accoustics

[mtworkowski@o]

the reverb time in my living room has got to be .75 sec. Wall to wall carpet but 8' ceiling is a killer. also walls are relatively bare. I'd like to apply a foam to the ceiling to deaden the sound. What comes to mind on the ones that would attenuate the most sound. thanks

[FredGarvin]

How about starting with something a bit easier like fabric drapes on the windows? I don't know of any "fashionable" acoustic foam treatments for a home. The ones I know of are eggcrates that won't look too terribly nice but will work great.

Simply having a plain ceiling is not enough to overcome the absorption due to drapes, furniture and even plants.

[mtworkowski@o]

fred,
what i had in mind was the same as the 1/8 in. foam they roll out on your floor to put in an engineered wood floor. let's say 3 ft roll. white, hide the seams, wife is happy, reverb time goes to .1 where it should be. well?

[FredGarvin]

To be technical, the size of the foam usually has to be tailored to the major noise component. In other words, the size of the foam should be some characteristic length similar to the wavelength of the sound you are trying to eliminate. The only ceiling treatments I know of are

1) Drop ceiling tiles that are made of a specific absorbing material
2) a ceiling mounted on resilient channel.

Other buildings have used hanging absorption panels that are basically hanging panels wrapped in carpet. That would look a bit hokey in a home though.

I guess you could put foam directly on the ceiling. I just don't know who or where a foam is made that would look good.

[mtworkowski@o]

I found out that an open cell foam is not the way to go. but if the foam were white, flat, dull, and no seams, why would it look different than the ceiling I have now?
Whats the calc. on say 500 hz to 15000hz as far as wave length is concerned? c=720 mph @ sea level? wave length = fc? I forgot my 11th grade physics. It's only been 40 yrs. Go figure.

[mtworkowski@o]

Hey Fred.
You're probably sleeping. there's a KIT***** somebody over in the "torqe" heading of general engineering that has a Q. It sounds like your area. Good Luck.

[minger]

IMHO the simplest way to remember an equation is to write down your units and see what order they must be in. You know that there is some relationship between wave length \lambda, the speed of sound c, and frequency f.

\lambda = m

c = \frac{m}{s}

f = \frac{1}{s}

If you write :
\lambda = fc

Then you get:

m = \frac{m}{s} \frac{1}{s} = \frac{m}{s^2}

So you now realize that you must divide by the frequency:

\lambda = \frac{c}{f}

Which gives the correct units.

Plugging your numbers in gives wavelengths on the order from 2/3 meter, to 1/50 meter, depending on the particular wavelength you're trying to cut down (around 24" - 1").

[mtworkowski@o]

Minger,
Excellent. That is true about the formulae. Are you a teacher/professor? Very good.

[minger]

Nope, just 7 years of school and counting.

[bassplayer142]

Music studios have sound proofed walls to reduce the echo. Find a distributer for their foam because I'm sure they got all the physics of it worked out.

[FredGarvin]

I don't think most people would want to turn their living room into an anechoic chamber.