Fireplace acoustic absorber for enhancement of the center stage

Fireplace acoustic absorber for enhancement of the center stage

Project:
Building a center stage acoustic absorber which will be placed above the fireplace and below mantel.

The concept is to allow sound waves in, have them bounce around a while in the cavity and dissipate energy. I placed some felt on the back face, about 30% of the open back exposes the brick, the perimeter is unsealed.

The traditional materials for this type of mid-band absorber is peg-board, on 2x4's wood studs with batten insulation infill. The pegboard gets covered with a fabric of course. You might see this high on the back wall of a church

A low and mid- range absorber would be a special hollow concrete block with holes or a slot in the face. the extra depth and density of the concrete allows the longer wavelengths to be contained and dissipated.

I also have rigid insulation covered with acoustic foam in the fireplace opening (behind the low center rack), some holes in the board to allow sound to get in, and hopefully trapped.

http://s184.beta.photobucket.com/user/kach22i/library/Stereo



Simple boxes and complex curves were sketched up, a form in the middle which could be easily built was settled upon. White school glue and painter's tape held it in shape at first. Later on, construction adhesive and foil tape at critical corners reinforced it all.

I was not 100% satisfied with the preliminary results, and the drill bits made a terrible mess of making holes. I used a soldering iron to make many more holes.





It sounded better now, but thought it was open to still more improvement, so I added the weather strip felting allow for some diffraction off the backing brick wall.




Here it is:






The sound is all cleaned up on vocals now, no extra sibilance even on heavily reverbed vocals. And the sound stage is complete, open and wide without the former patchiness.

DonH50 said:

Nice job, but why purple instead of brown?

I'm a little surprised it made a large difference with ESLs, since they have a null at the sides. I cannot tell depth too well from the picture; I assume they are far enough in front of the fireplace that the back wave is causing issues. In any event, a nice DIY project!

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Purple is an accent color in the house, in the carpet, couch, and record cubes I have nearby. The front side of the cloth is rather shiny, with a crepe paper like wrinkle to it, in direct light some pinkish hues come out. I rather liked the harem-like quality of it verses the backside which was duller, guilty of going for the glam and flash look it was just so pretty.

The plaster walls and windows are not as big of problem as the sonic glare of the brick, I'm not sure why this is so.

The speakers are 3-feet out from the plaster walls, and 7-6" apart center to center. I'm not claiming it to be as wide as heard from 12th row seat of the Hill Auditorium which I sat at last night for an evening of free classical music courtesy of the natural sciences department at U of M. However, it beats the pants off of the 4-feet apart I lived with for the 19 years prior.

I am thinking about installing heavy crushed velvet curtains with a rod secured to the ceiling to mask the TV screen with. It would look sort of tacky if done wrong, but could also look cool if done right.

GaryProtein said:

Fireplaces can be a bitch.

I boarded mine up too.

It hasn't seen a fire in decades.

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Fireplace and closets are a great opportunity for making bass traps in my opinion.

My fireplace has not seen a fire in 15 years, the 180 degree room swap was long overdue.

I'm interested in seeing what other people have done in similar situations.