prk@charm.UUCP (Paul Kolodner) (09/15/85)
new topic net.audio I would like to introduce a new topic: arranging a listening room for best sound. Here's an area where hard facts are hard to communicate because rooms are not sold, but clearly, the biggest thing you can do to change the sound of equipment you liked in the store is to take it have and install it there. Who can communicate general principles to help me improve the sound of my living room? My living room is the front third of an open space 15 ft wide by 50 ft long. The front wall (15 ft wide ) has two windows covered by floor-to-ceiling heavy curtains. The speakers are two ft in front of this wall, about 5 ft apart. I sit about 10 ft back. The wall on my left is plaster in front of me and is blocked by a large bookshelf behind me. The wall on my right is brick in front of me (a fireplace) and is covered by a floor-to-ceiling bookshelf behind me. Behind me is about 40 ft of empty space. The floor is wood, with a 4ft by 6ft area rug right between me and the speakers. The furnishings include a heavy sofa on my left but nothing else that absorbs sound. There are a number of features of this space which might have an effect on the sound, but I'm not sure about WHAT effect. First, the space in front of me is asymmetric from left to right. Second, NO reflections come from behind me; in fact, the rear wall is actually at a noticable angle from the side walls; this is apparently quite common and deliberate in old houses - keeps the reflections down and the place is quiet. Third, behind the speakers is a mass of heavy material which presumably absorbs high-frequency sound. Fourth, the speakers seem to be coupled well enough to the floor to let me feel the bass notes in my feet. This space is acoustically dead, despite the presence of hard, reflective materials and the absence of absorbers. When I snap my fingers or clap my hands, no ringing is heard, presumably due to the large size of the room and the slightly angled walls. If I do the same thing in my bedroom, it rings quite a bit, because the carpenter put in straight, true walls; this despite heavy carpeting, heavy drapes, a big bed, a chair, and other absorbers. So now the questions. Does one want the speakers to be coupled or decoupled from the floor? Do large left-right asymmetries have a bad or good effect on the sound? Does one want reflections from the side and the rear? In concert halls, reflections are good, but that's not very relevant here. Does one want a reflector or absorber behind the speakers? Suppose I do what my wife wants me to do: put the speakers on either side of the brick fireplace on the right wall and sit on the sofa on the left wall. This would put a 40-ft deep empty space on my right and a wall on my left. Is such an asymmetric arrangement a bad idea? (I'm going to check it out this week.) I have spent some time describing the details of one room that most of you will never see. However, I hope that the specific questions I just asked will generate some information of GENERAL usefulness to us all. If this results from YOU giving ME advice about MY room, great!
tommie@psivax.UUCP (Tom Levin) (09/17/85)
In article <748@charm.UUCP> prk@charm.UUCP (Paul Kolodner) writes: >I would like to introduce a new topic: arranging a listening room >for best sound. Good topic. >So now the questions. Does one want the speakers to be coupled or >decoupled from the floor? One wants the speakers to be rigidly coupled to the ground, preferably on very sturdy speaker stands. Speaker stands are important to "clean" up the bass. For best stereo imaging, it is also important that the stands don't move. People in this group have suggested "tip toes" which are metal pyramids that you put under your stands with the point down. This "digs" them into your carpet making them very sturdy. Of course, driving nails through your speaker stands will also get a nice sharp tip to dig into the carpet. >Does one want reflections from the side and the rear? >Does one want a reflector or absorber behind the speakers? The "hot" listening set-up is what's commonly called a "live end, dead end" room. The area behind and directly in front of the speakers should be as acoustically "dead" as possible. The area behind the listening position should be "live" (i.e. glass, walls, etc.) One company that advertises in many stereo magazines (Audio for one) sells foam pads called Sonex. They should be put on the wall directly behind the speakers. They cost $40.00 for a package of 4 pads (I think they are 2 ft. squares). They do look pretty ugly though. You might want to just put up real thick curtains or even a large tapestry with fiberglass stuffed behind it. >Suppose I do what my wife wants me to do: put the speakers on either side >of the brick fireplace on the right wall and sit on the sofa on the left wall. >This would put a 40-ft deep empty space on my right and a wall on my left. >Is such an asymmetric arrangement a bad idea? While this might make your room more attractive, it would be disastrous acoustically. You should *never* listen to your wife! :-) :-) :-) :-) :-) >I have spent some time describing the details of one room that most of you >will never see. If you invite us all over for a "listening" party then we can see your room. (-: PARTY AT PAULS!!! :-) ========================================= | LIVE DEAD | S - Speaker | D S D| * - Your listening Position |LOTS OF REFLECTIONS L E E| |ARE DESIRABLE OVER I * A A| |ON THIS END OF THE V D D| |ROOM! E S | | LIVE DEAD | ========================================= -- __________________________________________________________________________ Tom Levin {ttidca|sdcrdcf|logico|scgvaxd|bellcore}!psivax!tommie You've seen those car stickers that say "Baby on Board"??? _________ I want one that says: / \ / Psychotic \ / On \ \ Board / \___________/
prk@charm.UUCP (Paul Kolodner) (09/24/85)
I'm delighted that someone read my posting about my living room enough to actually respond. I have some new data. This weekend, I moved the speakers in front of the fireplace. For those of you who did not memorize my posting, this means that I now sit with my back to a plaster wall. The spaekers are in front of me, with a wall of brick behind them, there is a plasterboard wall with floor-to-ceiling curtains on my left and forty feet of empty space on my right. How does it sound? TERRIBLE! The high frequencies are gone, and there is a boominess in the lows that is quite pronounced. The sound is quite a bit more constricted and closed-in. The old arrangement sounded much more open and airy. My colleague, Dr. Femtoblatt, and I deduce that the high frequencies are being sucked up by the space on the right and the drapes on the left. The brickwork behind may have had little effect - the speakers don't radiate out the back anyway. In this case, he suggested that the acoustical properties of the wall behind the speakers are not important; I have not noticed much difference with the drapes closed or open when the speakers are returned to their original positon in front of said drapes. By the way, I have heard of Sonex acoustical pads. They sound like a rip-off. I have spent some time surveying the market for acoustical materials, mostly in connection with noise control in my house. There are several companies which make acoustically absorbing foam, and it can be quite a bit cheaper than the amount mentioned. There are also many other materials for damping, isolation, and absorption on the market. I wouldn't go slathering anything on my walls until I had a serious discussion with a technically competent acoustical engineer. I happen to know just such a person, who works for a distributor of acoustical materials, and I will be glad to give his name and number to anyone who is interested enough to send me mail.
djb@riccb.UUCP (Dave J. Burris ) (09/24/85)
> By the way, I have heard of Sonex acoustical pads. They sound like a rip-off. > I have spent some time surveying the market for acoustical materials, > mostly in connection with noise control in my house. There are several > companies which make acoustically absorbing foam, and it can be quite a bit > cheaper than the amount mentioned. There are also many other materials for > damping, isolation, and absorption on the market. I wouldn't go slathering > anything on my walls until I had a serious discussion with a technically > competent acoustical engineer. I happen to know just such a person, who > works for a distributor of acoustical materials, and I will be glad to > give his name and number to anyone who is interested enough to send me mail. While Sonex(tm) foam is a little expensive, I think if you make a comparison of the absorbtion characteristics you will find Sonex far superior in it absorbtion vs. frequency characteristics. Especially if you get three inch or greater thickness. Typical sound absorbtion materials used in building have somewhat erratic frequency responses that are usually centered in the speech range (~300-500 Hz.). If this is where you need your absorbtion then you are in business. If not, well... Remember, frequency compensation through absorbtion may not even be practical. Absorbtion is generally used only to correct for a RT60 time which is too great (often frequency dependant) causing intelligibility loss, not for frequency response caused by poor room dimensions and construction. In most cases abrorbtion does NOT substitute for frequency equalization. If you know someone who owns a real-time analyzer, you can isolated poorly braced walls which cause dips in the low frequency response due to parasitic oscillations. Solution: use screws rather than nails and use plenty of them. I would highly recommend the live-end/dead-end approach for discriminating listening. This method was documented by Don Davis and has proven to be the most popular for studio and control room monitoring. The speakers are placed in the dead-end which has a high absorbtion over a wide frequency range. The opposite end of the room is reflective but also diffusive to eliminate standing waves. The listening position is arrived at by experimentation and somewaht by preference. Many studios even purchase expensive diffusion plates for the live end of the room. For home use much compromise is required but working around this concept is an excellent starting point. -- Dave Burris ..!ihnp4!ihopa!riccb!djb Rockwell Switching Systems, Downers Grove, Il.
seifert@hammer.UUCP (Snoopy) (09/25/85)
In article <761@charm.UUCP> prk@charm.UUCP (Paul Kolodner) writes: > The brickwork behind may have had little effect - the speakers >don't radiate out the back anyway. In this case, he suggested that the >acoustical properties of the wall behind the speakers are not important; >I have not noticed much difference with the drapes closed or open when >the speakers are returned to their original positon in front of said >drapes. I would expect that the reflection/absorbtion qualities of the wall behind the speakers to be less important than the qualities of the walls, floor, and ceiling immediately in front of the speakers. (for "conventional" speakers only, this doesn't apply to Bose, Magnapan, etc) How solid the wall is will effect the bass. Solid walls such as concrete, are prefered to flimsy walls, such as 1/8 inch paneling tacked to 2x4s. [ People looking for an argument will please note the difference between saying "less important" and "totally unimportant". Thank you. ] Snoopy tektronix!hammer!seifert tektronix!tekecs!doghouse.TEK!snoopy