How to choose foam for ceiling

ctviggen · « **on:** 2 Feb 2005, 05:01 pm »

My ceiling has a fan right near where the first reflection point is for my center channel and front speakers. I'd like to cover the part of the ceiling at the first reflection points and around the fan with foam, but I'm unsure of which type (wedge, pyramid, eggcrate) to buy. See:

http://www.foambymail.com/Products.html

Assuming the same noise reduction, does the pattern make any difference? Put another way, does the pattern also contribute to the noise reduction, so that I should focus on noise reduction and not the pattern? If so, what parameters for noise reduction should I be looking at? Should I look for very good high frequency absoption (as measured by NRC) for the first reflection points?

Thanks for the help!

John Casler · « **Reply #1 on:** 2 Feb 2005, 07:48 pm »

Quote from: ctviggen

Assuming the same noise reduction, does the pattern make any difference? Put another way, does the pattern also contribute to the noise reduction, so that I should focus on noise reduction and not the pattern? If so, what parameters for noise reduction should I be looking at? Should I look for very good high frequency absoption (as measured by NRC) for the first reflection points?
...

I think if you look at all the foams, the Wedge has the greatest acoustic value (generally by a small margin)

And call me anal (on second thought DON"T

) but I would say that the greatest absorbative properties would be had if the wedges are oriented to run "perpendicular" to the direction of the sound wave.

ctviggen · « **Reply #2 on:** 2 Feb 2005, 09:33 pm »

John,

That makes sense, as the wave would have to pass through a wedge (instead of parallel to the wedge). Now, I just need to figure out how to put it up onto a "popcorn" ceiling. (I do find it strange that the NRC numbers are greater than 1.0, when 1.0 is supposedly perfect absorption.)

John Casler · « **Reply #3 on:** 2 Feb 2005, 09:44 pm »

Quote from: ctviggen

John,

That makes sense, as the wave would have to pass through a wedge (instead of parallel to the wedge). Now, I just need to figure out how to put it up onto a "popcorn" ceiling. (I do find it strange that the NRC numbers are greater than 1.0, when 1.0 is supposedly perfect absorption.)

You might be able to use T-tacks or map Pins. I hang it on the wall with those. I place them in the "thinnest" (valley) part of the sheet.

ctviggen · « **Reply #4 on:** 2 Feb 2005, 10:10 pm »

Good idea!

davejcb · « **Reply #5 on:** 4 Feb 2005, 05:12 am »

I have that very foam on my ceiling, in 2" wedge format, installed perpendicular with thumbtacks.

Made a huge difference in imaging and focus. I decided to go with 2" versus the 4" I initially wanted because the difference is really mostly in < 500hz, and these aren't bass traps, these are installed to capture reflections, which are > 500hz.

Hope that helps.

ctviggen · « **Reply #6 on:** 4 Feb 2005, 02:08 pm »

That's a good point. I think that 2 inches might be better anyway, as I have a ceiling fan that the stuff will have to go around/underneath.

dwk · « **Reply #7 on:** 4 Feb 2005, 03:08 pm »

Quote from: ctviggen

John,
(I do find it strange that the NRC numbers are greater than 1.0, when 1.0 is supposedly perfect absorption.)

The reason is that the absorption coefficients are normalized to the area of the tile - ie per sq ft. However, since the tile has some thickness and the sides/edges are exposed to oblique waves, the total surface area that acoustic waves impinge on is actually much greater than the 1 sq ft area of the tile. On a 2" thick tile the face has an area of 144 sq in, but there are four side surfaces each 2"x12", or 92 sq in. Now, this doesn't completely add to the effective area, but it will certainly increase the 'cross section' as presented to the overall acoustic energy flow in the room.