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Discussion Starter · #1 ·
I am having some nasty echo problems in my basement theater. It is really apparent when I stand in the room an clap my hands. First some background on the room.


I have a new theater room in my basement. It measures 14.5x25. It is wood framed/sheetrocked with the normal fiberglass insulation. The ceiling is also drywall with the joists filled with fiberglass insulation. There is a support beam that runs down the middle of the room. It has been enclosed with drywall, extends down about 8" from the ceiling, and is about 6" wide. The floor is concrete covered with carpet/pad. I have 2 rows of seating. The second row is on a 10" raised platform. Both seating areas have a leather sofa. I am currently using Atlantic Tech 220 speakers in a 5.1 config. I will be upgrading to a set of Paradigm Monitors or M&K THX750's later this year. The room is a dedicated theater and will be used 100% for movies.


What I had planned to do was cover the front wall with some 21oz velour curtains. I was then going to use some Sonex acoustic foam or acoustic panels along the side walls to minimize the first reflection and the same along the middle section of the back wall. For the back wall I had planned to use either a 4'x4' or a 4'x6' panel centered on the wall.


Am I going down the right path? Will the drapes be enough absorbtion for the front wall? Anyone have any other suggestions? Thanks.


Gary
 

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I'm doing something similar with my room.


The front wall and the first 3 feet of the side walls will be covered with 2" InsulShield and the covered with GoM.


On the side walls and rear walls, I am constructing 2'x2' sound panels that I will place to cover off the first reflections.


I have no idea if this is going to be enough, but from everything I've read this should be good setup to start with. I can always add more sound panels/foam on the side walls.


But I do believe it is important to have good coverage on your front wall.


Also keep in mind that furniture, carpeting, etc will help a bit with the echoing.
 

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While I am not sure, I suspect curtains alone may not be enough.


What is important is how the material responds across a wide range of sound frequencies. I think I read that at low frequencies most curtains and carpets do little to kill the sound reflections.


I think the front wall is important for sound localization. If you are getting lots of reflections, then I think the stereo or 5.1 effect will be greatly reduced.
 

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 http://www.geocities.com/jonrisch/index2.htm


Jon Risch has some excellent DIY acoustic treatments you can make cheaply and are proven effective....If the Velour curtains do not handle the lower frequencies - then a few DIY Bass Traps will help.....


There are some reviews where a guy used Jon's DIY formula and compared them to Sonex & other purchased treatments and Jon's stuff outperformed the commercial applications.....Maybe you can get some help here. The best part is you can add as needed until problem solved....


Good Luck,

Dave
 

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Discussion Starter · #5 ·
Thanks for all the advice.


I did another experiment last night and the results are puzzling. When I stand in the front of the room and clap my hands I get what can only be described as an echo or some type of ringing. It appears to be coming from the side walls.


I then moved to the left side wall and clapped my hands again. This time I got more of a ringing and it definately appeared to be coming from the opposite side wall.


Is this a result of too much reverberation or is somethig else going on?


Does anyone know the NRC values of 21oz velour? I have also toyed with the idea of covering the front wall with acoustic foam and making some curtains out of GOM 701 fabric to cover the foam. Will using the GOM fabric in a curtain form negate its acoustic properties?


One last question...if I decide to go with velour drapes will the sound that is not absorbed be reflected or pass through to the wall behind the curtains?


Thanks again.

Gary
 

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You may find useful my Mediaroom spreadsheet for assessing the required absorption, areas and materilas to achieve the ideal RT60 for your room.


Use the link in my signature.


Good luck.
 

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What your getting is flutter. Absorbing the sound is part of it, but you will also need to diffuse it in some way (i.e. offset the sound waves so that you don't get two opposing/parallel flat surfaces.) Have you tried building your own diffusers? ;)
 

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What I did seems to work, but more by luck than judgement, as no acoustic measuring of any kind was done.


Like you, I did the hand clap test and had sever echo in my loft ht room before it was decorated.


I had read here that idealy you should have a 'dead' front wall, and 'live' rear, but the side walls should be dead from approx ear height down.


To achieve this, I covered the front (screen) wall with cheap black carpet,


I then covered the lower side walls with cheap grey carpet (to match the 18& Kodak grey decor), and used linning paper for the remainder of the walls.


Ceiling and rear wall was wallpapered using blown vinyl paper (because I liked the design!).


Echoes have now dissapeared and the acoustics seem fine to me at the volumes I listen at - around -20 on my Denon 3802 (room is 17.5 x 11.5 x 7).


Other people have done similar things, including carpeting the entire side walls. Jim MC is someone on this forum that inspired my final decision.

The Stargate


Pics are on my website if you're interested.


HTH


Gary
 

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Quote:
I was then going to use some Sonex acoustic foam or acoustic panels along the side walls to minimize the first reflection and the same along the middle section of the back wall. For the back wall I had planned to use either a 4'x4' or a 4'x6' panel centered on the wall.
Before you buy an "acoustic" product from anyone, under any brand name, insist on getting the test results from the appropriate ASTM testing for the acoustic benefit being suggested. If they are absorber panels of some sort, then demand the coefficients of absorption each 1/3 octave (NRC won't help you a twit).


If the manufacturer cannot or will not provide this information, then:


1. either the manufacturer doesn't have a clue as to what the product does, or the manufacturer does know and doesn't want you to find out;


2. if the manfacturer doesn't know, how is it you'd know the product will meet the needs you have (or even the needs suggested by the marketing);


3. you have to wonder if the product serves any acoustic purpose if the manufacturer refuses to submit the product for testing;


3. watch out for really stupid claims. Such claims are often found in white papers rather than marketing data for 'legal' (spell that FTC) reasons. One such claim for such a product is that it has a coefficient of absorption "over 1 for 650Hz to 20kHz". Bolder Dash! First no product is uniformly absorptive from 650Hz to 20kHz. Second it is impossible to have a coefficient of absorption greater than 1. Greater than 1 means the product is absorbing more sound than there is to absorb in the first place...in which case their next product will be based upon perpetual motion. (You might buy their stock, but not their product in that case.)
 

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Dennis is right about some of the crazy claims companies will make, definitely look for the technical papers or contact the manufacturer's engineering (not sales/marketing) department if you need to confirm some of the claims the product literature makes. As far as absorption coefficients >1, those result from the testing procedures, but are not consistent with most real-life applications. The >1 coefficients result from diffraction around the edges of the test sample which cause the sides to absorb sound also. The result of the diffraction is that you get the absorption of the surface, PLUS the absorption of the side of the test sample, but the area is calculated only for the front surface area (not including the sides), which results in a coefficient greater than 1. Most companies will print anything greater than 1 as just 1, whereas some companies will print the ASTM data as received from the lab. If you're doing calculations using those coefficients, you would just substitute 1 for any number greater than 1... unless you're into perpetual motion ;)
 

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John -


Thanks for that explanation - I was beginning to question my sanity, since both JM InsulShield & Certainteed Acoustaboard Black both list >1 on the specs of their thicker materials.


Bruce
 
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