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DIY: Minimize Reflectivity in new HT room


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5 replies to this topic

#1 of 6 OFFLINE   Jason Burgess

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Posted May 21 2003 - 10:53 AM

Hi folks,

Please excuse me if this topic has been beaten to death.

After buying a split-entry home last year, I have dedicated a basement room to my HT. Dimensions are 23'x13'. There is a 3.5'(h) x 11" (w from wall) wood paneling acting as a decorative cover for the foundation which runs along the front, right and rear walls. The remainder of the wall space (the unpaneled portion of the front, right and rear + all of the left wall) are painted sheet-rock.

The room has many reflections which I find are making the sound and dialog very clouded. Effects from the rear speakers tend to reflect off the front wall, distracting from the discrete nature of the 5.1 system. Also, the dimensions of the room just about break the golden rule of standing wave prevention.

I am looking for some cheap ways to lessen the reflections in the room. I was thinking the simplest start would be to hang some very heavy drapery material. However at around 560 square feet (70ft of wall space x 8 feet high wall) of drapery material, this might get costly. Posted Image

Currently, I am interested in taming the reflections in the room. I'll tackle any bass issues later. They are far less distracting to me at the present. Any suggestions would be appreciated. There is a Home Depot nearby, so any DIY projects are also welcome. Posted Image

Cheers,
Jason

#2 of 6 OFFLINE   MikeWh

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Posted May 21 2003 - 01:27 PM

If you don't want to spend all that money to cover the entire room with heavy drapes, then I'd suggest that you concentrate on the hot spots. Specifically target the points of reflection in the room-- sit at your normal viewing position and map out the reflection points as they would eminate from the various speakers. If you can't eyeball these points, there are various techniques and tools to help. You'll have to search around here.

Heavy drapes, tapestry, oriental rugs... all are good for this. Alternatively, you can make your own acoustic panels. My father-in-law did this in his HT to completely eliminate the reflections from the infamous clap test. Find some high-density sheet foam rubber (ultra high-density, if you can find it.. it's more expensive though) and tack-glue it to a simple frame of wood. Stretch and staple some fabric over the foam panel. This is a fairly inexpensive acoustical treatments AND can be designed to blend in with the decor of your HT. If you don't want to make your own frame from scratch, go to a crafts store and purchase the wooden stretcher frames used by painters to stretch their own canvases.

Good luck.

#3 of 6 OFFLINE   JakeMcM

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Posted May 21 2003 - 06:28 PM

I made acoustic panels in only a few hours. I got some 1x4's and made a frame. I attached them with some mending plates so that it was like a bottomless box, then I cut some 3 more pieces to go down the lenght of the frame. one in the middle and the other two on the sides for support and places to staple etc.
First cover the back with some polyester batting that can be had cheaply at most any fabric store. Then glue, or staple at least six inches of faced insulation (paper side down...sorry if too obvious.) onto the frame. Cover the insulation and the sides of the frame with some more polyester batting.

At this point you have polybatting, then the insulation, then more polybatting...you don't want any of the insulation exposed.

Then cover the front with acoustically transparent cloth (essential) I used speaker grille cloth but burlap would be cheaper. So now I have two 30" wide and 5' 6" tall panels that absorb hopefully down to about 100hz. Its also important that the panels be spaced as far out from the wall as reasonably possible...I would say 6 inches would suffice. If the panels are two close to the wall the panels won't absorb the lower frequencies and this can severly affect the balance. Its also important you use at least 6 inches of the insulation for the same reason. You should strive to make your panels as full range as possible.

I got this information off of Jon Risch's website. These panels work and are pretty cheap I think it cost me about 50 bucks for both and they are big as far as panels go.
The soundstage isn't so smeared anymore, when a sound goes across the speakers it sounds a lot better, before I didn't really hear that effect, its quite distinct now but not too distinct or localized...just like I like it.

In my opinion carpet, and drapes aren't going to do it if you have a lot of reflections, they might work in non essential places, or places where you don't want a lot of absorbtion but the side walls at the first reflection point is where you need some pretty heavy absorbtion...or diffusion if you can afford it.

#4 of 6 OFFLINE   Jason Burgess

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Posted May 22 2003 - 01:55 AM

Hi folks,

Thanks for the excellent information. The next obvious question would be how does one calculate the main points of reflection in the room? I heard once that you can use mirrors in some fashion.

#5 of 6 OFFLINE   Reid_d

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Posted May 22 2003 - 02:36 AM

http://www.recording...sers/acoustics/

http://www.geocities...jonrisch/a4.htm

Seated in the listening position slide a mirror down the side wall at tweeter height. When you see the speaker in the mirror thats the 1st reflection point.

#6 of 6 OFFLINE   TimForman

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Posted May 22 2003 - 10:49 AM

In a similar fashion as acoustic panels I'm going to put acoustic foam on the walls then hang inexpensive (thin) drapery material over it for looks.