Need to make a room long enough for the wave to commense??

audioeric · Post by **audioeric** » Mon Sep 08, 2003 8:11 am

Hi, we're getting ready to build a new control room, and someone had told me that the control room needs to be big enough so that the lowest wave can go from zero to compressed to rarefacted and back.. so, basically they were saying that our room needed to be like 22 feet long, and that sounds could only be produced if they had enough room to fully cycle..

Is this fact or fiction?

thanks for the help!!

eric

barefoot · Post by **barefoot** » Wed Sep 10, 2003 4:21 am

This post is by Ethan Winter
(moved from another thread)

Eric,

Replying to your original post gives an error, so I had to create a new thread.

> someone had told me that the control room needs to be big enough so that the lowest wave can go from zero to compressed to rarefacted and back <

The short answer is it's pure fiction.

The longer answer is it's helpful if a room has at least one dimension long enough to provide modal support for the lowest frequency you hope to reproduce. The good news is that bass trapping can make even fairly small rooms accurate enough to mix in with confidence. Also, if the walls are made of light material - 3/8 inch drywall instead of thicker drywall or brick, etc. - the very low frequencies will pass right through to the outside. The root problem with all rooms is low frequency reflections off the walls, floor, and ceiling. So reducing the low frequency reflections always helps solve the low frequency problems.

Have a look at my Acoustics FAQ, tenth in the list here:

www.ethanwiner.com/articles.html

Then see the sidebar "Big waves, small rooms" for more on this, as well as the sidebar that describes the ModeCalc program.

--Ethan

audioeric · Post by **audioeric** » Wed Sep 10, 2003 6:03 am

Thanks both to Ethan Winter and Barefoot.. You guys make this forum a great one!!

I had read your FAQ a while ago, when I first started doing research for our control room expansion/studio makeover.. hmm.. studio makeover.. sounds like one of those makeover shoes on TLC.. maybe we can all get Trading Spaces to do a HI FI show.. And instead of just designers, have designers for aesthetics and look, and people like John and Ethan and so forth for acoustical design.. hmmmmm..

:p Anyway, back to the point, your FAQ was a good read.. a long read.. but a good one..

The reason I asked the question is that the other engineer at my studio was adament on having the room be very long so that it could encompass the whole wave.. And I agree that its better to have a longer room, for the reasons you mentioned, his theory behind it seemed a bit skewed..

anyway.. thanks again fellas..

eric

Post by **John Sayers** » Wed Sep 10, 2003 7:16 am

having the room be very long so that it could encompass the whole wave

surely the longest dimension is from corner to corner??
also - I can hear low frequencies in headphones

;) now that's a really small room

cheers
john

barefoot · Post by **barefoot** » Wed Sep 10, 2003 8:19 am

In fact, headphones illustrate a very important fact relating to the size of a room and its response characteristics. Rather than having limited bass response, small rooms significantly enhance the bass. Have you noticed that when you take off headphones and listen to them they have almost no bass output? Or, when you roll down the windows of your car a lot of the bass disappears?

This doesn't have to do with standing waves. The wavelengths we are talking about are far too large compared to the room dimensions to create standing waves. This has to do with the fact that as wavelength increases the sound reflecting from the walls becomes more and more in phase with the direct sound. So, the reflections produce more and more constructive rather than destructive interference as wavelength increases.

The effect is called "bass lift" and it makes it very difficult to get a flat bass response in small rooms - i.e. there is too much bass rather the not enough.

Thomas

audioeric · Post by **audioeric** » Wed Sep 10, 2003 1:15 pm

Thanks guys.. Yeah, the whole thing just really didn't jive in my head.. The same person who said this only likes to mix from headphones.. Which is even funnier.. He wants the room to be large enough to encompass the wave, but he mixes primarily on headphones.. Yeah, it's a bit of an interesting situation.. Thanks again

eric