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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 8th September 2019, 02:00 AM   #2761
BYRTT is offline BYRTT  Denmark
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rePhase, a loudspeaker phase linearization, EQ and FIR filtering tool
Hi chebum,

Think try understand that natural direct sounds in enviroment and also transducers are of minimum phase kind and that sounds perfect and natural as we used to, interference as reflections and difraction are from ground also of minimum phase but in they can take time to arrive it often looks like some kind of linear phase (non minimum phase).

It looks you use linear phase to smooth your transducers direct sound and that is the mistake, if one is sure measurement is of a good quality (direct sound) then use whatever minimum phase EQ filters it takes to smooth transducer, that is when you smooth out (EQ) the amplitude domain you automatic smooth out the phase pattern that belongs to that minimum phase band pass.

Where use of linear phase (FIR) filters comes in, is as a tool to repair the excess phase distortion that happens when we sum multiple minimum phase band passes (XO points) to cover a broad audio band as was it one perfect minimum phase tranducer covering say 20Hz-20kHz.

There is a couple of ways in Rephase to linearize XO point slopes right, one is to first EQ transducer flat as a pancake with whatever minimum phase filters it takes and then in the end add the desired linear phase slope using "Linear-Phase Filters" tab, to get it flat as a pancake also in lows use "compensate" mode on "Minimum-Phase Filters" tab which is a brutal boost at first up until one also set the linear phase filter slope. Second way is to massage tranducer into a smooth minimum phase passband with a known minimum phase slope (stop band), say we set that target slope to be a 700Hz 16th order LR high pass as in your example, then go to "Filters Linearization" tab and pick the known slope to get that known minimum filters huge phase turn linearized.
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Old 8th September 2019, 09:06 AM   #2762
chebum is offline chebum  Poland
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rePhase, a loudspeaker phase linearization, EQ and FIR filtering tool
Many-many thanks for the suggestions. I did a quick testing by changing the eq setting from "linear-phase" to "minimum-phase" and disabled the phase eq completely. Indeed it helped sound a lot.

Quote:
Originally Posted by BYRTT View Post
desired linear phase slope using "Linear-Phase Filters" tab, to get it flat as a pancake also in lows use "compensate" mode on "Minimum-Phase Filters" tab which is a brutal boost at first up until one also set the linear phase filter slope.
Could you describe a bit more what's the difference between linear-filter vs minimum-phase filter + phase correction? For example, if we do both in rephase.
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Old 8th September 2019, 03:14 PM   #2763
BYRTT is offline BYRTT  Denmark
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rePhase, a loudspeaker phase linearization, EQ and FIR filtering tool
Quote:
Originally Posted by chebum View Post
...Could you describe a bit more what's the difference between linear-filter vs minimum-phase filter + phase correction? For example, if we do both in rephase.
Did a general quick description in i have some other stuff to do right now, if you want more info i can get back later today or tomorrow with some how to do it in practical.

In general a difference is that for whatever real world minimum phase filters (IIR) we dial on amplitude response and then phase will always change with a certain pattern belonging to that amplitude and filters can be real time, for linear phase filters (FIR) we can choose dial only amplitude or dial only phase or a mix of both amplitude and phase and using the mix one can actual set a normal IIR filter using FIR tools, FIR filters have some more or less of time lag.

To understand domain of minimum phase see below how a 2nd order butterworth bandpass of 20Hz-20kHz amplitude would look like, phase change 90ļ per order so its a 180ļ turn down at zero Hz and exactly half way 90ļ at -3dB point for the 20Hz 2nd order slope, and same scheme is seen up at HF area for the 20kHz low pass slope, and for example the default flat amplitude and phase we see at start up Rephase is also of minimum phase its just that it has infinite bandwidth from DC (zero Hz) to lightspeed:
rePhase, a loudspeaker phase linearization, EQ and FIR filtering tool-1050a-png

Same amplitude system band pass as above, but in its a sum of two transducers using IIR filtering in a 8th order Linkwitz Riley slope at 700Hz we end up add 720ļ of excess phase turn at 700Hz from that filter:
rePhase, a loudspeaker phase linearization, EQ and FIR filtering tool-1050b-png

Same as above showing the two IIR band passes that sum to above system sum:
rePhase, a loudspeaker phase linearization, EQ and FIR filtering tool-1050c-png

What Rephase is good at same two band passes as above but now phase turn of XO point is linearized so total system phase and amplitude is same as in the very first example:
rePhase, a loudspeaker phase linearization, EQ and FIR filtering tool-1050d-png
Attached Images
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File Type: png 1050b.png (7.5 KB, 287 views)
File Type: png 1050c.png (8.9 KB, 286 views)
File Type: png 1050d.png (8.1 KB, 286 views)

Last edited by BYRTT; 8th September 2019 at 03:17 PM.
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Old 8th September 2019, 05:49 PM   #2764
chebum is offline chebum  Poland
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rePhase, a loudspeaker phase linearization, EQ and FIR filtering tool
Quote:
Originally Posted by BYRTT View Post
Did a general quick description in i have some other stuff to do right now, if you want more info i can get back later today or tomorrow with some how to do it in practical.
I'm sorry for wasting your time with imprecise question. It was obvious to me yesterday, but currently I see I had to be more specific. I'm sorry for this.

I wanted to ask about rephrase options. It allows to create minphase and linear phase filter slopes. Also, it allows to add phase corrections. Will there be any difference between 1) linear phase 24db LR filter and 2) minimum phase 24 db LR filter, created in rephrase, plus phase corrections. Assuming that we create filters using same amount of taps for both options. Both options are strictly fir-based with no iir involved.
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Old 9th September 2019, 12:50 AM   #2765
Oabeieo is offline Oabeieo  United States
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Quote:
Originally Posted by chebum View Post
I have a feeling that FIR-filters "oversharpens" to the sounds. It sounds like particular sounds have contours around them. Similar to what we see on oversharpenned photos from mobile phones. Similar but minimum-phase IIR-filters don't produce these artefacts.

Does anybody hear something similar?

I use rePhase to generate FIR-filters. I suppose I may not be using it correctly. If it's only me hearing the issue, could you check my filter settings? I believe there may be something wrong with my configuration.

Click the image to open in full size.

Click the image to open in full size.


Try using rectangular window with exact centering.
That sounds the best for me.

I canít tell you why (I am still a novice).


That metallic like sound I am familiar with.
Also Iím not sure you need that many taps????
(That I cant speak to but I donít use more than 6144 because I canít and can do just about anything I want)
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Old 9th September 2019, 11:21 AM   #2766
chebum is offline chebum  Poland
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Quote:
Originally Posted by Oabeieo View Post
Try using rectangular window with exact centering.

That sounds the best for me.



Also Iím not sure you need that many taps????
Thank you for the suggestion.
I need that many taps because I'm processing sound with 176400 sampling rate. Actually, it's just 400ms filter. I don't feel it's long enough, because filter slopes at low frequencies aren't precise. Unfortunately, I cannot use longer filters, because the filters are used for home cinema and TV doesn't allow longer delays.
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Old 9th September 2019, 03:15 PM   #2767
wesayso is offline wesayso  Netherlands
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Quote:
Originally Posted by chebum View Post
I wanted to ask about rephrase options. It allows to create minphase and linear phase filter slopes. Also, it allows to add phase corrections. Will there be any difference between 1) linear phase 24db LR filter and 2) minimum phase 24 db LR filter, created in rephrase, plus phase corrections. Assuming that we create filters using same amount of taps for both options. Both options are strictly fir-based with no iir involved.
In theory there should not be any differences between the two. However it can be quite complicated to get it right with indoor measurements. A good LR crossover should not just be the slope you select from a drop down list but rather it should be the measured acoustic slope that follows the chosen LR curve.
The driver(s) itself will have it's own point where the energy falls off. That should all be part of the total combined acoustic slope determining the (named Linkwitz Riley) end result.

If you try to set a linear phase crossover at a certain frequency as with your first option, the driver's own roll off will probably still alter the end result. Unless you can EQ the driver response flat about ~2 octaves past your desired crossover frequency before applying the linear phase crossover.

With the second option it becomes rather difficult to get the right reflection free measurements to base your phase corrections on. Every reflection in such a measurement will alter the phase plot as well (and the FR plot to some extend).

Most of us don't have an anechoic chamber, so we have to search for other ways to get as close as possible. For instance outside measurements, gated measurements etc.
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Last edited by wesayso; 9th September 2019 at 03:18 PM.
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Old 9th September 2019, 04:19 PM   #2768
mark100 is offline mark100  United States
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Quote:
Originally Posted by chebum View Post

I wanted to ask about rephrase options. It allows to create minphase and linear phase filter slopes. Also, it allows to add phase corrections. Will there be any difference between 1) linear phase 24db LR filter and 2) minimum phase 24 db LR filter, created in rephrase, plus phase corrections. Assuming that we create filters using same amount of taps for both options. Both options are strictly fir-based with no iir involved.
I'm trying to add to Wesayso's excellent reply, which matches my understandings and experiences.

As Wesayso said, for making a linear phase 24dB LR, there should be no difference in either technique. You can see this using rePhase...put in a min-phase LR and then use Filters Linearization on it...

His point about needing to EQ a driver response flat extending about 2 octaves past crossover is a biggie imo. The extension needs to be via IIR.

Using IIR EQ, doing this flattening will also flatten the phase roll-off.
If you could get the extension perfectly flat, when you then lay a linear phase xover on top of that IIR correction, the sum of the xover and the IIR EQs will give the exact electrical crossover needed to generate an acoustic xover that matches the lin phase crossover order !
And the crossover doesn't necessarily have to be lin-phase, even with min-phase you still end up with an acoustic order that matches the xover order. Just no flat phase.
Such an easy way to do crossovers.

But of course, extending the rolloff for 2 octaves isn't often doable.
A good solution is extend as far as feasible, and use a higher order crossover that is down 30-40dB before getting out of the flat extension zone.

Hopefully, if anything I've said is amiss, Wesayso, Pos, or someone will correct..
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Old 9th September 2019, 04:47 PM   #2769
Oabeieo is offline Oabeieo  United States
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Quote:
Originally Posted by chebum View Post
Thank you for the suggestion.
I need that many taps because I'm processing sound with 176400 sampling rate. Actually, it's just 400ms filter. I don't feel it's long enough, because filter slopes at low frequencies aren't precise. Unfortunately, I cannot use longer filters, because the filters are used for home cinema and TV doesn't allow longer delays.

:banghead:
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Old 10th September 2019, 08:53 PM   #2770
pos is offline pos  Europe
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Originally Posted by mark100 View Post
But of course, extending the rolloff for 2 octaves isn't often doable.
A good solution is extend as far as feasible, and use a higher order crossover that is down 30-40dB before getting out of the flat extension zone.
The minimum-phase filter "compensate" mode is a good way to obtain this, as noted by BYRTT above.
With care and a proper distance and gating you can often obtain stop-band measurement that are good and usable down to the measurement noise floor.
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