My wife and I are considering the idea of having a room addition added to our house for a dedicated HT/two channel audio room. Is there an ideal length to width ratio for constructing an HT room? The maximum size I have to work with (outside measurements) is nineteen feet by twenty eight and a half feet. Also needing to be factored in is that I will need to have a false wall built two feet into the room along the rear short wall for component racks and media storage.
Also, is a flat ceiling (eight to nine feet) preferable to a cathedral ceiling in an HT room?

For purely box-shaped rooms, the best ratios that we know of follow the European Broadcasting Union (EBU)/Robert Walker formulas. These specify the safest ranges for relative length, width, and height. You can download a free Excel calculator for this from my web site. Many larger home theaters don't have sufficiently high ceilings, according to these criteria.

As for cathedral ceilings, these are not amenable to simple of room modal analysis. We use a Finite Element Model (FEM) to predict the modes of such rooms.

Regards,
Terry

http://www.hometheaterbuilder.com/issue/OptRmDim.htm

Perhaps this would help as well.

Is there an ideal length to width ratio for constructing an HT room?

Yes! :D

See this:

www.realtraps.com/modecalc.htm

The maximum size I have to work with (outside measurements) is nineteen feet by twenty eight and a half feet.

That's excellent, and you can definitely get a great sounding room in a space that large.

is a flat ceiling (eight to nine feet) preferable to a cathedral ceiling in an HT room?

When all else is equal, more height is preferred.

--Ethan

Thanks much, folks. It's greatly appreciated. That will help me begin to sort things out before I start talking to contractors.

Not to hijack my own thread, but I notice in a lot of pictures of HTs in this forum that soffits seem to be popular. I see that they offer some flexibility and ease in wiring, but do they offer any advantages in terms of acoustics? For example, if I were to line the insides of them with rigid fiberglass (Corning 703 or equivalent)?

Sure they can be used to make bass traps, but I think most people have them because of HVAC and similar issues.

I have no treatments on the soffits, since they are not that big.

Bull Island Theatre