Fireplace acoustic absorber for enhancement of the center stage

[kach22i]

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.

 

[kach22i]

It sounded better with the additional holes, 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:

 

[kach22i]

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.

 

[twich54]

Nice job George !

 

[zaphod]

Nice George, real nice.

on a thread of yours a thousand years back you and I discussed putting a big soft absorber between the logans to drop the soundstage. I built one for the old location, but i don't think it will work in the new room i'm building.

i've been thinking about a big 6x4 skyline diffuser between the logans on the back wall - thoughts?

 

[kach22i]

I've been thinking about a big 6x4 skyline diffuser between the logans on the back wall - thoughts?

I just did a little bit of research on the topic this morning because I was curious about the acoustic properties of the felt I used.

There are many examples and excellent PDF articles in this other forum thread which I've bookmarked.

http://www.gearslutz.com/board/studio-building-acoustics/604127-using-cork-sound-absorber.html

I would be very tempted to combine the Skyline diffuser with a DIY absorber backer.

What I mean is a 2x6 stud cavity partially filled with mineral wool or fiberglass board and backed with MDF or sealed to the wall, and using the Skyline mounted to the front face might be an awesome combination.

You would however have to provide a path for the sound waves to get in (the ones not being diffracted already). Which means drilling holes of various diameters into the face of your expensive brand new diffuser. The end result may not be to your liking, and not much resale value for a molested diffuser. However, if you are adventurous, go for it.

Imagine your diffuser is similar to the cork panel in the link. You need the gaps, holes or slots for sound to get in. They discuss the concept at length in the thread.

http://www.gearslutz.com/board/studio-building-acoustics/604127-using-cork-sound-absorber.html

If your room/equipment layout will not accommodate a large diffuser/absorber between the speakers, then I personally much prefer diffusion directly behind the speakers. Adding absorption between (center stage) the speakers helps the vocals and staging - my two cents.



If your diffusor is made of foam, use a soldering iron, but avoid the toxic fumes by doing it outside if possible and holding your breath.

 

[zaphod]

clever.

the use of dowels to create purposeful gaps is clever. i was planning on building the skyline myself, so hole drilling would also work. very very interesting George.

thanks!

 

[TomDac]

really nice, George!