What's your favorite crossover slope? - Page 2 - diyAudio
Go Back   Home > Forums > Loudspeakers > Multi-Way

Multi-Way Conventional loudspeakers with crossovers

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 3rd October 2004, 06:45 PM   #11
diyAudio Member
 
Join Date: Mar 2003
Location: Denmark, Copenhagen
Default It depends on the variables

Quote:
Originally posted by Ken L

Soooo, I don't think you can say any one slope is best for all situations - it's going to depend on the drivers, the hz, etc., and what method you're using to achieve the crossover function
I agree in this statement

Please don't forget the subject for this thread: "What's your favorite crossover slope?"

It could be interesting to hear what DIY people has as thier favorite crossover slope.

Be free to post what you don't like, but also remember to be constructive!
Hence what about posting your own favorite crossover slope...

Which slope is your favorite crossover slope? And Why?

Regards, Ask
  Reply With Quote
Old 3rd October 2004, 09:08 PM   #12
diyAudio Member
 
Join Date: Aug 2003
Location: Santa Cruz, California
Default Re: It depends on the variables

Quote:
Originally posted by askbojesen


I agree in this statement

Please don't forget the subject for this thread: "What's your favorite crossover slope?"

Which slope is your favorite crossover slope? And Why?

Regards, Ask

My favorite crossover slope starts at about 6 dB/oct, then gradually increases slope until it ends up at 90 dB/oct. It's a Finite Impulse Response (FIR) filter, and the other band is derived by subtracting the filtered signal from a delayed version of the input. I use these for $DAYJOB, and they work marvelously well, especially if you try to keep the filter as short as possible. Longer filters tend to have pre-ringing, which on axis isn't a problem since everything adds up to 1.0 if your drivers are matched at xover frequency, but off axis the pre-ringing creeps in again. The shorter FIRs I design allow about an octave of overlap between the drivers from -1dB to -20dB, but with decent drivers that isn't really an issue. Typically it isn't what your driver does within half an octave of the crossover which kills you, it's what the things do an octave or two into their rolloffs which trash the passband.

For example, a 2500 Hz FIR crossover lowpass filter could be -1dB at 1800 Hz, -6dB at 2500 Hz, -20dB at 3200 Hz, and greater than -60dB at more than 4000Hz. Its HPF dual is -1dB at 3200 Hz, -6dB at 2500 Hz, -20dB at 1800 Hz, and greater than -60dB at less than 1000 Hz. Even though the filters allow some overlap between drivers, they're essentially out of the picture less than an octave into their stopband.

For woofers, you avoid exciting code breakup modes, and excursion is considerably reduced for tweeters. The implications for metal-cone woofers and ribbon tweeters are obvious. You also get phase linearity as a side benefit; it literally drops out of the equation.


Cheers,
Francois.
  Reply With Quote
Old 3rd October 2004, 09:43 PM   #13
diyAudio Member
 
Join Date: Apr 2003
Location: Tampere Finland Europe
Francois,
That sounds interesting, how do you calculate the coefficients for a FIR filter with that kind of slope?
-Mikko
  Reply With Quote
Old 4th October 2004, 01:34 AM   #14
diyAudio Member
 
Join Date: Aug 2003
Location: Santa Cruz, California
Quote:
Originally posted by mhelin
Francois,
That sounds interesting, how do you calculate the coefficients for a FIR filter with that kind of slope?
-Mikko
Well, like John Curl, I can't give *everything* away, because I do need to keep some magic from which I might eventually get product happening, but try looking for a FIR design program which lets you specify the number of coefficients: that'll take you a long way there. Specify an odd number of coefficients, and derive the highpass by subtracting the original signal delayed by (N+1)/2 samples. For example, if your filter is of length 71, then delay the original by 36 samples before subtracting it from the LPF to generate the HPF.

Word length isn't quite as critical for FIRs as it is for IIRs, but you still want 24 bit math at least for nice stopbands.

That should keep you busy for a while....


Cheers,
Francois.
  Reply With Quote
Old 4th October 2004, 08:24 AM   #15
diyAudio Member
 
Join Date: May 2002
Location: Switzerland
Mikko

If you intentionally design a FIR filter with short length you will automatically end up with a filter that is less steep and that will have shorter pre-ringing (in terms of time).

Regards

Charles
  Reply With Quote
Old 4th October 2004, 10:36 AM   #16
diyAudio Member
 
Join Date: Apr 2003
Location: Tampere Finland Europe
Thanks,

If I design a FIR filter using the window method there will be ripple in stopband. If I then use the subtractive method to calculate the HPF the ripple will be in passband, right (or not, is the subtraced response mirrored vertically or horizontally after all)?

Using the Remez method there will be ripple in both pass and stop band, is it any better then? Also which windowing method is best (Kaiser, Hamming or Blackmann, the other are not good I think, Kaiser was recommended somewhere, how about Chebyshev, I think it also looks nice)?
  Reply With Quote
Old 4th October 2004, 12:16 PM   #17
diyAudio Member
 
Join Date: May 2002
Location: Switzerland
I don't remember Francois mentioning that he hasn't any ripple in the stopband !?
I for myself would definitely go for a filter derived by using the windowing method because I want a flat passband.

The stopband ripple looks large on a diagram showing the response in dB but measuerd in volts or what ever it is not much. It will therefore cause a passband ripple in the derived branch that would be best expressed in milli-dB !
The usual way to get FIR higpass parameters using the windowing method is the subtraction of the coefficients of a lowpass from the coefficients of an allpass anyway ! Not much different than the subtractive method mentioned by Francois.


I have to admit thopugh that I am a fan of analogue solutions and I would therefore go for an analog subtractive crossover anyway.

Regards

Charles
  Reply With Quote
Old 4th October 2004, 01:08 PM   #18
diyAudio Member
 
Join Date: Apr 2003
Location: Tampere Finland Europe
So the ripple is there in "subtracted" high pass but it is in the stopband, not in the passband.

So I really need to use convolution only for the LPF, and the HPF output is got by subtracting the delayed input sample from the LPF output sample? In case of 71 point LP kernel it's 71 multiplications and 72 additions (71 MAC's + one add in DSP).
  Reply With Quote
Old 4th October 2004, 06:39 PM   #19
diyAudio Member
 
Join Date: Aug 2003
Location: Santa Cruz, California
Quote:
Originally posted by mhelin
So the ripple is there in "subtracted" high pass but it is in the stopband, not in the passband.

So I really need to use convolution only for the LPF, and the HPF output is got by subtracting the delayed input sample from the LPF output sample? In case of 71 point LP kernel it's 71 multiplications and 72 additions (71 MAC's + one add in DSP).
Most filter CAD programs let you specify passband and stopband ripple. 1dB passband ripple (not what you want to use, really), translates to the subtracted filter having about 20 dB stopband, 0.1dB ripple translates to 40dB stopband, 0.01dB ripple means 60dB stopband, and so on.

Of course the LPF stopband ripple also turns into HPF passband ripple, but I wouldn't worry about 0.01 dB ripple in either case.

And yes, convolving for the LPF and subtracting to generate the HPF is exactly right. You can also do it the other way, if you want, convolving to generate the HPF and subtracting to generate the LPF. That one might be a bit easier if your tool doesn't allow you to plot response from inputted coefficients; you need to do this with the subtracted set to make sure the stopband is behaving, and HPF stopband behaviour is more of an issue if you wish to avoid blowing up tweeters.


Francois.
  Reply With Quote
Old 5th October 2004, 12:10 AM   #20
Ken L is offline Ken L  United States
diyAudio Member
 
Join Date: Sep 2002
Location: deep south
Default Re: It depends on the variables

Quote:
Originally posted by askbojesen

Please don't forget the subject for this thread: "What's your favorite crossover slope?"
Well, I guess I took the liberty of enlarging the thread somewhat, hopefully others won't feel I'm threadjacking _grin_


Quote:
Originally posted by askbojesen
It could be interesting to hear what DIY people has as thier favorite crossover slope.
Most certainly, and why also.


Quote:
Originally posted by askbojesen
Be free to post what you don't like, but also remember to be constructive!
Actually, I thought my post was constructive in addition to being relevant to the thread.

Quote:
Originally posted by askbojesen

Hence what about posting your own favorite crossover slope...

Which slope is your favorite crossover slope? And Why?

Regards, Ask
I don't have a favorite as such but since I'm using NTM 52 db right now, I guess it is my favorite at the moment _big grin_

The Neville Thiele Method slopes are pretty new so I'll post a couple of links

http://www.bss.co.uk/includes/produc...2_include.aspx

In the first one above you'll notice they incorporate a notched response for steeper rolloff.

In this next link, the graphics indicate that a 4th order NTM has steeper roll-off than 4th order L-R.

http://www.fmsystems.net/pdf/cutsheet/fds334t.pdf

while I know that I prefer the NTM 52db slope to the LR 48 DB slope in my current application, I haven't actually done any listening tests to compare the NTM 48DB slope to the LR 48DB.

Regards

Ken L
__________________
No longer powered by Linux - not enough apps and cross platform integration - but maybe one day
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Crossover Slope Question 69stingray Multi-Way 7 26th May 2005 09:21 PM
Crossover slope? Mantronic Multi-Way 0 30th July 2003 02:47 PM
Infinite Slope Crossover thylantyr Solid State 15 21st September 2002 01:36 AM


New To Site? Need Help?

All times are GMT. The time now is 10:18 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2