Just saw this 18 minute video by John Dahl from THX discussing room modes (or peaks) and various ways to deal with them, including the use of multiple subwoofers, room treatments, and certain isolation and bass-trapping products. Its one of the better presentations on this topic.

As it says in the executive summary:


"This video gives a great overview of what it takes to tame the frequencies in your room below 200Hz - where the room really makes itself known. Taming bass response in a room is important as it can really make or break a sound system.

Additionally, with proper calculations, you can model how a room will interact with bass frequencies and better position your seating positions to . Among suggestions, John offers 5 tips to getting better control over your bass.


Choose a room with dimensions that are 5% different from each other

Don't position any seats in areas which have peaks or dips

Place subwoofers in such a way as to better diffract energy in the room

Use mechanical bass treatments (must be an active or resonant device in order to work)

The LAST thing you can do is equalize the room

This is a video every bass-head should watch and learn from. Everyone can do at least some of these steps in order to get better bass response and smooth out the bass so that you achieve better sound and a much more pleasing home theater experience."




Anyway I highly recommend everyone watch this well done educational video.

http://www.audioholics.com/news/trade-show-coverage/videos/thx-managing-bass-modes

Thanks John, love it...

Cool!

Great avatar Nick.

Thanks John!

I'm reminded of Steve Martin's old bit:

You too ... can be a MILLIONAIRE, and NEVER pay TAXES!
First: get a million dollars



Patient: Doctor, it hurts when I do this.
Doctor: Don't do that!

Yes. I thought that was a silly way to say that as your room approaches square dimensions you are going to have more issues. I suppose his point is that if given the choice choose the more rectangular room.

I've always heard that ideally the best room is where the dimensions don't easily divide into each other. For ex, a 24 x 12 x 8 would not be ideal, compared to a 19 x 12 x 8.

Also, the worst place to sit is 50% or center of the room. The first choice would be 38% from the front wall, and if this is not possibe 38% from the back wall.

Its interesting how that ratio keeps popping up. One rule of thumb that has stuck to me is that for rooms with 8' ceilings the length should be 1.39 times the width. Aurelex goes further and suggests the ideal acoustical space would be roughly 21 x 15 x 8.

http://www.acoustics101.com/common/table5_1.jpg

http://www.acoustics101.com/room_dimensions.asp

One of the big challenge is also that, very often, rooms are irregular and can have portions with good and some with bad dimentions. It happened to me once and it was quite a challenge to get both highs and lows to be well dispersed (i.e. painting of left wall, bare on right, furniture in some corners...).

I know what you mean. I have (had) a challenging HT room with 21x 19 x 8 dimensions which is far from ideal. It took months of experimenting with treatments, bass traps, placement of sofas and chairs, bookshelves to tame it.

I can sure relate about unusual room dimensions.

Really? Those dimensions would appear prima fascia to be good by virtue of not having any common factors.

Generally speaking as the room approaches square dimensions the problems mount...in my case huge room gain 25hz and below plus a couple of deep nodes. 19 x 21 isn't too far from 20 x 20.

I've read that the spl meters aren't accurate below, say, 45hz, so do you base that on measurements or on calculation?

RTA sweeps on a SMS display.