[
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2008, Audio Asylum, all rights reserved ]
[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]
Welcome! Need support, you got it. Or share you ideas and experiences.
Return to Room Acoustics Forum by Rives Audio
58.179.88.188
In Reply to: RE: DIY acoustic panels questions posted by temporarymadness@aol.com on February 02, 2008 at 22:04:03
I tend to be against hybrids if you don't understand what you're doing. In this case you're actually combining 3 very different ideas.
The Jon Risch trap uses the paper backing of the fibreglass as a light membrane that's directly damped and Ethan uses the wood panel as a membrane that isn't directly damped but which is acoustically damped by the insulation which is spaced away from the membrane and is not in contact with it. By putting the backed fibreglass right up against the plywood, you're ensuring that plywood and the paper backing membrane mutually damp each other and that has to lose efficiency because you're going against the idea behind both of them as far as I can see.
I don't know what the idea behind the pegboard is in the third panel. The instructions I've seen for use of perforated boards also space it away from the insulation in a similar manner to what Ethan does with the plywood, and the perforations and space behind then act as a Helmholtz resonator with the insulation helping to give a more broad band response. While the insulation will damp the pegboard in this case so it won't act as a diaphragm like Ethan's plywood, the holes will allow sound to travel into the insulation where it will be absorbed. I suspect the real absorption, however, is being done from the other side and the pegboard may just be providing a stiff backboard for compression to increase the density of the insulation and allow it to absorb to lower frequencies.
Unfortunately a simple fact of life with these designs is that while they all may work, they don't all work in quite the same way. If you mix approaches you may certainly come up with something that combines the benefits of the different approaches, but you can just as easily—probably more easily—come up with something that negates the benefits of each individual approach and that is not what you want. Following a single set of instructions is a lot safer, is probably going to be more effective, and if you run into problems the person who provided the instructions will be in a better position to provide assistance.
I'd go with either Ethan's instructions or Jon Risch's, and build according to the instructions. Don't mix the plans. I wouldn't try the pegboard approach because I have no idea what the person who designed it intended to do with that approach but it isn't like the instructions I've seen in Everest's Master Handbook of Acoustics. Ethan, Jon, and Everest are all professionals working in the sound area with a sound knowledge of acoustics and at various stages I've learned useful things from all 3 of them.
David Aiken
i'd like to use jon's, but i have a couple issues with his:first off, he makes it sound like he's got rock wool panels exposed on the back. am i reading this wrong? isn't that stuff a mess? also, if it's that messy, wouldn't glue be silly? and if it's 1" thick, how can you staple it?
second, what the heck does "stapled at the edges to the middle side edges" mean? are there any diagrams for this?
sorry if i'm unreasonably confused about all this.
thanks always for your help,
-chris
3M 77 spray adhesive works great on rock wool. I've used it to attach burlap to Roxul 2" rigid rock wool boards for DIY acoustic panels. Spray the glue on both the rock wool and burlap, wait a couple of minutes for the glue to get tacky, then join the two. The rock wool boards aren't particularly messy; certainly less so than typical fiberglass insulation sold in rolls.
The easiest way to DIY 2' x 4' acoustical panels might be to use the "bags" from www.readyacoustics.com. These appear to be zippered cloth bags sized to fit over a standard 2' x 4' x 2" fiberglass or rock wool panel. Slide the bag over the insulation, zip it up, and you're done. I haven't used them but the bags look like a clever solution.
thanks. i'm assuming the answer is yes, but does the density of the roxul matter? if so, which one should i get?
-chris
I'm no expert so I can't really answer your question, but there's a useful chart of densities and NRC ratings vs. frequency for Roxul batts and boards and Owens - Corning 703/705 at the site linked below. I think I read a comment by Mr. Winer somewhere that rock wool and fiberglass perform essentially the same. I used Roxul boards and batts rather than the comparable OC stuff since the rock wool is about half the price of fiberglass.
I used to work in occupational health and safety before I retired. My understanding was that rock wool was less of a risk/problem than fibreglass. You can always cover the exposed rockwool with polyester batting as Jon recommends for the fibreglass. I would definitely cover the fibreglass.
There are staples that will staple through 1" though they may be hard to find. When I was at high school, I had a holiday job at Christmas and I used to staple up large cardboard cartons with those big copper staples. I can assure you that they would go through rock wool because one of them went through my right index finger, nail and all. Luckily it missed the bone. You need special stapling machines with the big staples since they don't fit the usual staple machines.
I have no idea what that instruction about the middle side edges means. Query Jon about it on the Tweakers Asylum board or email him directly. He's always responded to my queries so I have no doubt you'll get a reply. He may have a link to photos from someone who has built them.
David Aiken
on a post i made a long time ago, you said this:
"In any event I prefer to use polyester rather than Jon and Ethan's recommended fibreglass because of my background in health and safety. Fibreglass can present a health risk and I'd rather not use it myself in a DIY project."
can you tell me more about how these panels would be made?
-chris
I used polyester batts which were 430 mm wide by 1130 mm long (we're metric here in Australia so simply substitute whatever the measurements for your batts are.
I had a friend build me frames with an opening 1130 mm high and 860 mm wide so the frame would hold a double thickness of 2 batts side by side. Frame thickness was 100 mm, 4", which was about the thickness of each batt uncompressed. The frame sides extended about 15" below the bottom of the opening with cross pieces on the bottom (think inverted capital "T") for feet so they could free stand.
Across the open back of the frame I stretched and fastened a thin sheet of plastic. I sprayed spray adhesive onto the plastic and lay the first 2 batts side by side on top of the plastic, then sprayed them lightly with spray adhesive and lay the second pair of batts on top of them. I then covered the whole frame area with burlap. I lay the frame with batts in it on top of the burlap and tacked the burlap to the bottom of the lower crossbar of the frame. I then stretched the burlap tight up the back of the frame, over the top and back down the front pulling it as tight as I could, lay some board with a bit of weight on it on top to provide some compression of the batts, pulled the burlap tight and then tacked it to the bottom of the bottom crossbar on top of the starting row of tacks. Then I tacked the burlap to each side of the frame and removed the weighting. Panel finished.
The burlap provides the only compression and even though it is pulled tight and weighted during the covering process, it still bulges a bit once the tacking is finished and the weight removed. The end result is a panel that is 100 mm thick around the edges, the thickness of the wood, and thicker in the centre so looking at it from the side or from the top it will bulge in the middle slightly.
The plastic membrane seems to improve low to mid frequency absorption over simply compressing a double thickness of batts with wire mesh. You can improve absorption in the upper bass to mid area a bit more by replacing the first layer of batts with denser batts. We can now obtain quite dense (32 kg/cu metre = 2lb/ cu ft density) 50 mm = 2" thick polyester batts for soundproofing and home theatre use and they work quite well, either on their own with a think layer of normal polyester batting on top to provide some high to mid frequency absorption otherwise they're likely to be reflective at those frequencies, or as the first layer of batts with a second layer of more normal density batts on top. The dense batts are considerably more expensive here than normal polyester batts sold for thermal insulation, and they're still a bit more expensive than the normal batts when the price for an equal mass of each is compared. Despite that, if I were making more panels at this stage, I'd be using the denser batts for at least 1 layer and quite possibly for the second layer.
I have no idea how effective these are in comparison to any other design because I have only built them this way and I don't know anyone locally who has built any of the other designs for comparison. I also don't have the equipment to do measurements. They are quite effective when placed at first reflection points and they improve bass tightness in my room over and above the improvements I get with my DIY bass traps so they obviously seem to work down to a reasonable frequency, probably in the upper bass area, giving reasonably broad band coverage.
David Aiken
ok, yeah, polyester would cost way too much. so anyway, going back to your idea of a plastic sheet...assuming all this was in a wooden frame, would it be better to have (from back to front)
a) plastic/poly/fiberglass paper/fiberglass/poly/burlap
b) plastic/fiberglass paper/fiberglass/poly/burlap
c) plastic/poly/unfaced fiberglass/poly/burlap
d) plastic/unfaced fiberglass/poly/burlapthanks for all your help,
-chris
If I was going to use faced fibreglass and the facing was strong enough to handle the compression applied by a covering stretched tight, I would try the faced fiberglass with the paper tacked to the back of the frame and no plastic at all. A covering of polyester over the paper would be a reasonable safety precaution in case the paper splits at some stage and exposes fibreglass. I do think you need polyester over the front of the fibreglass.
I would only use polyester with unfaced fibreglass, and I would make sure that no fibres could escape between the plastic backing and the frame by both gluing and stapling the plastic down. You could then omit the polyester layer between the burlap and the plastic at the back of the panel but I would probably prefer to have some polyester there for HF to mid frequency absorption on that side also, otherwise the back of the panel will be reflective from mid frequencies on up.
David Aiken
in your second example, why does it matter if the back of the panel is reflective?
-chris
You get more absorption with the panel spaced off the wall and one of the reasons for that is that you expose a second surface for absorption. If you make it reflective, you lose some absorption efficiency at those frequencies where the rear surface is reflective.
Of course, if you only want the amount of absorption you get from the front of the panel it won't matter as far as absorption goes but the reflectivity at high frequencies coupled with the fact that it will still absorb at lower frequencies may create a problem with the tonal balance of the reflected sound field. Note that I said "may create", not will create, since that HF reflectivity has to be considered in the context of the overall reflectivity/absorption spectrum of your room.
David Aiken
assuming i went with the unfaced fiberglass, would you still recommend using spray adhesive (sticking fiberglass to plastic) in order to keep the fiberglass from sagging over time?
-chris
Yes, but not only to keep it from sagging. When I made my first pair of panels using polyester batts, I didn't glue them to the plastic. When I made the second pair, I did. My feeling was that I got better performance at low frequencies from the second pair. That's a judgement based on what I heard since I have no way of doing measurements.
David Aiken
thank you. your directions are quite clear. and as long as polyester isn't too expensive here in the states (which i have yet to look into) i think i'll be using your method.
-chris
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2008, Audio Asylum, all rights reserved ]