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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 13th February 2018, 03:01 PM   #2401
pos is offline pos  Europe
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Quote:
Originally Posted by scottjoplin View Post
I thought that's what "room EQ" meant when talking about DSP?
Room EQ typically address the interaction between the loudspeaker and the room from the listening position(s). It can also address defects from the loudspeaker itself in the process.
The cleaner the setup (ie symmetrical placement, acoustically treated room, bigger room, etc.) the less room EQ you should need.

Speaker EQ is more intended at addressing the defects of the loudspeaker itself, regardless of the room it will be installed in. This is for example what JBL/Harman does with their spinorma approach.
This type of EQ can be done in room, but special care has to be taken to isolate what comes from the room (at the measurement position) and what comes from the speaker.

You can probably do both in the same time, but I think it is always better to start with speaker EQ and add room EQ if/where needed (ideally only for LF if the setup is OK and the speaker has a well behaved off axis response)
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Old 13th February 2018, 03:08 PM   #2402
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Quote:
Originally Posted by arcgotic View Post
Regarding number of taps. I created them using defalult value I think, 64k something like that. Is there a 'best' value? I did not see any significant increase in CPU load.
1sec of FIR (eg 44.1k taps at 44.1kHz and 192k taps at 192kHz) is generally more than enough for any kind of real world correction.
(By the way what convolution software are you using? You need to resample everything to the sampling frequency of the FIR, or have specific FIRs for each possible sampling frequency)

If CPU is not the limiting factor then you have to consider what delay you can accept.
1sec FIR with middle centering will impose 0.5s of delay.
Of course if you mostly use minimum-phase correction (which is often the case), then you can reduce that delay by lowering the centering (eg "1%" when doing exclusively minimum-phase correction, which result in 1ms of delay for a 1sec FIR).

Also, in you situation you can avoid using the "optimization" feature: it is very useful when you are tap-limited, but can generate pre ringing.
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Old 13th February 2018, 03:28 PM   #2403
arcgotic is offline arcgotic  Romania
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I use EqAPO. It requires 192khz sampling rate impluse file (I think because the Asus PCI soundcard is set to 192).
I don't mind the delay, I can adjust in the video player the sound also (Kodi).

Middle centering setting also has impact on pre ringing?
I will use 'no optimization', thanks for the tip.
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Old 13th February 2018, 07:48 PM   #2404
pos is offline pos  Europe
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Nope, no impact on preringing per se, but less truncation, which is a good thing.

Please note that the 1sec FIR suggestion is on the high side, to be able to cope with all situations: you probably don't need that much most of the time in practice.
My advice would be to use just enough taps for the task, ie the number of taps for which you get satisfying result curves (ie matching the target ones close enough) without having to resort to optimization.
Also you should use the same number of taps for all your channels (ie the numbers of taps required for the lower channels, because LF typically requires more taps) to avoid delay problems (FFT engines can be tricky, and simple delay compensation with different tap counts might not give predictable results)

Oh, and a small typo caught my eye in my last post (too late to edit)
Quote:
Originally Posted by pos View Post
(eg "1%" when doing exclusively minimum-phase correction, which result in 10ms of delay for a 1sec FIR)

Last edited by pos; 13th February 2018 at 07:53 PM.
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Old 13th February 2018, 08:53 PM   #2405
arcgotic is offline arcgotic  Romania
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Aha, thanks! (I need to learn more before I understand!)

I am thinking for next release, is it possible that each time we generate an impulse file *.wav, an *.rephase with the same settings is saved?

This can be useful, I forget to save last night my Paragraphic phase EQ and the rest, and if i just want to change the xo point I need to redo all other settings.
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Old 14th February 2018, 07:59 AM   #2406
torgeirs is offline torgeirs  Norway
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Super recomendations, pos!

Wonder if DRC can be used to precorrect each driver, if also time corrections are needed?
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Old 14th February 2018, 08:11 AM   #2407
scottjoplin is offline scottjoplin  Wales
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Under what circumstances and frequency range is DRC useful?
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Old 14th February 2018, 11:56 AM   #2408
torgeirs is offline torgeirs  Norway
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I speculate if it is usefull in cases where you have reflections back to the driver inside a box or standing waves inside the box. Or maybe diffraction on the front plate.
DRC is used with success outside the box (in the room). Just speculating if it can be as good with refelections and standing waves inside the box.
Further flattening of phase and amplitude and xover filtering can then be done by rePhase FIRs summed with the DRC FIR.
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Old 14th February 2018, 12:05 PM   #2409
scottjoplin is offline scottjoplin  Wales
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I see, interesting, I presumed you meant outside the box, in the room, for obvious reasons .
Under what circumstances in the room has/is it used successfully? I understand it is still in its infancy and wonder how effective it is and how it differs from other attempts at digital room EQ
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Old 14th February 2018, 01:59 PM   #2410
torgeirs is offline torgeirs  Norway
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Thinking of Denis Sbragion's DRC:
DRC: Digital Room Correction

Has been around for a while:-)
And Denis says it works best at close reflections.
The "stolen idea" is to correct speaker elements well into the xover region to try to make the two elements be acoustically in phase in the overlapping region. And thus be in accordance with linkwitz-reilly requirement of 0 phase difference between drivers through xover region (3 octaves). Puh. Maybe over complicating things:-)
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