Larger at one end than the other (no parallel surfaces). After that, Golden Dimensions are nice.

Acoustically speaking, there is no optimum shape (or size). If there were, all rooms would aim for that and we'd never have the huge variation we see. What's "optimum" depends directly on how much shell space you have available, and of course how much money you're willing to invest.

Now, there are plenty of guidelines. Minimum size for excellent results is generally quoted as 2500 cubic feet. Angled walls can be useful, but are not mandatory. Angling the walls does not help low frequencies much, though it can avoid flutter echo at mid and high frequencies.

Entire books have been written about this!

--Ethan

Quote:
Larger at one end than the other (no parallel surfaces). After that, Golden Dimensions are nice.

I seem to remember reading that those Golden Dimensions are able to distribute the standing wave modes more evenly across the frequency band than other ratios.

Quote:
I seem to remember reading that those Golden Dimensions are able to distribute the standing wave modes more evenly across the frequency band than other ratios.

There's no ideal ratio. Every shape is a compromise. If you'd like to play around with different dimensions to see how the modes relate, my Graphical Mode Calculator program makes this very easy.

--Ethan