Placing Loudspeakers Correctly

March 24, 2006 12:12 PM

What are the physics concepts and equations behind loudspeaker placement in a simple rectangular room?

I understand nodes and antinodes on a very low level. Is the point of placement to get rid of most nodes and antinodes or create them in places where you're likely to be sitting and listening to music? How do I go about using measurements of the room and the placement of loudspeakers to get sound to fill the entire room somewhat uniformly?

posted by authenticgeek to Science & Nature (6 answers total)

Nodes and antinodes aren't really useful to think about unless you know the frequencies that the speaker will be outputting. Where interference occurs is a function of the wavelength, which is 1/frequency.

You should mostly be concerned about echos and absorption.
posted by aubilenon at 1:09 PM on March 24, 2006

You could try the 3:1 rule for microphone placement. Yeah, I know you're placing speakers, not microphones, but the rule should work in reverse.
posted by fvox13 at 1:30 PM on March 24, 2006

The general rule of thumb for placing a pair of loudspeakers is to put the speakers at the corners of an equilateral triangle with the listener at the third corner (I'm assuming you're placing a single pair of speakers and not a surround sound setup).

Here is a writeup that gives a simple treatment of some of the physics involved. Googling for "speaker placement physics" gets you a bunch more information.
posted by pombe at 1:58 PM on March 24, 2006

Stereo? 5.1? Here's a Wendy Carlos article on surround sound.
posted by glibhamdreck at 2:28 PM on March 24, 2006

I like the Cardas method. The main idea in any set-up is to reduce room nodes and to get a good sound stage. A RadioShack sound meter and a speaker set-up CD with tones at different frequencies can help dial in the room nodes thing if you are having trouble. Mostly, trust your own ears.
posted by caddis at 2:58 PM on March 24, 2006

Once you get the placement dialed in to something you like make some marks somehow to remember it in case they get moved. Some people like to couple the speakers to the floor with spikes which diminishes the possibility that they will get moved. It sort of depends on who you live with and who cleans the place. It's funny, but even a half an inch (especially in rotation) can make a difference depending upon your speakers and room. The Stereophile Test CD 1 (available here) has test tones if you want to use the sound pressure level meter to see how flat your in-room response is as you adjust the speakers. If you do this, put the meter on a tripod or something at your listening location. Don't hold it in your hand as it is somewhat directional and you will have it oriented differently for every reading that way. The idea is to take a similar reading at each frequency.
posted by caddis at 4:46 PM on March 24, 2006