Need help with acoustic panels

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battleminnow

battleminnow

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We have had some great info in the past on DIY sound diffusion and absorption, but I am not quite finding what I am looking for. Here's the skinny...

I need about 10 4'x8' panels for sound absorption in a new church building, shell shaped, about 9000 sq ft. I would like to make them units that can be hung and removed if needed. I have read some threads regarding Knauff Fiberglass insulation, and like what I see. What are my options for building these and where can I find info? Someone said that burlap was the best covering, is that so? I would really like to be able to have murals painted on these panels and burlap doesn't seem real ideal for this. Thanks guys for the info.

Pete
 
Pete,

Try this link to Dan Merril's panels:

https://homerecording.com/bbs/showthread.php?threadid=42708&highlight=MDF+Panels

This may be what you're looking for. I've also seen versions of this without the MDF trays--just the board wrapped in fabric. The type of fabric I don't think is critical--you just want something that's fairly acoustically transparent. Burlap is used pretty often becuase it's cheap and durable.

From other posts on the subject I also gather that it's wise to wrap the fiberglass panels in plastic--so you don't get fiberglass dust settling on the pews.

If that doesn't do it, try to search the site posts for references to "clouds"; I recall seeing a few in the past.

Alex
 
Thanks for the quick response Alex. I had seen that before, and that was exactly what I needed. I do still have a couple of questions though...

1. Wouldn't wrapping the fiberglass in plastic eliminate some of the dampenning factors of the fiberglass?

2. If it is secured, would a regular insulation batt work if rolled into the area, cut to fit and glued down?

3. Where can an average person get ahold of Knauff fiberglass or anything similar?

Thanks,

Pete
 
Pete,

As I understand it, the plastic will not affect the absorptive properties of the fiberglass. From other posts as well as the frequency absorption chart at the SAE site, it appears rockwool has roughly equivalent acoustical properties to fiberglass board. You can probably locate either at a commercial/industrial insulation supply dealer in your area. Try going to the manufacturer's website, get the contact number, and call and ask them for a list of stores in your area. I've had good success with this approach with Knauff and Thermafiber--not such good luck with the guy I talked to from Owens-Corning (he intially referred me to Home Depot, then when pressed, gave me numbers to a bunch of stores that didn't carry what I was looking for).

Alex
 
I would think that would depend on the use. In Everest's books, he shows two different low freq absorption figures for spun fiberglas when used outside a wall as an absorber, one with paper in and one with paper out. Here you're talking about semi-rigid, and plastic, so I don't know how much difference you'd see. I can't help thinking that there would be a difference though... Steve
 
I built about 30 of these 2x4 panels for my church a while back. Our building had a huge flutter problem between the side walls as well as a front to back echo. The back wall is maybe 75 feet from the stage.

Some notes from making them:

1- if making a lot of them, set up up jigs for drilling and cutting to keep everything consistent, it makes assembling them and installing them a snap. also predrill the MDF or it will split.

2- Cutting MDF makes a ton of dust. Also, I prefered working with the white melamine MDF instead of the brown MDF when available.

3- Cutting the fiberglass board is easy. wear a mask.

4- if you have a friend with an air stapler to put on the fabric, borrow it!!

5- The fabric cover will hide a plethora of mistakes.


I predrilled four holes through the long sides of the frames and hung these panels with long drywall screws into small plastic drywall anchors. Home depot sells little plastic drywall screwhead covers covers that snap into the heads of drywall screws, and since they had to look good i sprayed them first to roughly match the panel fabric cover. I suppose you could also put a picture wire on the back of the panel and hang them if desired.

personally, I think wrapping them in plastic and fabric is overkill, unless you're using a really open weave type of fabric. I have not found the fabric covered fiberglass to be a problem.

About their sound ablilties:

these babies soak up sound. Put them on a wall, stand next to them and it's like a vacuum for sound.

I staggered the mounting positions of these on opposing walls ( no two are exactly opposite of another thus breaking up as much of the parallel wall relections with the least number of panels) I was able to tame a great deal of the flutter in the room.

The fiberboard is rated down to 500hz and even somewhat lower, but in this room I feel that the 500 region is still a bit stronger than I'd like it. Not quite sure yet if this is a function of the room or the fequency response of the panels. I may replace a few of these panels with some sort of slot absorbers, to give me some low-mid absorbtion and more diffusion.

Also, I would suggest that users consider what they are trying to accomplish with these panels as they can drastically affect your room sound- for better or worse...
 
Also, although I've not tried this, I think a bargain version might be made, as Alex said, by glueing the fiberglass board to something like an 1/8" pressed board backing panel and wrapping it in fabric. This would be ultra light and perhaps easier to hang and handle. The trays I've built really only provide for a nice clean frame with square corners to staple the fabric to. I don't believe they add much acoustic value to the panels.
 
Thanks for all the replies guys. I found a dealer of rockwool in the area (it took me a few days) and the prices are great. I can't wait to get started. I have to wait until after the carpet goes in on the 26th, and then I'm on it like a fat kid on a hoho.

Pete
 
Hey Dan,

For your problem with 500hz, you can build a box about 6" deep and put R19 fiberglass (not 703) with the facing out. This creates a broadband Helmholtz resonator tuned with absorption numbers that are approximately:

125 (.4) 250 (.8) 500 (1) 1000 (.6) 2000 (.4) 4000 (.3)


These numbers are from memory, if anyone has their "Master Handbook of Acoustics" handy and could check those numbers it would help.

I found these absorbers in that book and made a bunch of them to treat my temporary studio, because I couldn't find a local source for 703. They work very well, and will target what you need.
 
thanks eric. a good suggestion and workaround if no 703 is handy, but you gotta love the absorbtion of 703 at a mere 2" thick! And 4 inches of it is amazing...
 
Acoustic panels vs. slot resonators?

Hi, can someone explain the difference between the two, and the advantages of each maybe? I thought the resonators did the same thing!
fitz
 
Fitz,

The panels are good for highs and some mid-frequencies--from the posts above it looks like about a 500 Hz cutoff. A lot of rooms have problems with lower freqencies building up. To catch these, you need a resonator or trap.

Alex
 
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