Aren't 4th order LR crossovers supposed to pass squarewaves? - diyAudio
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Old 24th November 2004, 05:48 PM   #1
Bricolo is offline Bricolo  France
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Default 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
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Old 24th November 2004, 05:50 PM   #2
SY is offline SY  United States
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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.
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Old 24th November 2004, 05:50 PM   #3
pxr5 is offline pxr5  United Kingdom
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you output will look nothing like a square wave.
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Old 24th November 2004, 05:53 PM   #4
pxr5 is offline pxr5  United Kingdom
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from memory i think its only summed 1st order which will. google search and some typical results will be found
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Old 24th November 2004, 05:55 PM   #5
pxr5 is offline pxr5  United Kingdom
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also this is 1st order INCLUDING speaker driver transfer function, generally the higher the order the less like a square wave
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Old 24th November 2004, 05:56 PM   #6
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Default 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.
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Old 24th November 2004, 06:04 PM   #7
pxr5 is offline pxr5  United Kingdom
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I'm am misconceived
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Old 24th November 2004, 06:05 PM   #8
Davey is offline Davey  United States
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Default Re: Aren't 4th order LR crossovers supposed to pass squarewaves?

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.
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Old 24th November 2004, 06:28 PM   #9
Bricolo is offline Bricolo  France
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OK, thank you guys. I was mistaken...
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Old 24th November 2004, 06:53 PM   #10
hifi is offline hifi  Sweden
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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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