Aren't 4th order LR crossovers supposed to pass squarewaves?

Bricolo · 24th November 2004, 05:48 PM

Hi,

Here's my problem: I'm working on an active crossover project, and have just tested the LR4 alignment.
I thought that LR4 were supposed to pass squarewaves correctly (the summed output should be a squarewave), but mine doesn't

What's wrong?

Here's the (simplified) topology.
I think it's a LR4 alignment, since Q of one stage is 1/(3-Gain) and gain=1.58. Q=0.707 (butterworth)
2 cascaded 2nd order butterworth form a LR4

http://www.diyaudio.com/forums/attac...amp=1101235143

input signal (red), the low pass output (green) and high pass output (blue)
http://www.diyaudio.com/forums/attac...amp=1101234956

And here's the summed output

http://www.diyaudio.com/forums/attac...amp=1101235302

Thanks for help

SY · 24th November 2004, 05:50 PM

Quote:

I thought that LR4 were supposed to pass squarewaves correctly (the summed output should be a squarewave)

I don't think that's true.

pxr5 · 24th November 2004, 05:50 PM

you output will look nothing like a square wave.

pxr5 · 24th November 2004, 05:53 PM

from memory i think its only summed 1st order which will. google search and some typical results will be found

pxr5 · 24th November 2004, 05:55 PM

also this is 1st order INCLUDING speaker driver transfer function, generally the higher the order the less like a square wave

Henrik Juhl · 24th November 2004, 05:56 PM

Bricolo,

Neither do I think the throughput should be square

Have you seen this article about 'transient perfect' filters?

http://www.geocities.com/kreskovs/CrossoverdocN.html

See also his main page on: http://www.geocities.com/kreskovs/John1.html

Some foods for thought and very inspiring.

pxr5 · 24th November 2004, 06:04 PM

I'm am misconceived

Davey · 24th November 2004, 06:05 PM

Quote:

Originally posted by Bricolo

What's wrong?

Nothing. Your simulation results look correct to me. LR4 crossovers, as well as many other, won't sum and reproduce a square wave identical to the input. This is normal.

Cheers,

Davey.

Bricolo · 24th November 2004, 06:28 PM

OK, thank you guys. I was mistaken...

hifi · 24th November 2004, 06:53 PM

bessel are suppose to pass square waves pretty well since they feature a flat groupdelay in the passband so not to delay any of the squares harmonics.

24th November 2004, 05:48 PM	#1
Bricolo diyAudio Member Join Date: Nov 2002 Location: Grenoble, FR	Aren't 4th order LR crossovers supposed to pass squarewaves? Hi, Here's my problem: I'm working on an active crossover project, and have just tested the LR4 alignment. I thought that LR4 were supposed to pass squarewaves correctly (the summed output should be a squarewave), but mine doesn't What's wrong? Here's the (simplified) topology. I think it's a LR4 alignment, since Q of one stage is 1/(3-Gain) and gain=1.58. Q=0.707 (butterworth) 2 cascaded 2nd order butterworth form a LR4 http://www.diyaudio.com/forums/attac...amp=1101235143 input signal (red), the low pass output (green) and high pass output (blue) http://www.diyaudio.com/forums/attac...amp=1101234956 And here's the summed output http://www.diyaudio.com/forums/attac...amp=1101235302 Thanks for help __________________ Just remember: in theory there's no difference between theory and practice. But in practice it usually is quite a bit difference... Bob Pease

24th November 2004, 05:56 PM	#6
Henrik Juhl diyAudio Member Join Date: Apr 2003 Location: Copenhagen	Not square. Bricolo, Neither do I think the throughput should be square Have you seen this article about 'transient perfect' filters? http://www.geocities.com/kreskovs/CrossoverdocN.html See also his main page on: http://www.geocities.com/kreskovs/John1.html Some foods for thought and very inspiring. __________________ Regards, Henrik Juhl

24th November 2004, 06:28 PM	#9
Bricolo diyAudio Member Join Date: Nov 2002 Location: Grenoble, FR	OK, thank you guys. I was mistaken... __________________ Just remember: in theory there's no difference between theory and practice. But in practice it usually is quite a bit difference... Bob Pease

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24th November 2004, 05:50 PM	#3
pxr5 diyAudio Member Join Date: Jul 2004 Location: england	you output will look nothing like a square wave.

24th November 2004, 05:53 PM	#4
pxr5 diyAudio Member Join Date: Jul 2004 Location: england	from memory i think its only summed 1st order which will. google search and some typical results will be found

24th November 2004, 05:55 PM	#5
pxr5 diyAudio Member Join Date: Jul 2004 Location: england	also this is 1st order INCLUDING speaker driver transfer function, generally the higher the order the less like a square wave

24th November 2004, 06:04 PM	#7
pxr5 diyAudio Member Join Date: Jul 2004 Location: england	I'm am misconceived

24th November 2004, 06:53 PM	#10
hifi diyAudio Member Join Date: Mar 2001 Location: sweden	bessel are suppose to pass square waves pretty well since they feature a flat groupdelay in the passband so not to delay any of the squares harmonics.

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