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Old 17th January 2014, 01:06 PM   #1
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Default Room Correction with PEQ

Hi guys,

With the availability of cheap and good quality parametric EQs I was wondering if they can be used for room/speaker correction.

I'd like to hear everybody's thoughts on the topic. How can PEQs improve reproduction? Can we improve only a single point or even multiple points? What measurements need to be taken? How do we correlate them to what we hear? How to apply PEQs to mixed-phase responses? Etc. pp.

@Mods: Hope this topic can stay in "Multi-Way" because of visibility and its close relationship to the speaker/room interface.
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Old 17th January 2014, 01:32 PM   #2
pos is offline pos  Europe
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Some interesting documentation on the subject:
using IIR biquads, minimum-phase: Transfer function modeling and equalization by fixed-pole parallel filters
using FIR convolution, arbitrary phase: DRC: Digital Room Correction

PORC implements Bank's minimum-phase method using FIR convolution.

Jlo's Align2 combines both approaches and allows for multiple measurements averaging as well.
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Last edited by pos; 17th January 2014 at 01:47 PM.
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Old 17th January 2014, 01:46 PM   #3
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Originally Posted by pos View Post
Some interesting documentation on the subject:
using IIR biquads, minimum-phase: Transfer function modeling and equalization by fixed-pole parallel filters
Thanks. REW does similar:

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Old 21st January 2014, 02:16 PM   #4
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Unfortunately not much feedback. Is the topic too broad, trivial, out of context?
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Old 21st January 2014, 03:55 PM   #5
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It's a bit broad. What sort of cheap, quality PEQ are you referring to? MiniDSP? Used analog units? You can average a ton of in-room measurements and apply broad, gentle corrections. You can take sets of psuedo-anechoic speaker measurements at different angles to figure out effective speaker correction filters. You can do both.
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Old 21st January 2014, 03:59 PM   #6
Sonce is offline Sonce  Macedonia
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Quote:
Originally Posted by markus76 View Post
How can PEQs improve reproduction? Can we improve only a single point or even multiple points? What measurements need to be taken? How do we correlate them to what we hear? How to apply PEQs to mixed-phase responses?
Enormous improvement! I have tried software PEQ in JRiver and hardware PEQ in Yamaha RXV 2067 and Behringer DCX2469. Nasty low frequency peaks from room modes are easily tamed, also loudspeaker frequency response can be smoothed to the perfection, resulting in very neutral and accurate sound.
Resulting frequency response should be flat to about 1-2 kHz and than slowly down to about -8 dB at 20 kHz. Subjectively that is the most neutral sound.
Multiple point improvement depends heavily on the room acoustics - it can be easy, difficult or impossible. Two subwoofers can help though.
You need some frequency measurement system (ARTA, CLIO or something else) and resolution better than 1/3 octave. RTA (real time analyser) with 1/3 octave resolution is to coarse for room modes.

Please clarify the "mixed-phase response" question, I am not sure what it means.
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Old 21st January 2014, 05:08 PM   #7
mitchba is offline mitchba  Canada
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Agree with Sonce, enormous improvement. Also agree with the target fr. I have used PEQ, DRC that pos linked to and many others.

The best I have found is Acourate, which is not free, but under $400 and well worth it in my experience. With Acourate one can Digital XO, time align, and linearize each driver, plus room correction the fr and excess phase.

I wrote an article about my experience with Acourate: Advanced Acourate Digital XO Time Alignment Driver Linearization Walkthrough.

The linear phase FIR filters produced by Acourate are 64 bit (with 65536 taps) and JRiver's Convolution engine hosts them no problem with the benefit of taking into the account the latency produced by the filter so one can still watch movies with no lip sync issues.

One unique aspect of Acourate is it's measurement analysis uses a proprietary frequency dependent windowing (FDW) algorithm. Having used several acoustical analysis software packages over the years, to my ears, Acourate represents best what I see on the charts compared to what I perceive with my ears. The FDW is long at low frequencies (100ís of milliseconds) and short at high frequencies (< a millisecond).

I have listened to minphase, mixedphase, and linphase FIR filters, and linear phase sounds the best to my ears from an imaging perspective. Subjectively, I would agree with Ackchengs description on his site (3rd paragraph).

Hope that helps. Cheers, Mitch
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Old 21st January 2014, 06:47 PM   #8
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Originally Posted by dumptruck View Post
It's a bit broad. What sort of cheap, quality PEQ are you referring to?
No specific model, miniDSP, Behringer, they all provide filters that are minimum-phase, right?
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Old 21st January 2014, 06:49 PM   #9
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Please clarify the "mixed-phase response" question, I am not sure what it means.
Here's a good read: http://www.dirac.se/media/12044/on_room_correction.pdf
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Old 21st January 2014, 06:51 PM   #10
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Originally Posted by mitchba View Post
Acourate
Yes, great tool. I have it too.
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