ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: [1] 2 3 ... 9   Go Down

Author Topic: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?  (Read 11096 times)

Jeff Schoonover1

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

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?
Logged

Chris Grimshaw

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1246
  • Sheffield, UK
    • Grimshaw Audio

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.
Logged
Sheffield-based sound engineering.
www.grimshawaudio.com

Jeff Schoonover1

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

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.
« Last Edit: March 19, 2018, 12:41:20 pm by Jeff Schoonover1 »
Logged

Ivan Beaver

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

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

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Jeff Schoonover1

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

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. 
Logged

Scott Holtzman

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

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.

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

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

Stu McDoniel

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1144
  • Central Wisconsin...USA

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.
Logged

Don T. Williams

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 729
  • Midas Pro 1 & 2, M32, dbTech T12, T8, S30, DM12
    • Q Systems Music & Sound

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.
Logged

Jeff Schoonover1

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

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.
Logged

ProSoundWeb Community


Pages: [1] 2 3 ... 9   Go Up
 



Page created in 0.079 seconds with 25 queries.