinet sounds as-is, I'd be inclined to keep it. The second-order lowpass takes out an inductor (with its associated DCR) from the woofer side, so you'll get a smidge more power delivery, but that's about it.

Interested to see if the new measurements work out better.

Chris
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on April 04, 2018, 11:02:16 am
I recently had a similar problem - choppy midrange from a ported box. You can see some graphs here: http://www.diyaudio.com/forums/pa-systems/271132-chris661s-pa-system-thread-9.html#post5355295
In the end, it was quite a lot of wool underlay to get the results I was after, but the cabinets sound exceptionally clean now. I think there was around 30mm of material directly between the port and the driver to get the "final" result.
Hi Chris,
I actually read that very thread about 6 months ago when I was trying to understand why it's no longer valid to stuff LF/sub boxes. I ended up with a 2x18 box with 18-sound drivers which is very nearly flat outdoors to 30 Hz with no stuffing.  I think you're exactly right about issues caused by unwanted sound reflecting back through the ports and cones.  I had stuffed this box by ear before. Subjectively it sounded better.  Time to play around with stuffing and measuring. 
With regards to the audibility of changes to the crossover, I suspect the difference will probably be audible with music playback.
Now I wish I had two of these boxes.  I suspect that while there are small differences visible on the graphs, it'd be pretty tough to hear.  I think going after those big scoops in the midrange will be more audible.  Since I can, do you think I ought to phase align between the high and the mid when using the active x-over in my amp? each driver is on its own channel, meaning I could add delay to either.
Bass/guitar cabinets are usually chosen for their "sound", rather than having a flat frequency response
My rig has always been about combatting that nasty distorted fart-bass made by store-bought rigs once they rise above 85dB outside the store. I want the reproduction to be as accurate as possible, like an ideal PA.  I'll make the 'sounds' with my instrument, preamp, and compressor.
Interested to see if the new measurements work out better.
  Me too.  I'll try to do some more today.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: David Morison on April 04, 2018, 03:52:23 pm
Hope you don't mind a few thoughts from the peanut gallery...

Regarding the spike at 7kHz, I notice that it is much less pronounced in the FRD file than in the REW screengrab posted earlier. Was the FRD file extracted from that exact measurement, or did you re-measure the cab to generate that perhaps? If the latter, did you notice if the 7kHz spike was still there 2nd time round?
If you measured the cab in a different location, it is perhaps possible that some at least of the spike was some kind of reflection. Likewise, if any of the midrange troughs were reflection/room based, then simply moving the cab could fix them (or indeed maybe just move them to different frequencies!).

I had a play with XSim too, and have come up with a slightly different take.

(https://i.imgur.com/9bZ47V3.jpg)

Definitely not saying it's better than Chris's, but perhaps it'll show some of what is possible (and the tradeoffs involved too).
Working on the assumption that the 7kHz spike is real and needs a bit of help, I've tried to flatten that range a bit more.
This does make the circuit more complicated, and results in a greater impedance swing, so it would be marginally harder to drive if your amp didn't like inductive loads. (Modern solid state amps should be fine, but if you got a retro valve amp at some point, it might become an issue.) It also has slightly higher insertion loss than Chris's.

I've done a lineup of the original circuit, Chris's and mine on the same graph so you can hopefully see the differences a bit easier too.

(https://i.imgur.com/QgniJqp.jpg)

Cheers,
David.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on April 04, 2018, 07:25:30 pm
Hope you don't mind a few thoughts from the peanut gallery...
Not at all, that's why I posted...
Regarding the spike at 7kHz, I notice that it is much less pronounced in the FRD file than in the REW screengrab posted earlier. Was the FRD file extracted from that exact measurement, or did you re-measure the cab to generate that perhaps? If the latter, did you notice if the 7kHz spike was still there 2nd time round?
I did not notice it.  Yes, it's a different measurement.  Excellent - chalk that up to room anomaly.
If you measured the cab in a different location, it is perhaps possible that some at least of the spike was some kind of reflection. Likewise, if any of the midrange troughs were reflection/room based, then simply moving the cab could fix them (or indeed maybe just move them to different frequencies!).
I am going to measure in a different location in a few minutes.  Also, I'll play with stuffing a blanket in there and see what happens, I will post results.
I had a play with XSim too, and have come up with a slightly different take.
Definitely not saying it's better than Chris's, but perhaps it'll show some of what is possible (and the tradeoffs involved too).
Working on the assumption that the 7kHz spike is real and needs a bit of help, I've tried to flatten that range a bit more.
This does make the circuit more complicated, and results in a greater impedance swing, so it would be marginally harder to drive if your amp didn't like inductive loads. (Modern solid state amps should be fine, but if you got a retro valve amp at some point, it might become an issue.) It also has slightly higher insertion loss than Chris's.
I have tons of solid state power available, so that isn't an issue.  I'm still wondering how much the real audible difference would be.  I know that when I flip from this passive design to the active crossover and bi-amp, there is a difference - it's a bit clearer and defined, but the difference is small and only noticeable with music, and then only if you flip back and forth.  If we're designing for theory and optimal, sure it's good to improve, but for practical use?  I may be to my goal already.
Which brings me to a second realization.  In the first measurement I posted, that 7K spike was there with the active X-Over too, meaning it's a really good bet it's a room anomaly, and not my design.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Art Welter on April 04, 2018, 08:35:58 pm
If we're designing for theory and optimal, sure it's good to improve, but for practical use?  I may be to my goal already.
Which brings me to a second realization.  In the first measurement I posted, that 7K spike was there with the active X-Over too, meaning it's a really good bet it's a room anomaly, and not my design.
Jeff,

Your passive crossover is actually reducing the midrange from 2kHz to 5kHz by about 5 dB in both your initial woofer/HF test and the later tests of the HF only. That difference is not a "room anomaly".

The low end of the passive crossover is "safe", which could not be determined by the initial woofer/HF test. The passive crossover's midrange attenuation could be considered a "loudness contour" feature.

"Good enough", EQ to taste..;^).
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on April 04, 2018, 10:07:09 pm
So here it is WITH a blanket stuffed in the box:

https://photos.app.goo.gl/W4he4YkTJRiIkvWu2

Here it is without:

https://photos.app.goo.gl/ae6nv2z5FRGNDyJC3

These two are with EQ from about 2.5 K and up.  Without that EQ though, unfortunately, there is still the "nasty 7K" even though I moved the speaker a few feet and facing a different direction.  The good news is that if I get some actual stuffing (instead of my favorite blankie) and play around with it, the lower half can be improved significantly.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on April 04, 2018, 10:12:12 pm
Your passive crossover is actually reducing the midrange from 2kHz to 5kHz by about 5 dB in both your initial woofer/HF test and the later tests of the HF only. That difference is not a "room anomaly".
The low end of the passive crossover is "safe", which could not be determined by the initial woofer/HF test. The passive crossover's midrange attenuation could be considered a "loudness contour" feature.
This is just now, the attenuation between active and passive is about 5 dB across the spectrum.
https://photos.app.goo.gl/jXrQAcXpCRvnNleK2
"Good enough", EQ to taste..;^).
LOL, Okay, point taken :)
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Chris Grimshaw on April 05, 2018, 03:46:14 am

I had a play with XSim too, and have come up with a slightly different take.


Cheers,
David.

Nice way of getting a notch filter in there, I like that.
Jeff, that design requires more components, but definitely gives a better response. Thumbs-up from me.

Chris

PS - IIRC, XSim applies 1/12th octave smoothing to the input measurements as they can often be very "fuzzy".
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: David Morison on April 05, 2018, 05:39:41 am
Nice way of getting a notch filter in there, I like that.
Jeff, that design requires more components, but definitely gives a better response. Thumbs-up from me.

Chris

PS - IIRC, XSim applies 1/12th octave smoothing to the input measurements as they can often be very "fuzzy".

Yeah, I started with modelling the original with Jeff's components & tweaking their values, then added a full notch filter after the main XO. While playing with the values I realized that the capacitor of the notch filter was getting close to the value of the second cap in the HPF, so I shifted the inductor & resistor over to see what happens. Obviously, co-opting that cap to become part of the notch reduces its effect on the main crossover function, so although it looks like a 4th order layout the net slope is closer to 3rd order.
That's also why the second inductor needs to stay in - otherwise the net slope would be shallower and there would be less control of the shape of the knee of the HPF. Given the big peak around 1.2kHz, having control of the shape of the knee was essential.

The depth of the notch can be adjusted by varying the resistor value - increasing it deepens the notch, but also reduces the impedance at that frequency range and increases the phase shift of the impedance so one can't go too far without it becoming a more challenging load for the amp.

I did notice there were options for smoothing in displaying the traces in XSim, I think I've stuck to 1/24 though.
Perhaps if the program's already applying some before my selection (on top of any smoothing in the original measurement before converting to the FRD format) that may explain why Xsim is showing much less of the 7kHz spike.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Steve M Smith on April 05, 2018, 08:21:16 am
You can see what happened here: http://www.diyaudio.com/forums/pa-systems/271132-chris661s-pa-system-thread-9.html#post5359495

Did you ever make the small sub illustrated on post No. 84? (I haven't read the whole of the thread yet).

Like you, I mainly do folk/acoustic events when using my own equipment.  I often think about building my own speakers (I have done in the past) and swap between wanting something similar to what you showed on that post. i.e. a small sub and small top, perhaps 6" or 8" with horn or just making larger three way range cabinets with enough bass response.

If I had the money, the little KV2 6" speakers I saw at PLASA last year would be perfect!


Steve.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on April 05, 2018, 10:34:04 am
Jeff, that design requires more components, but definitely gives a better response. Thumbs-up from me.
I'm going to do it.  I have the caps, I can use the two large inductors to make the three smaller ones (I wrap them myself) and I do have some low-value 5W resistors I can probably cobble together to get 7.5ohms or thereabouts with necessary power handling.

Seeing that the LF side doesn't change much, I can leave that alone instead of re-making it as well for labor and cost reasons?

Also - The 7K spike happens with my x-over, AND with the active one in the amp.  Shouldn't an 'ideal' crossover show some improvement there?  I'm wondering if there's something else we've overlooked which is causing that 7K spike which shouldn't be there...
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Art Welter on April 05, 2018, 02:05:48 pm

Also - The 7K spike happens with my x-over, AND with the active one in the amp.  Shouldn't an 'ideal' crossover show some improvement there?  I'm wondering if there's something else we've overlooked which is causing that 7K spike which shouldn't be there...
Jeff,
A passive crossover can be designed with a notch filter to reduce a peak.

Your passive shows a midrange "depression" from around 2kHz to 5kHz, which makes the upper peak seem relatively larger.

This could either be either midrange attenuation, or a dual "tank circuit" boosting the low and top response, if you compare the raw driver response to the passive crossover you can determine which it is.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on April 05, 2018, 02:34:05 pm
Jeff,
A passive crossover can be designed with a notch filter to reduce a peak.

Your passive shows a midrange "depression" from around 2kHz to 5kHz, which makes the upper peak seem relatively larger.

This could either be either midrange attenuation, or a dual "tank circuit" boosting the low and top response, if you compare the raw driver response to the passive crossover you can determine which it is.
Hi Art,
Here are measurements for the raw drivers, in the box with no processing or x-over. 
https://photos.app.goo.gl/eTlH4dGOVRvF4utG3
I find it really odd that both my active x-over in my amp, AND the passive x-over design introduce the 7K spike.  If it were just my passive, then we'd have a winner, but the same happens with the digital one in my amp?  I feel like I'm missing something that has nothing to do with the x-overs..
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: David Morison on April 05, 2018, 02:46:13 pm
I'm going to do it.  I have the caps, I can use the two large inductors to make the three smaller ones (I wrap them myself) and I do have some low-value 5W resistors I can probably cobble together to get 7.5ohms or thereabouts with necessary power handling.

Seeing that the LF side doesn't change much, I can leave that alone instead of re-making it as well for labor and cost reasons?

Also - The 7K spike happens with my x-over, AND with the active one in the amp.  Shouldn't an 'ideal' crossover show some improvement there?  I'm wondering if there's something else we've overlooked which is causing that 7K spike which shouldn't be there...

If re-using components matters a lot, here's the best way of using the values you already have. It's not quite as flat as my first one, but still isn't bad.
Re-using the 8.2uF cap forces the actual notch to be a tiny bit lower than 7kHz so increasing the Resistor value to deepen the notch won't be quite as effective with this version. It also raises a second, smaller peak around 4.5kHz.

Regarding your latest measurements, that does look close to the response in the FRD file, with a minor peak at 6kHz rather than the full blown spike at 7kHz, so if anything that validates the designs Chris & I have suggested.

Edit PS - don't try to use the whole LF section of your current build, unless you want a hump from ~500Hz to 1kHz then a scoop at 1-2kHz.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on April 05, 2018, 03:34:03 pm
If re-using components matters a lot, here's the best way of using the values you already have. It's not quite as flat as my first one, but still isn't bad.
Super cool!
Regarding your latest measurements, that does look close to the response in the FRD file, with a minor peak at 6kHz rather than the full blown spike at 7kHz, so if anything that validates the designs Chris & I have suggested.
I'm not following - those are using EQ to flatten. (?)

Edit PS - don't try to use the whole LF section of your current build, unless you want a hump from ~500Hz to 1kHz then a scoop at 1-2kHz.
Again though, I know it shows that on the simulation, but the actual measurements don't.  The real world is what counts, right? https://photos.app.goo.gl/6wsU81O7ApafyA7s1
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Chris Grimshaw on April 06, 2018, 03:30:16 am
Did you ever make the small sub illustrated on post No. 84? (I haven't read the whole of the thread yet).

Like you, I mainly do folk/acoustic events when using my own equipment.  I often think about building my own speakers (I have done in the past) and swap between wanting something similar to what you showed on that post. i.e. a small sub and small top, perhaps 6" or 8" with horn or just making larger three way range cabinets with enough bass response.

If I had the money, the little KV2 6" speakers I saw at PLASA last year would be perfect!


Steve.

Hey Steve,

Haven't made the subs yet, though I'm hoping to get them done by the end of the month. There was a bit of messing around with the drivers - T/S parameters were measured and double-checked, and the drivers don't have as much Xmax as I thought so it'll probably be tuned around 60Hz to keep output levels sensible. 40Hz would be lovely, but isn't really viable. They'll also be slot-loaded, which means the port and driver output will be on the same face of the cabinet - better for positioning.

The KV2 speakers are pretty good. I heard them at PLASA Leeds (going again this year). Unfortunately, the guy demoing things wasn't allowed to run them without the sub(s), so it's difficult to tell how much work the tops are really doing. The ones I've built sound pretty solid on their own, but will go much much louder if you highpass them and give them a sub to play with.

Let me know if you'd like to kick some design ideas around - always happy to chat.

Chris

PS - Jeff, sorry for the off-topic post.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: David Morison on April 06, 2018, 04:29:09 am
Quote from: David Morison
Regarding your latest measurements, that does look close to the response in the FRD file, with a minor peak at 6kHz rather than the full blown spike at 7kHz, so if anything that validates the designs Chris & I have suggested.
I'm not following - those are using EQ to flatten. (?)

OK, I didn't explain myself terribly well.
I've been operating with the underlying uncertainty that if the FRD file doesn't have the 7kHz spike, then it may be based on measurements that are not valid.
If that is the case, then any design work done on the basis of that file may also not be valid.

In Reply no 75 just one post above mine, you post measurements which you state have no processing, yet they still show no 7kHz spike.

Therefore, you have managed to get a measurement that excludes the spike.

That implies the FRD file is in fact valid, so Chris & I haven't wasted time working with unreliable/incomplete data. This is a good thing  :)

So, you need to figure out what was different about that measurement run compared to the others.

Troubleshooting 101 can be summed up by a couple of simple rules.
1: Change only one thing at a time. For example, it's no good changing both the amp and the measurement mic for the same test, because if you got a different result, you wouldn't know which one caused the difference.
2: Divide and conquer. If in doubt, split the signal chain in half and measure there- if the artifact show up in one half of the chain and not the other, you've narrowed down where else to carry on looking.

Good luck,
David.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on April 06, 2018, 11:24:20 am
PS - Jeff, sorry for the off-topic post.
No worries!  I like the stained cabinets.  Sets you apart, and touch-up is simple.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on April 06, 2018, 11:44:50 am
I've been operating with the underlying uncertainty that if the FRD file doesn't have the 7kHz spike, then it may be based on measurements that are not valid.
If that is the case, then any design work done on the basis of that file may also not be valid.
David -
Now I know where I'm miscommunicating to you guys. Apologies for not being clear myself. 
Okay, so we know that when the drivers are measured alone, with no processing, etc. we get the response (and the .FRD files) I linked to in post 75. - i.e. no 7K spike.
We know a 7K spike is introduced when my passive X-over is placed in the series.  This is what we're troubleshooting.
 
BUT - and here's what I'm getting at.  When we switch from my PASSIVE crossover in the box, to the ACTIVE one in my amp (same cable, same amp, box, connectors, drivers) we get the SAME 7K spike.  IOW, why is that spike still there with a supposedly optimal active, digital crossover?
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: David Morison on April 06, 2018, 02:19:28 pm
David -
Now I know where I'm miscommunicating to you guys. Apologies for not being clear myself. 
Okay, so we know that when the drivers are measured alone, with no processing, etc. we get the response (and the .FRD files) I linked to in post 75. - i.e. no 7K spike.
We know a 7K spike is introduced when my passive X-over is placed in the series.  This is what we're troubleshooting.
 
BUT - and here's what I'm getting at.  When we switch from my PASSIVE crossover in the box, to the ACTIVE one in my amp (same cable, same amp, box, connectors, drivers) we get the SAME 7K spike.  IOW, why is that spike still there with a supposedly optimal active, digital crossover?

Well, the answer is whatever was different about the measurement run that generated the spike-less data.
It might not be obvious, but there must have been something else different.
When you got the flatter measurements, was the switch perhaps out of circuit, but in circuit for every other measurement?
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Chris Hindle on April 06, 2018, 02:40:26 pm

 
BUT - and here's what I'm getting at.  When we switch from my PASSIVE crossover in the box, to the ACTIVE one in my amp (same cable, same amp, box, connectors, drivers) we get the SAME 7K spike.  IOW, why is that spike still there with a supposedly optimal active, digital crossover?

The passive X-over is COMPLETELY disconnected from ALL the drivers, right?
Chris.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on April 06, 2018, 02:51:32 pm
The passive X-over is COMPLETELY disconnected from ALL the drivers, right?
During "active" mode (the amp's crossover is being used with both channels) The negative of the woofer remains connected to the negative of the passive x-over. But there is nothing in series on that pathway, from the woofer to the negative terminal on that channel. The high side is switched to its own channel and not connected to the passive crossover at all.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on April 06, 2018, 07:27:34 pm
Well, the answer is whatever was different about the measurement run that generated the spike-less data.
It might not be obvious, but there must have been something else different.
It 'could' be possible that I didn't defeat the EQ when running the full-range tests, but I really doubt it. Plus, I would have had to do that twice. Still, 'doubt' and 'sure' are two different things.  I'll check when I can.
When you got the flatter measurements, was the switch perhaps out of the circuit, but in circuit for every other measurement?
When I inadvertently leave it on, depending on which output jack its connected to on the amp, it either crosses over the lows only side from the active or already crossed over mid/high and sounds... very. very. bad. LOL. It's very obvious and I wouldn't have missed it.
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on April 07, 2018, 07:25:53 pm
Well, the answer is whatever was different about the measurement run that generated the spike-less data.
I feel dumb, LOL  I didn't take the EQ out for the run in post 75.  The driver with no EQ applied attached to the horn in the box has the 2-3K slump, and the 7K spike.  I have a strong feeling it's because of the small, non-optimal horn.  Unless I want to make a much larger box to accommodate a better horn, I'm stuck with what I have.  Practicality overrules box size because I don't want to have a much bigger box to haul around for a bass rig.

So, when the active OR the passive X-over is run, without EQ, they both display very similar curves.  A slight improvement might be had to bring the passive response closer to the active response with a re-make of the passive x-over.
But since both crossovers are pretty similar already, the bigger issues - the 7K spike and 2-3K slump - aren't going to be improved with a crossover redesign nearly as much as with the right horn.  Barring that, EQ applied yields greater results.
One thing is for sure, I'm learning a lot from you guys, which is always cool!
Title: Re: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?
Post by: Jeff Schoonover1 on April 08, 2018, 03:52:04 pm
So I was looking at phase shift.  There was quite a bit at the x-over frequency.  I hard-wired the CD out of polarity, which got rid of the phase shift at the x-over frequency.  As a bonus, much of the 2-3K slump was gone.  Now I just had the 7K spike to deal with.  I was able to apply 2 fewer bands of EQ to flatten things than before.  Now I'm only using two bands of EQ, and getting pretty close.
I played around with the X-Over sim quite a bit today.  To really set things right would require a start from scratch.  Resistors aren't practical, because I was seeing as much as 60 watts dissipation necessary to do some of the repairs we talked about.
The 2-3K slump and 7K spike is from the horn I'm using, I'm pretty sure.  To *really* do it right means a new box with a more well-suited horn and a crossover re-make.  A project for another time perhaps, but for a bass rig, it will do for now.  No one listens to the bass player anyway ;)
I sure appreciate everyone's help and suggestions.