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

Tab Nichols · 07-08-2003, 09:15 PM

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?

Rick_Brown · 07-09-2003, 08:47 AM

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

Jon Gum · 07-09-2003, 01:56 PM

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.

scott>sau · 07-11-2003, 02:47 PM

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)

BobAZ · 07-11-2003, 05:21 PM

Some info I found at the Dolby site:
http://www.dolby.com/movies/m.in.0009.screensize.html

About 2/3 of the way down look for Acoustic Issues. They suggest a Golden Ratio of 1.0W X 1.55 D X 0.67 H

EDIT:
This may be the calculator (spreadsheet) Jon Gum referred to above:
http://www.guidetohometheater.com/shownews.cgi?388

My room is 16'W X 16'D X 8'H, the worst possible combination of dimensions.

**HTF Ads**

Terry Montlick · 07-12-2003, 06:35 PM

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 <= l/h <= 4.5w/h - 4

where l, w, and h are the room's length, width, and height, respectively.

The other rule is that no room dimension should be within 5% of any multiple of another room dimension.

If the math seems a little complicated, give me a few days. I think it's worth my writing a little Room Dimension Calculator Java applet, or maybe just an Excel spreadsheet which computes this. I'll post it on my company's web site for all to use, and put a note in this thread when it's ready.

- Terry

Terry Montlick · 07-14-2003, 11:05 AM

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

Harley · 07-14-2003, 12:54 PM

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

Terry Montlick · 07-14-2003, 05:25 PM

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.

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