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Why You Need Room Correction

Discussion in 'Room Acoustics, Audio & Video Calibration' started by Rob Sinden, Jun 1, 2009.

  1. Rob Sinden

    Rob Sinden Active Member Assured Advertiser

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    Regardless of how terrific your audio equipment is and how perfectly your room has been designed, your room will still create significant distortion.

    I have just spent over £25,000 on the acoustic design and fit out of my purpose-built listening room and I can assure you that even this “perfect space” still needs room correction.

    Room correction is an incredibly powerful tool that, if used correctly, will significantly reduce the errors your room creates leaving a much higher fidelity audio system.

    The Goal of Room Correction

    Like acoustics, the area of room correction is a huge and very complex one; however some principals can be easily understood.

    The key principle behind room correction is to try and remove the negative effect that your room has had on your system. In its most basic form this is done by reducing the sounds that your room exaggerates so that what is heard at the listening position is much closer to the sound that left your speakers.

    Types of Room Correction

    The 3 main types of Room Correction are Graphic Equalisers, Parametric Equalisers and Full Range Automated Systems.

    These days Graphic Equalisers are rarely used because they do not provide the resolution required to correct the very specific errors that different rooms create.

    Parametric Equalisers have been available for years and are now common on many products such as Velodyne Subs & SMS units, Sunfire Signature Subs and Yamaha electronics. These products use simple parametric equalisers to reduce a small number of the worst peaks that your room has created. Some surround processors from Meridian and Lexicon use higher resolution parametric equalisation but these systems are still limited to reducing just the most obvious bass errors that your room creates.

    While Parametric EQ’s are a low resolution solution to a high resolution problem, they can still significantly reduce the boominess that is so common when large speakers and subwoofers are used in most rooms.

    Full Range Automated Systems

    One of the biggest developments in home audio has been the arrival of room correction systems that address all the frequencies that you can hear.

    To correct the acoustic problem that your room creates, first you must measure a three dimensional space and analyse 20,000 different frequencies arriving directly and by reflections, for level, power response and timing. If this sounds like something that you can fix manually, you haven’t understood the problem!

    Now that computers have the processing power to assess and analyse the huge quantity of data required to understand your room’s acoustic problems, we have some hope of correcting them.

    Currently there are two automated, full range room correction systems for the home. One is intended for stereo use and the other for surround sound. Used correctly, these room correction systems will absolutely, categorically improve the sound of your audio system, even in the best designed room.

    If you are serious about achieving the best sound quality you can, make sure you choose a dealer who has a solid foundation in acoustics and a proven method of reducing the errors your room will create. Without being able to understand and fix the acoustic problem that your room WILL create, your dealer simply will not be able to remove these errors and so cannot install an accurate sound system for you.

    The Results

    Using sub/sat speakers, professional room design and room correction will provide more accurate sound reproduction than any alternatives. Typically this approach also produces much more affordable, discreet systems.

    If you found this post helpful you may be interested in some of the other topics I've posted on:
    - Why Good Audio Equipment Sounds Bad
    - Professional Recommendations for Surround Sound Design
    - The Benefits of Room-Friendly Speakers
    - Acoustic Room Design
    - The Result of Professional System Design
    Last edited: Jun 1, 2009
  2. Member 639844

    Member 639844 Former Advertiser

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    Good post, explains why devices like the antimode 8033 etc etc are important. Ive been into AV for as long as I can remember, but its only the last year or so Ive picked up on the points you post here.

    This could save new comers a lot of time. :smashin:
  3. Amioa

    Amioa Member

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    Id really like to do some subjective testing to see what people prefer in a blind test, electronic correction of bass or passive treatments.
  4. Rob Sinden

    Rob Sinden Active Member Assured Advertiser

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    I'd love to help. You can use our facilities anytime and here you have 4 systems that utlise the worlds most advanced room correction systems to do A/B comparisons with.
    Let me know what you need to make it happen.
  5. Member 639844

    Member 639844 Former Advertiser

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    or both :thumbsup:
  6. Amioa

    Amioa Member

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    yes indeed, or both! Rob I may be intouch about that.
  7. Rob Sinden

    Rob Sinden Active Member Assured Advertiser

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    I'm waiting...........
  8. Amioa

    Amioa Member

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    you can wait until tomorrow :D
  9. dj-dulux

    dj-dulux Member

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    I would also be interested in that.....

    Dupe...
  10. Amioa

    Amioa Member

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    sorry guys, been out all day doing consultant related stuff, I will get in contact Rob, I need to have a think about how to approach this
  11. Rob Sinden

    Rob Sinden Active Member Assured Advertiser

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    Me too. Bloody customers!

    Let me know what you have in mind or perhaps it would be quicker if we have a chat if that isn't against some rule or other? It'll be great for someone to put my claims to the test!

    Cheers

    Rob
  12. dj-dulux

    dj-dulux Member

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    I had a little demo yesterday of a room correction system, following that, I think we need to study the phase information as well as the frequency. I felt that some of the transient response was lost once the correction system was introduced and feel that this was likely due to phase shifts being introduced within the processing smearing the signals.

    I think if we artificially generate some transient signals (simulation of gun shot for example) we can see the effect of correction system using objective measures and with a bit of blind testing (A-B comparison stuff) we will hopefully be able to prove that the transient response is in fact affected or not and matters or not?

    How this then relates to subjective impression will be interesting, for what ever reason most systems focus purely on frequency response. In my opinion his is only part of the problem.

    Its a start.

    Dupe...
    Last edited: Jun 4, 2009
  13. Rob Sinden

    Rob Sinden Active Member Assured Advertiser

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    Great. That's what it's all about isn't it. Listening and seeing if the different systems actually work.

    I first used Audio Control graphic equalisers around 12 years as they were highly recommended in US specialist press. These added loads of noise to the system and made things a lot worse.

    I think if people are interested in the subject then you quickly realise that much higher resolution is required than is available with most units. An 8 band parametric EQ isn't much help when you're dealing with 20,000 frequencies in a three dimensional space.

    This is why computers are often needed because of the sheer quantity of data that needs collecting, evaluating and correcting.
  14. Capoerista

    Capoerista Member

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    Hi everyone,

    I'm rather a newbie to the audio department, so please bear it in mind if you find my problem lame.

    My room is 2,5 by 4 m and I'm using basic computer speakers hooked up to a PC, which I use mostly for playing DVDs. The problem is that I have a pretty powerful subwoofer as well, at least for such a small room, which goes into resonance every now and then. It happens for certain frequencies I guess, since I can watch some 'bassy' films with virtually no hiccups, other times the whole room is shaking even at low volume, which can be painful to the ears.

    So my question is: are there any software solutions for the PC to locate and eliminate those peak frequencies that cause resonance?

    I can't afford a dedicated hardware to do the job. Is there a program that can test the frequencies in a given range? I could hear the ones that produce resonance and tell the program to dampen these. This would be just for the subwoofer (up to maybe 100 Hz), so not that much hassle I hope. Is it possible? Or is there any other, non-costly solution to my problem?

    Thanks in advance for your help.
  15. Rob Sinden

    Rob Sinden Active Member Assured Advertiser

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    I know Craig tried some free programmes which he said were some help. I'm sure some of the members here will come up with some ideas.
    Ordinarily I would start with seeing if repositioning the sub helps but I would imagine being part of a PC set up it plays 200Hz and so must be kept central to the main speakers. Is there any adjustment for the level on it or in your PC. They nearly always play too loud which I suspect is the biggest problem?
  16. Capoerista

    Capoerista Member

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    Hi,

    The sub is placed 0,5 m from a wall (to the side and back), and due to room constraints repositioning it is rather hard.

    Software-wise, I'm using X-Fi drivers and AC3 filter for audio processing. I'm not employing any bass boost or equalisers for lack of resolution. But the remote to the speaker system has a separate dial for continuous sub control. It's usually set at 40-60%, and as I mentioned sometimes it's low on volume and maybe 30% bass and an unpleasant resonance can be heard nonetheless.
  17. Rob Sinden

    Rob Sinden Active Member Assured Advertiser

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    The only thing I can suggest that isn't too expensive but should proove helpful is a parametric eq devise from Berhinger. BEHRINGER: Home

    Can any of the guys with a professional background recommend anything else?
  18. Member 639844

    Member 639844 Former Advertiser

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    Which one did you demo? FYI they arent all the same, the Velodyne SMS-01 for example doesnt take the time domain into account, but the Antimode 8033 SVS AS-EQ1 both do.

    This may well be the difference. It has been suggested that non-time domain devices strive to get a flat response, while the time domain ones can leave you with a less than flat response that actually sounds flatter because its fixing phase issue and ringing effects. Also the effect you describe is quite common among people using in built auto EQ systems, although not everyone agrees. I guess preference comes into it.

    FYI (and this is for Rob too), I use on board Audyssey Multi EQ XT auto eq, as well as REW and my subs on board tuning options to help EQ my system. My sub uses an on board single band PEQ, 3 tuning modes, room comp adjustment and a variable phase control to help with manual EQ'ing. Ive found the combination of the amp and sub when EQ'd does improve my sound wthout removing any of the feeling from music. Add to some room improvements ive added and it's not a bad result if I say so myself.

    That said my system is a good deal further down the pecking order compared to what Rob is running.
    Last edited by a moderator: Jun 5, 2009
  19. Member 639844

    Member 639844 Former Advertiser

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    I dont have a pro background but there are a few devices avaiable. The BFD used with something like REW is useful and cheap but not perfect and there are a few auto options available that are quite a bit better.

    The dspeaker antimode 8033 (around £250)
    The Velodyne SMS-01 (around £400)
    The SVS AS-EQ1 (around £650)

    I think there are a couple others but I cant think of them just now. Also some of these are a sub only EQ device, but some will look at your speakers too.

    Of course there are subs like the JL Audio Fathom subs that have built in auto EQ as well :smashin:
    Last edited by a moderator: Jun 5, 2009
  20. dj-dulux

    dj-dulux Member

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    Don't want to say just yet, but it knocking on the door of £10k, they are going to lend me one to do a bit more testing. It is the best attempt at room correction I have heard so far, although I should pop to Robs and have a listen at his kit.

    I would think its very difficult to correct for phase (and hence time) shifts in the processor, you would need a very DSP set up to correct in real time for all the filters that are applied. Just to clarify I am not talking about setting overall delays for speaker distance correction.

    Dupe...
  21. Member 639844

    Member 639844 Former Advertiser

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    Dolby Lake perhaps? Although I believe its being discontinued so perhaps not.

    I know what your not talking about though mate :smashin:. I look forward to your future post on this.
  22. craigd

    craigd Member

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    I have indeed. Unfortunately the more advanced of the free programs are very technical (e.g. Duff Room Correction) and you still need access to a calibrated mic.

    As a start a copy of this:

    Room EQ Wizard Home Page

    And a good EQ plug-in to winamp/windows media player would help. In fact you may get somewhere without a mic. Room EQ Wizard with generate sine waves of a particular frequeny. You can use its signal generator to move through the bass region and you should be able to hear when you hit a resonance. You can then use the EQ plug-in to reduce it.
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  23. Piers

    Piers Member

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    Rob,

    Agreed that the Behringer is a useful piece of kit but it is butt-ugly and this has prevented my using it on a couple of installs where it would have delivered good results.

    I suspect that I heard the same device yesterday as dj-dulux ... but maybe not ;) Very impressive and I too am getting one to play with. More expensive than the Audyssey EQ Pro and A/B testing will be interesting.

    Gerry Lemay (Mr. HAA!) pointed me towards a QSC DSP-4 last year when I was looking for a parametric equaliser for a client. Sadly, the guy who answered the phone at the UK Distributor's totally failed to understand why I wanted one, and as I wasn't using QSC amps he talked me out of buying one.
  24. Amioa

    Amioa Member

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    If you dont mind me asking, is the choice of using Digital correction to treat room issues client driven, budget driven or just a personal preference?
  25. Neil Davidson

    Neil Davidson Active Member Assured Advertiser

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    If you guys haven't tried the Trinnov yet then you should do so - it is excellent and will soon be available in a more CI friendly form from ADA.

    The Audyssey is excellent but of course benefits from excellent technique making the measurements. The balanced and unbalanced sound pretty similar but the balanced has much more headroom which is needed when playing with the big toys.

    Dolby sold the Lake brand and IP to Lab Gruppen who sadly stopped production of the standalone Lake Processor. You can see one of those amazing devices in the one of my high end videos over at AVForums.tv. The Lake is without doubt the best sounding DSP device so far but it is very different from the other two units as it is 100% manual calibration.

    We remain hopeful that there may be something new on the Lake front later this year though...
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  26. Piers

    Piers Member

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    Amioa,

    Good question.

    Physical correction of the room is always my first preference. However, moving sub-woofers or listening positions isn't always possible. Equally some rooms have dimensions that are very challenging (I don't know you but you clearly know what you are on about so you know what I am talking about).

    In the early days of digital correction I avoided it like the plague as the results were less than impressive. I first heard the results of an Audyssey EQ Pro in a grotty room in a hotel near Reading and it was astounding.

    I have a very "difficult" room here at home which doubles as my showroom. The dimensions are not what anyone would want. Adding an Audyssey EQ Pro brought a huge improvement to the sound quality.

    Lots of my clients have bought amps that have room correction in-built. The cheaper amps / receivers appear to work much better with the room correction devices switched off provided that the room is set up well. The more expensive units have better room correction and even with a physically well configured room there can be benefits from using their room correction modes (often with substantial manual intervention on the automatic routines).

    Digital correction appears to worry some. It worried me with the early versions.

    Client driven? - yes if they have bought an amp / receiver and I have to advise turning it all off if it doesn't work. In many cases my solution is optimising the physical layout then letting the electronics do their stuff - I have the test equipment to prove whether it is doing good or not.

    Budget driven? - no. Physical corrections are usually far cheaper.

    Personal preference? - No. A room of the right dimensions with the right materials probably won't need the help of digital correction.
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  27. Capoerista

    Capoerista Member

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    Craig,

    Thanks a lot! That's the answer I was looking for.

    I installed the REW program and getting acquainted with its basic features went quite smoothly. I used the sine wave generator to test the frequency range of my sub and found a very unpleasant resonance at 38-42 Hz, all done by simple hearing.

    Now I'm struggling to somehow cancel these frequencies out. I tried to find a good equaliser, but none has the resolution I need. So what did you mean by a good equaliser plug-in? Can you please name any specifics?

    Right now I'm stuck with a convolver plug-in from Convolver — a convolution plug-in

    I'm not at all sure this is the right tool to use, but its description says it can be used for bass management, peak reduction and equalisation, which is just what I need.

    Then I tried to use REW and convolver together, so I added an EQ filter in REW, of the type PK for peak, frequency 40, gain -30, Q=10 (4,0 Hz). I exported filters impulse response as WAV and loaded in convolver. As I feared, it doesn't seem to reduce resonance, so please tell me if I just screwed the parameters or let me know where I can find a proper equaliser. Also, I have no idea what the Q parameter really adjusts and can only suppose it is for the 'width' of the frequency range. So is the 4 Hz, as in my example, the correct setting, or should it be something else?

    Isn't there a plug-in where you simply input the frequency range to be cleared and that't it?
  28. craigd

    craigd Member

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    Not off the top of my head - I was thinking you could just download a very simple EQ plugin or use the built in one in WMP (View > Enhancements > Graphic Equalizer). By good I meant a higher resolution and/or parametric EQ plugin - parametric EQ allows you to adjust the centre frequency, bandwidth (Q value) and gain of the cut.

    It is an excellent tool if you know what you are doing with it. You need to create FIR filters to use with convolver. I used a piece of software called Acourate to do it before but its expensive - I only had the trial version I think. Duff Room Correction will also do it. These methods can correct the whole frequency range but require accurate measuring equipment.

    I have never tried to do this but I guess the format of the WAV isn't accepted by the convolver. It is a very complex task, especially if you have little understanding of equalisation. room correction and the tools involved. Try just with the built in equaliser to see if you can improve things first - if you have success heere, look in to buying a Radio Shack SPL meter and follow some of the online REW tutorials using a parametric EQ plugin instead of the Behringer Feedback Destroyer that a lot of people use.
  29. Capoerista

    Capoerista Member

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    The I reason I resorted to convolver is it accepts impulse response sound files as WAVs, as stated in its documentation, and REW has the option to export FIR as WAV, which to me happened to be a blessing coincidence.

    But never mind. Again by coincidence, I went through the settings of my already installed programs and found VideoLAN and ffdshow to have the options I need. In VideoLAN there is a 3 band parametric equaliser, and ffdshow has a FIR filter option, which is more universal as it should apply to sound streams played in all programs (unlike VideoLAN).

    So thanks again for your help, now I hope I will be able to get somewhere with these tools.
  30. craigd

    craigd Member

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    There is more to it than it just being a WAV - it needs to be the correct sample rate and there may be other constraints too.

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