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room cancellation modes / standing waves in new practice room

Discussion in 'Amps and Cabs [BG]' started by OldogNewTrick, Aug 31, 2008.

  1. OldogNewTrick


    Dec 28, 2004
    Germany, EU
    hi all, please don't bash me... I know I should know all this.. :bag:

    I also know that there have been some threads about such questions in the past, but just help me out here :help:

    I've moved to a new house, where I've got finally my own practice/music room:

    4,30m long x 3,25m wide x 2,42 m high.

    I've got lightly furnished walls, some shelves writing desk and the usual stuff in there, but no special acoustic dampening measures.

    What would be the standing wave frequency in there and how far should I place the cab from the wall to avoid booming.
    I've got a decent hifi in there to act as band substitute.

    Any tips on what to put on the walls ?
    The floor is carpeted btw., walls are hollow core bricks with gypsum board cladding, which is prone to vibration.

    Any recommendations ?
    Thanks guys.
  2. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    I don't know the math (yet) but IME the best low-tech way to deal with these things is to put bookshelves all around the walls and fill them with books and magazines; then just experiment with the speaker cab placement.
  3. SpankyPants

    SpankyPants That's Mr. SpankyPants to you.

    Aug 24, 2006
    Brooklyn, NY
    Build a smaller room inside of that room and place your amp in the center.
  4. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
  5. SERPENT865


    Jan 1, 2007
    Wichita , KS
  6. will33


    May 22, 2006
    Here's a link to the chart:


    You're going to have to convert all this to metric and then do the math. I think you want the source to be less than 1/4 wavelength or more than 1 wave length apart. This distance changes with frequency. There are real engineers on here who can expand on this. You'd have to figure out what the problem frequencies are and then figure out where you want to be in relation to the boundries, or just move your rig around a few different spots and find one that sounds best.
  7. will33


    May 22, 2006
  8. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    That type treatment does very little below 500 Hz, so it suppresses midrange, not bass. The usual room treatment for excessive bass is bass traps.
  9. thefruitfarmer


    Feb 25, 2006
    Kent UK
    Don't buy bass traps - you can build your own for a fraction of the cost.

    Have a look at this forum as a starting point.
  10. OldogNewTrick


    Dec 28, 2004
    Germany, EU
    thanks Bill. I lost the link to mcsquared's room mode calculator...

  11. OldogNewTrick


    Dec 28, 2004
    Germany, EU
    arrrgh, the old conundrum...

    data doesn't equal information which doesn't equal knowledge :mad: :oops:

    the basic table gives room modes at even multiples
    in length at 40 - 80 - 160 -320
    in width at 53 - 106 - 212 - 424
    in height at 70 - 140 - 280 - 560

    the room mode calculator provides more information:
    axial modes at odd multiples
    57,33 - 172 - 286 - 401 - 516
    6,88 - 20,6 - 34,4 - 48 - 62
    4,1 - 12,3 - 20,5 - 29 - 37
    114,67 - 229 - 344 - 458
    13,7 - ....
    8,2 - ....

    tangential room modes at half the energy (-3dB) at odd multiples
    57,74 - 173 - 288 - 404
    57,48 ....
    8 ...
    115,5 ...
    115 ...
    16 ...

    and not to forget, the oblique modes at -6dB
    at 58 - 116 - 174 - 232 - 289 - 347 - 405 ...

    so what frequency do I choose now to find the cancellation distance from the boundaries ? presumably to each of the walls ???

    I've got a headache :confused: :crying:
  12. thefruitfarmer


    Feb 25, 2006
    Kent UK
    You don't need to get hung up on the figures too much...

    ...their accuracy will depend on how accurately you measured the room any way.

    Assuming the maths is done right you will be able to hear the artifacts of the room. If the first mode is at 40Htz that will be the bottom E string on the bass. You can play the note and walk around the room. It should sound louder in the corners and quieter in the centre of the room - it may be hard to hear initially but once you can hear it you won't stop noticing it.

    Acoustics is a complicated subject but you only need a basic understanding to treat a room.

    So, why I am saying you don't need to worry about the figures too much?

    If you take the option of building a tuned panel trap or a helmholtz trap then you will have to do calculations, testing and adjustments of the finished item. This requires a knowledge and application of maths and physics. These absorb a specific frequency of sound.

    What most people do is build "broadband absorbtion" panels or "superchunks", which absorb across a wide range of frequencies. These devices are slabs of mineral wool mounted in frames and are most efficient across the corners of a room, where the sound energy is more focussed.

    I suggest you do a bit of research, look at peoples' build diaries and concerntrate on the practical stuff rather than getting too hung up on the physics. You can take a "suck it and see" approach with the acoustic treatment in that you will be able to hear the problem then you just keep adding mineral wool panels until the bass in the room sounds clear and even.
  13. thefruitfarmer


    Feb 25, 2006
    Kent UK
    To honest, you would probably be better off asking about this in a forum that specialises in acoustic treatment, studio builds, that kind of thing. You need to chat to people who have done what you intend to do and learn as far as you can from their mistakes.

    This article is a good starting point.

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