Optimum room dimensions for reducing modes/standing waves/etc...

Discussion in 'Home Theater Projects' started by Tab Nichols, Jul 8, 2003.

  1. Tab Nichols

    Tab Nichols Stunt Coordinator

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    Good evening...

    I am in the process of building my house, so I have a ton of flexibilty in the dimensions of my home theater room right now.

    What is the perfect ratio for the rectangular room I should build to minimize the amount of problems I will have from standing waves, peaks and nulls, etc, etc...

    My proposed room (to the wife) is about 15x24 feet.
    I hope to do a front projection set up with a wet bar in the back...

    Any thoughts?
     
  2. Rick_Brown

    Rick_Brown Second Unit

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    Do a search in this forum. This has been discussed in detail many times.
     
  3. Jon Gum

    Jon Gum Stunt Coordinator

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    Tab -

    Send me a PM with your e-mail address. Tonight when I get home, I will send you a calculator that I ran into that helps calculate peaks and nulls at various frequencies based on room size and seating position. This is a tool and definately not an exact science, but at least it will give you a starting point and give you something to think about.
     
  4. scott>sau

    scott>sau Stunt Coordinator

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    The right room is the right size, right shape and has the right acoustics.
    Room size: (1000-6000 CF/cubic feet). You determine CF by multiplying LxWxH.
    Room shape: rectangular preferred. Dimensions should not be multiples of each other (8x16x20, 10x16x20, 8x14x28-are all bad!)
    Room acoustics could probably be covered in depth in another thread, but email me if you have specific questions.

    Standing waves: Multiple sub woofers placed asymmetrically to yield the smoothest response and cancel standing waves.

    Works cited: Russ Herschelmann, "HT, Essential Elements" (1995)
     
  5. BobAZ

    BobAZ Stunt Coordinator

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  6. Terry Montlick

    Terry Montlick Stunt Coordinator

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    Hello Tab,

    Optimal room dimensions have been the subject of study for several decades. It is a surprisingly nasty problem. Calculating room modes from room geometry may predict potential problems, but detailed interpretation remains elusive.

    The newest and most commonly excepted formula for room dimensions was proposed in 1996 by Robert Walker of the BBC. It's been adopted as a standard by both the International Electrotechnical Commission and the European Broadcasting Union. It is simply this:

    1.1w/h
     
  7. Terry Montlick

    Terry Montlick Stunt Coordinator

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    Here's the room dimensions calculator I promised.

    It is an Excel spreadsheet that you can use for free. You just type in the proposed room height, length, and width, and it tells you how these need to be modified to conform to Robert Walker's formula.

    Just go to:
    www.componentacoustics.com
    and click on the link marked "New! Room Dimensions Calculator"

    Regards,
    Terry
     
  8. Harley

    Harley Stunt Coordinator

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    Terry

    I can't get your calculator to open it directs me to a PDF file with nothing there.

    Have you ever seen these formulas?

    This one I believe is from Lucas(THX):

    1 X 1.78 x 2.33

    This one was posted by anonymous:

    1 x 1.6 x 2.6

    Harley
     
  9. Terry Montlick

    Terry Montlick Stunt Coordinator

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    Since I decided to write this using Microsoft Excel, you have to have Excel on your computer for this to work. Sorry!

    The neat thing about Walker's work on room dimensions is that he doesn't prescribe specific ratios, but gives only relative ranges. He came up with these ranged by analyzing rooms using a simple "quality" index, which he derives from the room mode spacing below 120 Hz.

    WARNING: BORING TECHNICAL STUFF TO FOLLOW. [​IMG]
    I did computer simulations of room acoustics using several of the most popular room ratios. These used a reasonably accurate model I developed, requiring numerical solution of the wave equation. I was surprised to find greatly different results depending upon how much absorption I put in the simulated rooms. The absorption affected the bandwidths of the modes, and made adjacent modes combine in unpredictable ways, depending on their phases. So unfortunately, even the recommended ratios are no absolute guarantee.

    In this context, Walker's simple rules (implemented in my calculator) seem especially sensible to me. So enjoy the Room Dimensions Calculator!

    Regards,
    Terry
     

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