Room dimensions for best acoustics

[fred1942]

My family is growing and I need some extra space for us to recreate. So, I am in the initial stage of planning a room addition. I am thinking about 24 x 42 with a 10 or 12 foot ceiling. One end of it will be a home theater with the sitting area about 12 feet from the wall where a large screen tv will go. I am considering Ascend speakers. Is there a ratio for length and width for best acoustics? Room will be carpeted with some acoustic panels. Any thoughts?

 

[STRONGBADF1]

I assume this is accurate...

RealTraps - ModeCalc

 

[FirstReflection]

There are a couple of ways to come at room acoustics:

1) you can go for predictable reflections, room modes and echoes so that you can have a pretty good idea beforehand as to what you will need to address and where your trouble spots will be, or...

2) you can try to eliminate as many reflections, room modes and echoes as possible.

For option 1) you'll want to build a rectangular room. You will want to make sure that none of the dimensions (length, width or height) is identical or an even multiple. A cube is the worst shape possible. And a room that is, say, 10 feet wide and 20 feet long will also have a lot of issues since the length is an even multiple or the width in that case.

If you'd like highly predictable room modes and what is generally considered a "good" rectangular room acoustically, you can use the "golden ratio" of 1.618:1. Make the width of the room 1.618x the height, and make the length 1.618x the width. The golden ratio just so happens to produce very few instances where one dimension's standing waves intersect with another dimensions. In other words, a standing wave that results from sound waves bouncing between the front and back wall won't be at the same frequency as the standing waves that result from sound waves bouncing between the two side walls, or from the standing waves bouncing between the ceiling and floor. The opposite end of the spectrum is a cube, where the standing waves will all be at the same frequency, creating massive nulls and peaks that basically cannot be overcome no matter what you do.

For option 2), you need a much more complex build because you would want to create a room that does not have any parallel walls. An example would be something like the dubbing stage shown here . A room such as that will also have a ceiling that is, say, 10 feet at the front of the room, but 12 or 14 feet at the back of the room, with the ceiling slanting upwards from front to back so that it is not parallel with the floor.

Such a room will also be acoustically treated with absorption, bass traps and diffusion. All of that will work to greatly reduce reflections, avoid room modes and eliminate echoes.

 

[cpp]

As a FYI a few good sites for acoustics

Acoustics 101...Practical guidelines for building a sound studio, listening room, home theater room, and any other sound control room project.

Acoustics Forum • Index page

 

[GranteedEV]

My family is growing and I need some extra space for us to recreate. So, I am in the initial stage of planning a room addition. I am thinking about 24 x 42 with a 10 or 12 foot ceiling. One end of it will be a home theater with the sitting area about 12 feet from the wall where a large screen tv will go. I am considering Ascend speakers. Is there a ratio for length and width for best acoustics? Room will be carpeted with some acoustic panels. Any thoughts?

That room is really big for a home theater; you might not get any room gain. Personally I'd shring the 42 foot dimension by a good amount, maybe down to 30 feet.

The 24 inch width dimension is good. Assuming your left speaker and right speaker are about 10 feet apart, that would leave about 6 feet on either side to delay early reflections.

Taller ceilings might be nice though - maybe 16 feet instead of 12, with a drop-down ceiling diffusor hanging from it.

As far as room modes in the bass are concerned, it's rather difficult to NOT run into them. Your best bet is to excite them uniformly with multiple subs and bass traps, rather than expecting to avoid exciting them. That said a moderately rectangular, symmetrical room is a good idea.

Beyond that you might wanna read this:

http://www.gedlee.com/Home_theatre.htm

 

[fred1942]

That room is really big for a home theater; you might not get any room gain. Personally I'd shring the 42 foot dimension by a good amount, maybe down to 30 feet.

The 24 inch width dimension is good. Assuming your left speaker and right speaker are about 10 feet apart, that would leave about 6 feet on either side to delay early reflections.

Taller ceilings might be nice though - maybe 16 feet instead of 12, with a drop-down ceiling diffusor hanging from it.

As far as room modes in the bass are concerned, it's rather difficult to NOT run into them. Your best bet is to excite them uniformly with multiple subs and bass traps, rather than expecting to avoid exciting them. That said a moderately rectangular, symmetrical room is a good idea.

Beyond that you might wanna read this:

Home Theater[/QUOTE

12 feet of length for tv, couches, speakers, etc., 12 feet length for pool table, 4 feet for bar and stools, 3 feet for cabinets, 5 feet for closet space and 6 feet for walking space. I like your idea for a taller ceiling, maybe cathedral.

 

[fred1942]

There are a couple of ways to come at room acoustics:

1) you can go for predictable reflections, room modes and echoes so that you can have a pretty good idea beforehand as to what you will need to address and where your trouble spots will be, or...

2) you can try to eliminate as many reflections, room modes and echoes as possible.

For option 1) you'll want to build a rectangular room. You will want to make sure that none of the dimensions (length, width or height) is identical or an even multiple. A cube is the worst shape possible. And a room that is, say, 10 feet wide and 20 feet long will also have a lot of issues since the length is an even multiple or the width in that case.

If you'd like highly predictable room modes and what is generally considered a "good" rectangular room acoustically, you can use the "golden ratio" of 1.618:1. Make the width of the room 1.618x the height, and make the length 1.618x the width. The golden ratio just so happens to produce very few instances where one dimension's standing waves intersect with another dimensions. In other words, a standing wave that results from sound waves bouncing between the front and back wall won't be at the same frequency as the standing waves that result from sound waves bouncing between the two side walls, or from the standing waves bouncing between the ceiling and floor. The opposite end of the spectrum is a cube, where the standing waves will all be at the same frequency, creating massive nulls and peaks that basically cannot be overcome no matter what you do.

For option 2), you need a much more complex build because you would want to create a room that does not have any parallel walls. An example would be something like the dubbing stage shown here . A room such as that will also have a ceiling that is, say, 10 feet at the front of the room, but 12 or 14 feet at the back of the room, with the ceiling slanting upwards from front to back so that it is not parallel with the floor.

Such a room will also be acoustically treated with absorption, bass traps and diffusion. All of that will work to greatly reduce reflections, avoid room modes and eliminate echoes.

Some great ideas. Thanks.