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Multi-Way Conventional loudspeakers with crossovers

rePhase, a loudspeaker phase linearization, EQ and FIR filtering tool
rePhase, a loudspeaker phase linearization, EQ and FIR filtering tool
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Old 26th April 2016, 08:48 PM   #1011
mark100 is offline mark100  United States
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Originally Posted by pos View Post
If your original IIR crossovers are complementary (eg acoustical symmetrical LR) then linearizing the phase will bring the exact same result as if you did build the crossover using acoustical LR slopes with linear phase, on and off axis.

The advantage of going "full-blown" FIR is that you can choose different complementary acoustical filter slopes than the one you could achieve with IIR (overlapping, very steep, asymmetrical, H-K, etc.). It will also be much easier to design, as you noted: phase tracking becomes a lot easier when the only thing you have to shoot for is a flat phase trace, and you also don't have to worry anymore about the effect of one crossover point phase shift on the others.

... and IMHO when applied with a direct convolution FIR is conceptually (and effectively) so much cleaner than a recursive IIR implementation
Yes, thank you POS

Your posts, as much as your program, have helped me see this.
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Old 27th April 2016, 02:04 PM   #1012
mark100 is offline mark100  United States
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Quote:
Originally Posted by pos View Post
If your original IIR crossovers are complementary (eg acoustical symmetrical LR) then linearizing the phase will bring the exact same result as if you did build the crossover using acoustical LR slopes with linear phase, on and off axis.

The advantage of going "full-blown" FIR is that you can choose different complementary acoustical filter slopes than the one you could achieve with IIR (overlapping, very steep, asymmetrical, H-K, etc.). It will also be much easier to design, as you noted: phase tracking becomes a lot easier when the only thing you have to shoot for is a flat phase trace, and you also don't have to worry anymore about the effect of one crossover point phase shift on the others.

... and IMHO when applied with a direct convolution FIR is conceptually (and effectively) so much cleaner than a recursive IIR implementation
Hi POS, ..like I said, I am seeing the equivalence you speak of in the two methods ....for electrical filters.

What I'm still wrestling with is, can equivalence exist for correcting the drivers' acoustical phase response too?
IOW, I know each driver has an inherent acoustical phase curve. Can their summed phase responses be flattened, or must each driver be flattened individually?

I guess the real question is, does acoustical phase summing even exist?
Or is it that waves stay separate in phase, but sum in magnitude based on their varying separation?

I can see there is magnitude summing depending on phase angle, I just can see what phase summing means....or how you could flatten 'what I'm wondering if even exists'
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Old 27th April 2016, 02:28 PM   #1013
pos is offline pos  Europe
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Hi Mark

In a properly implemented acoustical LR crossover both acoustical filters are perfectly complementary and sum to a flat magnitude response (on axis at least).
When temporally aligned each driver encounters the same phase shift, which is also reflected as an allpass in the final summed response. This is called phase tracking and means the two drivers are in phase with each other.
If you then "linearize" the phase of that summed response with an inverse allpass you get a perfect linear phase crossover, exactly identical to what you would get with two linear phase "LR" acoustical filters.

But getting a perfect phase tracking is not that easy in practice when you have several crossover points, because of the influence of other crossover points. In this situation you have to "replicate" lower filters as if the crossovers were chained (cf Linkwitz link I posted a few posts above).
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Old 28th April 2016, 04:42 AM   #1014
Osse is offline Osse  Sweden
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Hi again, thank you for your response mark100! Have you tried to globally correct the phase incoherency with your soundsystem aswell? Would be awesome to hear your reports and findings if it benifits your system.

Right now I'm using Keystone tapped horns which are really good, but they have a bit of phase shift and I wonder how they would sound corrected and with IIR filters phase corrected out aswell.

Last edited by Osse; 28th April 2016 at 05:09 AM.
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Old 28th April 2016, 04:32 PM   #1015
mark100 is offline mark100  United States
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Quote:
Originally Posted by pos View Post
Hi Mark

In a properly implemented acoustical LR crossover both acoustical filters are perfectly complementary and sum to a flat magnitude response (on axis at least).
When temporally aligned each driver encounters the same phase shift, which is also reflected as an allpass in the final summed response. This is called phase tracking and means the two drivers are in phase with each other.
If you then "linearize" the phase of that summed response with an inverse allpass you get a perfect linear phase crossover, exactly identical to what you would get with two linear phase "LR" acoustical filters.

But getting a perfect phase tracking is not that easy in practice when you have several crossover points, because of the influence of other crossover points. In this situation you have to "replicate" lower filters as if the crossovers were chained (cf Linkwitz link I posted a few posts above).
Hi Pos,
Thx. Read the Linkwitz link and understand the influence of other crossover points...like you say, all the more reason for linear-phase crossover filters.
I'm pretty familiar with phase tracking...been using smaart to align phase traces, subs to main, for a while.
All in all, electrical crossovers are making sense....no real difficulty there..

I'm still not quite so clear with the mechanical part....ie the drivers' raw acoustic response....and corrections for these responses.

I have a hard time seeing how a global correction can correct the phase of each driver individually, through the x-over region. I can see how global can correct the summed response easy enough..
But it still seems like a summed correction is suboptimal to having each of the drivers flattened first..

Sorry for being so dense....
But hey, I really do think I get compensate now
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Old 28th April 2016, 04:54 PM   #1016
mark100 is offline mark100  United States
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Quote:
Originally Posted by Osse View Post
Hi again, thank you for your response mark100! Have you tried to globally correct the phase incoherency with your soundsystem aswell? Would be awesome to hear your reports and findings if it benifits your system.

Right now I'm using Keystone tapped horns which are really good, but they have a bit of phase shift and I wonder how they would sound corrected and with IIR filters phase corrected out aswell.
Hi Osse, no I haven't tried global correction yet....intend to though...still sorting out understanding how it works as you can tell

I'm using Labhorns and JTR OS subs, also horn loaded. Correcting the IIR filters is easy enough, although correcting a HP takes a lot of taps and latency. I haven't tried to correct the subs acoustic response yet.
All my effort so far has been directed at a DIY main...here's a post i made yesterday in another forum re progress on it...https://soundforums.net/threads/1207...l=1#post100676 Also, more comments about latency a couple of posts below...
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Old 28th April 2016, 05:30 PM   #1017
Osse is offline Osse  Sweden
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Originally Posted by mark100 View Post
Hi Pos,
Thx. Read the Linkwitz link and understand the influence of other crossover points...like you say, all the more reason for linear-phase crossover filters.
I'm pretty familiar with phase tracking...been using smaart to align phase traces, subs to main, for a while.
All in all, electrical crossovers are making sense....no real difficulty there..

I'm still not quite so clear with the mechanical part....ie the drivers' raw acoustic response....and corrections for these responses.

I have a hard time seeing how a global correction can correct the phase of each driver individually, through the x-over region. I can see how global can correct the summed response easy enough..
But it still seems like a summed correction is suboptimal to having each of the drivers flattened first..

Sorry for being so dense....
But hey, I really do think I get compensate now
I'm kinda trying to wrap my head around the same questions, however if you don't overlap drivers freq range and compensate for the crossover, and then globally linearize the phase over the whole system it should be close to perfect would be my guess. Isn't the combination of driver/cabinet phase shift more important to consider than the drivers phase shift alone?

However, if you linearize the phase on each cabinet/driver individually, could they overlap without phase issues?

Are you supposed to isolate the crossover/cabinet from the spatial room and get it perfect, and use the same settings in every room or is the room part of the equation?

Nice selection of subs you have got there, heard a lot of good stuff about both the OS and the Labhorn. I've used BFM T30's for a few years and a thousand or two hours by now and they are great for what they do but I wanted to make the switch for fewer/more powerfull cabinets... And I can say that 2 keystones I recently built with premium drivers are around twice as loud as 4 almost full-sized T30's with premium drivers, non-scientific opinion offcourse.

Does it take a lot of taps/latency due to the low frequency of the HP on the subs?

Edit: Oh you are building the diy 60 cabinet! I've been following that thread with interest. Awesome system you gotta have there, what music do you generally punish it with?

Last edited by Osse; 28th April 2016 at 05:43 PM.
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Old 28th April 2016, 06:21 PM   #1018
mark100 is offline mark100  United States
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Quote:
Originally Posted by Osse View Post
I'm kinda trying to wrap my head around the same questions, however if you don't overlap drivers freq range and compensate for the crossover, and then globally linearize the phase over the whole system it should be close to perfect would be my guess. Isn't the combination of driver/cabinet phase shift more important to consider than the drivers phase shift alone?

However, if you linearize the phase on each cabinet/driver individually, could they overlap without phase issues?

Are you supposed to isolate the crossover/cabinet from the spatial room and get it perfect, and use the same settings in every room or is the room part of the equation?

Nice selection of subs you have got there, heard a lot of good stuff about both the OS and the Labhorn. I've used BFM T30's for a few years and a thousand or two hours by now and they are great for what they do but I wanted to make the switch for fewer/more powerfull cabinets... And I can say that 2 keystones I recently built with premium drivers are around twice as loud as 4 almost full-sized T30's with premium drivers, non-scientific opinion offcourse.

Does it take a lot of taps/latency due to the low frequency of the HP on the subs?

Edit: Oh you are building the diy 60 cabinet! I've been following that thread with interest. Awesome system you gotta have there, what music do you generally punish it with?
I think there is always more overlap that we might guess...for instance, a LR48 (which i view as steep) set at 100hz for both sides, will sum from 60hz to 200hz.

I know you can linearize the filter effect globally.
And I know you can additionally linearize the driver's natural responses individually...still working on this globally

The plots you saw on my DIY60 link are individually corrected drivers, which definitely overlap.

Room correction? Ugh...I don't believe in it...or shall I say it only works for one position.
Acoustic solutions for acoustic problems...speaker placement..room absortion..diffusion...etc.... these solutions work, but my experience is we are chasing our tail with electronic room correction...

Art's keystones are great huh. I was looking for a project and came close to building a pair before I jumped on the DIY60. And I guess I already had too much sub power.

Yes, numbers of taps (which means latency to me) goes up fast with lower freq.

Music? I play about everything, still have a kid in college, and I'm in my 60's...so everything.
Almost impossible to punish the DIY60...it is one powerful box. It's my poor neighbors that take the punishment,
...or at least until I take it when the cops show up
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Old 28th April 2016, 06:56 PM   #1019
pos is offline pos  Europe
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Originally Posted by mark100 View Post
I have a hard time seeing how a global correction can correct the phase of each driver individually, through the x-over region. I can see how global can correct the summed response easy enough..
But it still seems like a summed correction is suboptimal to having each of the drivers flattened first..
When you have an in-phase complementary minimum-phase acoustical crossover both drivers have the exact same phase shift throughout the crossover.
Once you are there, if you were to correct those drivers to get linear phase acoustical filters for each of them, you would use the exact same correction for both. Hence you can as well put that correction on the input and the result will be identical.
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Old 28th April 2016, 07:53 PM   #1020
mark100 is offline mark100  United States
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Originally Posted by pos View Post
When you have an in-phase complementary minimum-phase acoustical crossover both drivers have the exact same phase shift throughout the crossover.
Once you are there, if you were to correct those drivers to get linear phase acoustical filters for each of them, you would use the exact same correction for both. Hence you can as well put that correction on the input and the result will be identical.
Thx for bearing with me POS

Maybe this will help you see what i'm am missing...

Below are the HF driver (top) and MF (bottom).
Each have a couple of para eqs for a little amplitude smoothing.
They also have linear-phase 48db LRs at 100 & 650, and 650 & 6300.
I know the linear-phase crossovers did not effect phase on either.
Nothing else was done , the corrections (windowing, taps, sample etc) are not what I'm using, just a quick throw together for illustration's sake.

If I look at say 700hz on each, where summation is taking place....
on the HF, I see about 95 deg phase
on the MF, I see about 3.

So about 90 degrees diff, which gives maybe around 3db summation.
OK, so i go measure combined response and easily add para eq to flatten...
But if I adjust phase at 700, what am i adjusting..wouldn't I be moving both drivers the same number of degrees, when i really want to bring them together?
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Last edited by mark100; 28th April 2016 at 07:58 PM. Reason: keep realizing i misread values from graphs
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