Which Acoustic Insulation Should I Buy?

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MatrixClaw

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May 22, 2010
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Mesa, AZ
I'm sure not many of you guys are up on all the technical aspects of making DIY treatment, but to those of you who are, I was wondering if you could give me some insight into which of these materials I should buy.

I'm looking at building 6, 4" panels to treat my first and second reflection points (left, top and right), as well as 3 bass traps in the corners (the forth corner of my room is cut at an angle, where the door is, so there's no 90* angle there, just two 135* angles at each side of the door).

I have access to:

4" Roxul RHT80 (8pcf) - $1.30/sq ft
4" OC703 (3pcf) – $2.62/sq ft
4” OC703 FSK (3pcf?) – $2.59/sq ft
4" OC705 (6pcf) - $4.01/sq ft
4" Thermafiber SAFB (2.5pcf) $0.92/sq ft
4” Thermafiber Safing-unfaced (4pcf) – $1.28/sq ft

I was leaning more towards the Roxul, until they told me it was RHT80 and not 60. Is 8pcf too much for this sort of application (or would it work better in the application as a bass trap, more than a broadband absorber)? Otherwise, I'd probably go with Thermafiber on second choice, because it's significantly cheaper than the Owens Corning stuff. Unless the OC is really going to give me a huge improvement over the other two, I'd rather save some money and be able to get more of it if needed.

Which would you buy, and why? ;)
 
More density will almost certainly perform better at low frequencies. however, as thickness increases density becomes less important. Data for higher frequency absorption is quite easy to obtain on the internet
 
Actually, lower density works better for lower frequencies. You can use Roxul in your first reflection points and 703 for your corner superchunks.
And don't forget that you can treat your wall-ceiling corners too.
 
A few questions first:
1) What are the dimensions of your room?
2) Are all of the prices you listed for fiberglass of the dimensions 4” x 24” x 48” or are some smaller?
3) Are you limited to 4” thickness or can you get thicker/thinner sizes?
4) What type of basstraps are you planning on making (superchunks or straddling the corners with regular absorbers)?

A great place to find absorption data is bob gold’s page:
http://bobgolds.com/AbsorptionCoefficients.htm

If you can afford 703, it is always a good option because it is well tested and absorbs very well (assuming it’s an appropriate thickness for the problem, put in the right place, etc). If you’re on a budget, there are other options which work just as well as 703. For example, I used Roxul RHT40 (3.5 pcf) in my room for 4” and 6” thick absorbers, as well as 24” x 17” x 17” Studiotips Superchunks.

Conventional wisdom would suggest that RHT80 is a bit too dense to absorb well over a wide frequency range. However, the data on the page above suggests it would work even better than 703 of an equivalent thickness. The Thermafiber doesn’t seem to perform quite as well as RHT80 or 703, but at the price that it’s going for, you could buy twice as much and make 8” thick 2.5 pcf absorbers (which should absorb further down into the sub bass frequencies than 4” of any brand or density). This would be a bit of a gamble since there isn’t any data for 8” thick Thermafiber, but it could pay off if you’re willing to take the risk.

That said, if you’re truly limited to just the insulation types that you listed above, and want to play it safe, I would go with 4” RHT80 for the side reflection points and the cloud. Space these off the wall/ceiling by 4” and you should be golden. For the basstraps, it depends on the type/size of basstrap you’re planning on building.
 
Wisheraser said:
A few questions first:
1) What are the dimensions of your room?
2) Are all of the prices you listed for fiberglass of the dimensions 4” x 24” x 48” or are some smaller?
3) Are you limited to 4” thickness or can you get thicker/thinner sizes?
4) What type of basstraps are you planning on making (superchunks or straddling the corners with regular absorbers)?

A great place to find absorption data is bob gold’s page:
http://bobgolds.com/AbsorptionCoefficients.htm

If you can afford 703, it is always a good option because it is well tested and absorbs very well (assuming it’s an appropriate thickness for the problem, put in the right place, etc). If you’re on a budget, there are other options which work just as well as 703. For example, I used Roxul RHT40 (3.5 pcf) in my room for 4” and 6” thick absorbers, as well as 24” x 17” x 17” Studiotips Superchunks.

Conventional wisdom would suggest that RHT80 is a bit too dense to absorb well over a wide frequency range. However, the data on the page above suggests it would work even better than 703 of an equivalent thickness. The Thermafiber doesn’t seem to perform quite as well as RHT80 or 703, but at the price that it’s going for, you could buy twice as much and make 8” thick 2.5 pcf absorbers (which should absorb further down into the sub bass frequencies than 4” of any brand or density). This would be a bit of a gamble since there isn’t any data for 8” thick Thermafiber, but it could pay off if you’re willing to take the risk.

That said, if you’re truly limited to just the insulation types that you listed above, and want to play it safe, I would go with 4” RHT80 for the side reflection points and the cloud. Space these off the wall/ceiling by 4” and you should be golden. For the basstraps, it depends on the type/size of basstrap you’re planning on building.
Click to expand...

1. Here's some Sketchup drawings I did of the room, the layout and its contents:

studioroom_top.png


(Please note - The dimensions don't actually take into account the width of the walls, the dimensions you see are the inside dimensions of the room ;) )

studioroom_side.png


As you can see, I've got quite a bit in the room with my desk, as it also functions as my practice/jam room - The speakers in the corners next to my monitors are my PA system and I have 2 4x12 stacks along the long wall, with a small 2x12 cab along the short one. Obviously, the biggest item in the room is the drum set though. It's not the ideal setup, but it's what I have to work with for now until I move next year.

To be honest, my mixes translate fairly well and I don't have a huge issue with any particular frequencies (that I'm aware of), but I figure it's time to do some treatment, especially right now when I have dispensable income. The biggest problem I have right now, is that since I moved everything around (my desk used to be on the 13ft wall, with the 2 4x12s on either side, the 2x12 behind it, and the drumset in the corner where the 2 10ft walls meet), I've noticed a lot of unwanted echoing in vocal tracks I record, from what I assume is coming from all the reflection points from the bare walls.

2. Yes, they are all 4"x24"x48".

3. I can get them all in 2" as well, aside from the Roxul, not sure on that one, I didn't ask, as I was planning on just doing reflection points when I was quoted (with a 4" gap from the wall). The full price list I was given from the OC/Thermafiber supplier is:

703 board – 2 to 3 week lead-times
2” 703 board PLAIN – $1.38/sq ft
2” 703 board FSK – $1.526/sq ft
4” 703 board PLAIN – $2.62/sq ft
4” 703 board FSK – $2.59/sq ft
705 board – 2 to 3 week lead-times
2” 705 board PLAIN – $2.01/sq ft
2” 705 board FSK – $2.36/sq ft
4” 705 board PLAIN – $4.01/sq ft
4” 705 board FSK – Not Available
Mineral Wool (Thermafiber, rockwool)
2” SAFB (2.5pcf) - $.427/sq ft – in stock
2” Safing-unfaced (4pcf) – $.64 /sq ft (special order)
4” SAFB (2.5pcf) - $.92/sq ft (special order)
4” Safing-unfaced (4pcf) – $1.28/sq ft – in stock

4. I was actually planning on building membranes in the corners, after watching an episode of Pensado's Place, the acoustician on there said that superchunks really aren't effective in the lowend in small rooms, and that membranes are the only way to go. I'm still undecided, because there is a serious lack of membrane plans on the internet, but I'd kind of prefer not to build superchunks, because they are going to be very expensive, and potentially won't do as much as they would in a larger, more open room.
 
I've always heard 705 or something similar is best for bass trapping, and that's what I plan on getting for my own acoustic treatment. Especially since it does quite well on high frequencies as well. A panel in each corner with air behind it would be perfectly fine. You could use the 705 for that and 703 for your other purposes.
 
Have you measured the response of your room at your mix spot? I'm thinking that the window behind your mix spot will probably help minimize bass issues, but it's hard to say. You could help tame that flutter echo with the cheap 4" thermofiber stuff. Just arrange them sort of like a checker board on the side walls so that each absorber is facing a bare wall. Like this:

absorber wall absorber wall absorber wall ...
wall absorber wall absorber wall absorber...

I haven't learned much about more complicated types of room treatment like membranes or tuned absorbers, so I can't really help with that. The guys over at the John Sayers forum could probably help though.

EDIT: or maybe Mikas Mietshaus Akustik on this forum. He's the guy that designed jipchen's place.
 
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