Systemic Development > Psycho-Acoustics

need help designing an audio/HT room

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Nick B:
My wife and I have decided to build a new house and many issues have been resolved. The remaining stumbling block is the shape of the audio/video room. It is being located next to a courtyard and we have a shape that is somewhat trapezoid. Overall, I'm trying to get a 12-14' X 16-18' size. I would like 5 channel only, so 2 side wall speakers (of reasonably good quality) would be fine for video. The problem is that one of the side walls would be at an angle rather than directly facing the other. If the design problem can't be fixed, then would ceiling built ins sound similar to a side wall installation? Any comments about this, room size or any other recommendations would be appreciated.

richidoo:
Congrats Nick! Good luck in your building project. It is a process with a capital P, but always worth the effort when you get a nice new house at the end.

The non parallel sides are great for acoustics, same reason a lot of speakers have non parallel side walls, to minimize internal resonance due to reflections. For stereo listening you want it more lively than HT which can be more dead, so it's better to have the angles between the side walls and the front wall be equal so the stereo soundstage is balanced especially with a smaller front wall. But instead of one slanted front wall, you could make it two smaller, slightly angled (almost inline) walls, as long as everything is symmetrical down the centerline. One small wall built from the center of the front wall to a point on the side wall which comes off the acute angle to the front wall, in order to make the front of the room symmetrical. That would be a great stereo room. The rear wall's angle is not as important and can be made symmetrical or not, and can be treated with absorbtion to minimize reflections off the back. For stereo listening you could put diffusion on the back wall if you like a more lively sound. So non parallel side walls is ideal for stereo listening if you can keep it symmetrical down the center of stereo line. Great for HT too, of course.
Rich

Nick B:
Hi, Rich.                                                                     Your answer surprised me. I assumed an irregular shape would be a problem. Right now, it appears that the front, rear and left side (facing forward) walls will all be perfectly square. The right wall might be wider at the top and then angle narrower towards the rear. Other than curtains and carpeting, I've never used any materials for room treatment. I do have a friend who did a seven channel setup with 4 in wall speakers, so I'll check with him also. He might have ACI as I recall. Thanks for your input
Nick

bpape:
Can you post a sketch of the available space?  

Odd shaped rooms can be a blessing and/or a curse.  You'll minimize standing waves in the non-parallel dimensions but you'll also shift the bounces to all come from one side - throwing the surround image off if you don't kill the reflections somewhat.  Also, odd shaped rooms are much harder to predict in terms of optimal seating distances, why certain frequency response anomolies exist, etc.

Bryan

richidoo:
Hi Nick,
Something like this is what I was thinking about. You still have to make the walls symmetrical to the stereo center line and can do that by adding one or two small walls. The rear wall isn't as critical (IMO) to be symmetrical to the center line, especially in HT where you will probably deaden it with absorbtion anyway. But front wall is absolutely critical to the stereo presentation and the side walls are almost as important, but they get some treatment anyway so you can be a little off. If you're gonna deaden the whole thing down to HT standards (<.3sec -60dB reverb) then a slight non parallel doesn't even matter. On your second post you made it sound as if the side walls are not too far off parallel anyway, so you might not need any big changes.

I like a more lively room for stereo listening, so reflected sound should come from symmetrically angled walls to maintain the best possible stereo imaging. My downstairs room is huge an unsymmetrical and imaging is fine. If the room is big enough it is not a big deal. But when it is small your ears are closer to the walls and can sense the angles effect. It is kinda pickin nits though unless it is like 30 degrees off or seomthing wild.

I was reading this cool article about room setup yesterday by Cardas, proponent of tapered walls (& ceiling!) For kicks I tried setting up my speakers according to the Cardas Golden ratio yesterday. There was maybe a slight improvement, bass was better, but nothing earth shaking. My upstairs room is too small for this because it puts me only 5' from the speakers. I think there is much more science available above and beyond the superstition of golden ratio when it comes to acoustics. But the tapering walls makes sense  to me if done right, of course. Non parallel walls shouldn't be too steep.

It would cool to see a pic of what you have to work with.  :D

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