Axiom Home Page Forums General Discussion Technical Questions theater room acoustics

Well, I am building my theater now. Using the "golden ratios" for room dimensions, I am going to build my room to be 7'-3" high, 11'-7 1/4" wide, and 16'-10 3/4" long. The screen will be 96"X56" and I am planning to simply have 2 rows of 4 theater seats in the room. From what I have read, the dimensions I have chosen are best (as a ratio of 1:1.6:2.33) for minimizing room peaks and nodes. In conjunction with the room size, I also will be using my trusty BFD to further smooth the room response.

These measures should really tame the bass response (hopefully to nearly ruler flat!), but what about the rest of the spectrum. I have read that room reflections are what generally muddy the sound of even the best systems, so how should I treat my walls. Do I leave the front wall solid, to allow reflections towards the seating, and then deaden the ceiling, side and rear walls to eliminate reflected sound? Do I leave a portion of the side walls un-deadened to allow some reflected sound?

I had Kind of leaned towards the first idea. If you are outside, the sound only comes from the one direction. Any sound that should sound reflected, such as bounced off a building or the lively reflections in a gymnasium, should (I would think), be re-created by the surround speakers and therefore I would want all walls deadened. Then I wonder if I can get good width and depth imaging if the front wall is deadened. I am leaning towards a stiff front wall that will reflect sound, much like an ampitheater. Perhaps the front wall, and the first four feet of the side walls and ceiling should be reflective. This would provide for a reflective depth, width, and height, without being so far out as to allow first reflections to be directed at the listening positions.

I have read that there should be a balance between reflective and absorptive materials, but I have never read any good "tried and true" facts. Anyone have any good actual designs that are proven to sound great?

I think minimizing all reflections should be your goal. Think of the room where they master the sound. I've seen one of these rooms at a company my uncle used to work for (POP Studios in Santa Monica). They pretty much deaden the entire room so any sound you get comes directly from the speakers. I remember seeing a lot of anechoic acoustic foam on the walls.

With that said, there's plenty of things you can do to your walls to deaden them. Acoustic foam is the least pleasing to the eye. A popular choice for home theaters is thick velvety "movie theater style" drapes along all the walls. Another option is thin acoustic panels, which resemble drywall wrapped in fabric.

if you use foam, be sure it's fire retardent; remember the rhode island nightclub fire.
dan

Thanks for the replies. To deaden the room I will use 2X4 furring over the masonry, filled with acoustic sound deadening fiberglass insulation (more dense fiberglass batts) with fabric over the top. I guess I was wondering if the front wall should be reflective to give a depth to the sound. Why is it that speakers should be placed a few feet from walls? I kind of thought that the front wall and maybe the first few feet of the side walls and ceiling should be reflective for this reason. You are saying that Imaging would be better in a dead room?

Here are some sources, there seems to be a lot on the subject on the web. http://www.echobusters.com/page1.html
http://www.eighthnerve.com
http://www.apluselectronics.com/acoustical_treatment.htm http://www.acousticroomsystems.com/7834_eprint.pdf

Personally i find anechoic rooms to be rather deafening.
How ironic eh?

Conventional wisdom is that the ideal room for 2-channel (front speakers only) listening is one with the "dead/live" configuration. Thus, the front half of the room is relatively dead -- especially the front and side walls near the speakers, reducing early-reflected sound coming from front, which will adversely affect sonic quality. On the other hand, the rear half of the room is more reflective. So, this is actually opposite from what you've described.

I agree with Peter that, for a multi-channel surround setup, the entire room should be relatively dead. But I don't think it should be much more dead than typical North American living rooms with carpeted floor, fabric-upholstered furniture, drywalls with some shelves, and some fabric window treatments.

I've actually been looking into acoustics for my room before I get my system. By all accounts most say that room accoustics are the most over looked and one of the most important parts of a system. The most expensive high end systems will sound like crap with bad accoustics... Most seem to recommend balancing between reflection and absorbtion and warn against making a room accoustically "dead"... It appears dampening the primary and secondary reflections have the greatest impact and that you typically want to absorb in the front of the room and diffract in the back of the room. Even though I'm just a novice I'd bet that all those folks complaining about Axiom speakers being "bright" are really describing their room accoustics, since not everyone seems to find this / agree. Properly adjust the room accoustics and violas the Axioms are no longer bright but totally neutral, and revealing. I think it makes sense for speakers with the qualities of the Axioms to easily appear bright with the wrong accoustics....?

Here's some sites for your purusal:

http://www.diyacoustics.com/files/pdf/platinum.pdf

http://www.angelfire.com/sports/RCcars/acoustic_panels.htm


http://www.asc-hifi.com/acoustic_basics.htm

http://www.audiorevolution.com/equip/cheaptreatments/

http://ic.net/~jtgale/diy2.htm

http://pat.home.mchsi.com/SAP.html

http://t-3.cc/users/audioworx/page3DIYpanels.html

http://www.rivesaudio.com/Links/Linkframes.html

http://www.realtraps.com/index.htm

http://www.audioholics.com/techtips/setup/RoomAcoustics-RivesAudio.html

http://www.audioperfectionist.com check out the Free Journal section either 1 or 2 has an HT article and how to set up speakers and accoustically treat a room. This guy makes a number of interesting points I'll likely ask advice / opinions on from the local forum experts
at some point.

Good Luck, El

great paragraph from the audioperfectionist.com

Would you accept medical advice from some anonymous @ on the internet? I guess some people do, but it?s risky business. And bad advice about audio is even more serious. Bad medical advice can only kill you. Bad audio advice can wreck the sound of your hi-fi and you?ll have to live with that!

What is everyones opinion on fabric-upholstered walls (all four walls) in a home theatre? Using the the fire resistant padding behind the fabric. Would this be a good idea or not?