Does 3M Super 77 reduce fiberglass mid/high absorption ?

Finally getting around to building my acoustic panels, most examples I've found here tend to use a wood frame for mounting and looks. I've read that leaving the fiberglass sides exposed offer even more absorption and I don't really need a frame. I've practiced glueing fabric to rigid fiberglass and get a good looking result, but it is somewhat stiff - any opinions on whether glueing the fabric (or 2 panels together) lessens the panels absorption for mid/highs ? - is this another reason for using a frame instead ?

gmore I don't have experience with them all, but used both brands (mostly Bostik) http://solutions.3m.com/wps/portal/3M/e ... 8HT14PGTgl http://www.bostik.com.au/distribution_p ... t_page.htm I have best experience with contact spray glue (looks as the type you suggested isn't a contact glue type). I'm not saying the others shouldn't work. In practice there are 2 types (from a practical type of view). Some spray glues spray a bit fluffy, other spray really fine. I like the fine spraying ones. If you respect the open time (contact glue principle) you can make nice work, without making the fabric stiff or without the glue penetrating the fabric. Sorry can't remember exact types and have no cans here with me. I'm sure other brands will/can work as well. For the absorption they are all OK. You never will use enough glue to really harm that absorption or you're working wrong with this stuff. I should go to your hardware or whatever store, ask which brands they have, ask for contact spray glue, ask if he knows if it sprays fine or fluffy, and take the fine spraying one with you at home.

Thankyou for the response and information. 3M Super77 is a spray - it appears fine when I spray - it seems to be whats recommended here in the states as well as being sold by suppliers of both the cloth and fiberglas. I've also tried a brand called Camie that was included with some acoustic foam I purchased. Both yield an attrative look, it just occured to me afterwards, that a harder surface may reflect more. I'm trying a lighter application to see if it makes a difference (at least by feel) - not sure what real test I can do. Thanks again. Dean

Dean, I know your type is a spray. The key point I referred to here is the contact glue spray. Since you spray both surfaces, you have direct good contact when still moisty. You need VERY little (a vague shade of glue). Once you bring both surfaces together (after respecting open time) you have a perfect connection. The only thing is that you must do it immediately right, because once connected it stays that way. But any spray you feel happy with will do. On the net people become keen on known types and brands. That's often just because they are repeated often enough. And 3M of course is a safe name (and expensive brand). It's a bit like OC 703 which became some kind of magic absorption standard, while being nothing more than a fiberglass board for which there are lot of valid regional alternatives.

3M super 77 is also a contact adhesive. We used to use it all the time back in the day when I was a car audio installer for custom speaker cabinets/door panels, for covering them with carpet. Same story, spray both surfaces, let dry for a bit, then stick em together. Works great.

Possibly, Strange is that 3M doesn't clearly say that in there own documentation, while doing it for other types. They do not describe it as a contact glue. (or I must read over something). I nowhere find that 2 surfaces must be sprayed. http://solutions.3m.com/wps/portal/3M/e ... 7/Super77/ I'm not saying it doesn't work that way. For me whatever glue that works clean is OK.

I've tried spraying cloth only or board only - both adhere very well, even with a light spray. Contact instruction offer spraying both surfaces only when an 'extra strong bond' is needed with a minimum 30sec drying time - i believe it implies both types :? . Did try a silly test :oops: blowing thru a dry peice of cloth (a test I've read for an acceptable cloth), and then a lightly, and heavily sprayed section (dry of course). There is a noticible restriction even when lightly sprayed - I assume once connected to the panel, the glue would dissapate some leaving more room to breath. I would have to think it would affect highs some, and a lesser grade burlap (am using a finer grade) would be less restrictive, but I'm guessing (hoping) that I'll probably gain more with an exposed glued side then using a frame, with no glue - just need to be easy on the spray. Thanks again.

gmore, If it works, it works, whichever glue. I've made at least 30 absorbers several months back gluing with contact spray at the edges and where needed. I had no problem whatsoever. I standard glued boards together 2*4 feet, and some of them I glued with 1 layer turned 90° to make stable 4*4 feet panels. If you have trouble now, I don't think it can harm buying another type (1 can) just to compare how that goes. I can not imagine that you should influence the absorption of that board in any significant manner, if you use not more glue than needed. Using your 77 or whichever typical contact glue spray (spraying 2 sides) will stick very well when applying it correctly. Maybe you have trouble by applying it only one-sided.

No problem on the application, although I've yet to do an entire panel. I had plan on spraying the entire face for a uniform look, but I'll try the edges 1st. My guess is the 1st couple of panels will be a mess, and then I'll have it down. Much appreciated :)

The 77 can actually be used either way - just as a one sided application (less permanent) or both sides as a contact adhesive. As Eric said, if you do the contact method and just spray the perimeter (and the back to wrap and stick), the vast majority of the absorbtion is untouched and functions just as though it just had the cloth in front of it. Bryan