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RE: Room Dimensions

Posted by David Aiken (A) on May 10, 2011 at 17:09:59

In Reply to: Room Dimensions posted by Bardo on May 10, 2011 at 10:43:34:

Room dimensions are less important than you think.

Certainly the frequency of room modes is determined by the dimensions, and having 2 dimensions which are equal or exact multiples of each other will result in some modes being generated along 2 axes, exacerbating those modes, at least in theory. Cube shaped rooms are even worse with all 3 dimensions the same resulting in maximum axial mode reinforcement.

BUT that's really only a problem when modes are being maximally excited. How strong a mode is excited depends on where the speaker is placed, and also on where you sit because you can be sitting anywhere from in the middle of a null to the middle of a peak depending on where in the room you place your seat. In practice you won't excite all modes maximally unless you place the speakers in corners and then you won't hear it at its worst unless you sit in another corner. In practice things usually aren't as bad as they look on paper and if you have a fair amount of leeway on where you place the speakers and listening position you can make most rooms work reasonably well regardless of dimensions.

In your case with a 7.1 setup the listening position is going to be rather constrained because it has to be in the centre of the "circle" of speakers and it also has to be far enough from each speaker for the sound from that speaker's drivers to integrate fully.

Given the need for space for the speakers, I'd go for as large a room as possible. Take a look at your speaker's specs and the recommended listening distance (try emailing the manufacturer and asking if that figure isn't provided in their info). Then I'd start with screen placement, work out where the seating has to be for good visual presentation, work out the size of the listening area depending on how many seats you're using, then work out where the speakers will need to go based on the recommended listening distance. Then look at the specs for placement recommendations in relation to distance from walls, mark that out and you've got a reasonable set of starting figures for room size. Adjust dimensions slightly if you get 2 dimensions which are related by a multiple, perhaps make it a little bit bigger if you're planning on upgrading to bigger speakers at some point in the future, and you've got the size for your room.



David Aiken

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