ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: 1 [2] 3 4 ... 9   Go Down

Author Topic: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?  (Read 11098 times)

Jeff Schoonover1

  • Full Member
  • ***
  • Offline Offline
  • Posts: 127

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.
Logged

Scott Holtzman

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 5590
  • Ghost AV - Avon Lake, OH
    • Ghost Audio Visual Systems, LLC

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. 
Logged
Scott AKA "Skyking" Holtzman
River Delta Audio is now:

Ghost Audio Visual Solutions, LLC
Cleveland OH
www.ghostav.rocks

David Morison

  • SR Forums
  • Hero Member
  • *
  • Offline Offline
  • Posts: 628
  • Aberdeen, Scotland

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. 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.
Logged

Jeff Schoonover1

  • Full Member
  • ***
  • Offline Offline
  • Posts: 127

So - you guys were right, it was a wiring issue.  The crossover now works as designed.  There is no rattle or distortion.
Logged

Jeff Schoonover1

  • Full Member
  • ***
  • Offline Offline
  • Posts: 127

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. 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.
Logged

Ivan Beaver

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 8866
  • Atlanta GA

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.
Logged
A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Scott Holtzman

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 5590
  • Ghost AV - Avon Lake, OH
    • Ghost Audio Visual Systems, LLC

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
Logged
Scott AKA "Skyking" Holtzman
River Delta Audio is now:

Ghost Audio Visual Solutions, LLC
Cleveland OH
www.ghostav.rocks

Art Welter

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1569

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




Logged

Jeff Schoonover1

  • Full Member
  • ***
  • Offline Offline
  • Posts: 127

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.
Logged

Jeff Schoonover1

  • Full Member
  • ***
  • Offline Offline
  • Posts: 127

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 :)
Logged

ProSoundWeb Community


Pages: 1 [2] 3 4 ... 9   Go Up
 



Page created in 0.027 seconds with 23 queries.