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In Reply to: RE: Looking for recommendation on ceiling height posted by jim94025 on October 12, 2009 at 10:12:55
Optimum ratios were initially developed for reverberation rooms, where measurements of sound fields of machines etc. were to be made. Machines produce noise, i.e. the whole audible frequency spectrum, or major arts thereof, simultaneously and all the time. For measuring the sound field microphones are placed all around the machine. Since the whole spectrum is constantly emitted, all of the possible room modes are excited all the time. In order to obtain useful readings from all microphones the mode frequencies had to be spaced evenly on the frequency scale. Somehow this approach had found its way into home audio.
However, what are you doing by selecting "optimum room dimension ratios" ?
You are spacing all of the possible room modes according to some particular criterion on the frequeny scale, the emphasis being on ALL.
In order to take full advantage of the optimization you'd have to excite all of the room modes and what is more, you'd also have to perceive all of those excited modes. If you excite only some of the modes and you then perceive only some of these excited modes, why use a criterion that optimizes ALL modes?
The only place where you are able to excite AND perceive all modes are room corners, which means that loudspeakers and listening position have to be right there, in a corner. You'd further have to take care that you excite all modes at any given moment, which is simply not possible when playing normal music.
Since all of those optimization methods are, inherently, designed to obtain optimum conditions for room corners only, my advice is to just forget about this optimum room dimension issue. If possible, avoid ratios where one dimension is a multiple of another, but even in this case, the result is not necessarily worse:
Fazenda et al., “Perception of modal distribution metrics in critical listening spaces - Dependence on room aspect ratios”, J. of Audio Engineering Society 2005, p.1128
In the case of a cathedral ceiling you are leaving the area of rectangular rooms anyway since there won't be any axial and tangential vertical modes, and the pressure lines of the horizontal modes are probably no longer parallel to the room boundaries but curved instead.
Klaus
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