Comments on: The 3:1 Rule

By: G. E. Marrs

G. E. Marrs — Fri, 04 Dec 2009 01:02:00 +0000

For some reason, when I read the definition, it sounded like it said that if the first mic is 3ft from a speaker, than the second mic should be 6 feet away from the speaker (regardless of any distance away from the mic). Then I continued reading and it cleared up, especially from the diagram.

I’ll be sure to keep this in mind. Good future reference.

By: Joe

Joe — Wed, 25 Nov 2009 17:05:42 +0000

another 3:1 rule I just learned was keeping the microphone a good distance from a source that has a lot of movement. While recording drums, the drummer and singer insisted a microphone on the splash. Whenever we listened to it we kept hearing a long whirling gong song on the tail end of the initial hit. (almost like Time Warp, but with sound) My fellow engineering buddy told me we were too close because the splash had a lot of movement available on the hardware it was sitting on. The measurement of the lowest point to the highest point the splash would move (hardest the drummer would hit it) was about 4 inches. Using the 3:1 rule meant that in order to get rid of that weird sound we would have to have the mic around 12 inches away. Having a splash mic was useless, since we had overheads going. It’s not a black and white rule (use your ears rule) and it depends on the how much movement the transient has when played or struck too.

By: Joe Gilder

Joe Gilder — Wed, 25 Nov 2009 15:09:31 +0000

Thanks Det. And welcome!

By: not_a_monkey

not_a_monkey — Wed, 25 Nov 2009 14:37:39 +0000

As a rule of thumb, 3:1 works quite nicely.
In your example with multiple mics in front of a choir all mics face more or less the same direction, and evidently there is some kind of stage involved. In other words, there _is_ more space available. No harm in using a 4:1 or higher ratio, but in the result you’ll have to take care to get a proper stereoscopic result of the different sections provided with a mic.
However, in a comparably small room, say, a broadcasting studio, you may have mics placed in different directions to record/broadcast an interview situation. There’s no room for a higher ratio, and if there’s more room the intimacy of the interview will be lost. But a smaller ratio like 2:1 may cause severe undesired comb filter effects.

By: det

det — Wed, 25 Nov 2009 14:18:34 +0000

i’ve just met your blog, and i must say that is awesome!

“do what sounds best” should be the motto of every sound technician out there, regardless of what the “book” says!