Resonance problem with sliding glass

Brian Scheffer · Post by **Brian Scheffer** » Tue Feb 14, 2006 10:40 am

Sibirdoug, the entire booth including the ceiling is covered in 5.5" acoustical cotton, so I think I'm ok there. I had a bass cab in there and discovered that an a flat passed right on through. I'm not sure what the Hz equivalent is exactly. I can certainly run tones and find out exactly what it is. What sort of pressure sensative adhesive would you suggest? I was told by the company that makes the clear MLV that I'd have trouble finding an adhesive that would dry clear. If I do sections of damping it doesn't necessarily have to be clear.

Sibirdoug · Post by **Sibirdoug** » Wed Feb 15, 2006 3:53 am

Brian:

You are right, 5.5" acoustic cotton should do a pretty good job based on the dimensions of your booth. By the way what is the height of the booth?

I want to be clear on something else, somebody mentioned A-220, do think it’s within that range? Is there higher frequency ringing as well?

Most pressure sensitive mounting adhesives are acrylic based and do a pretty good job at damping with a constraining layer. They won’t be totally clear but translucent none the less. Industrial supply stores should have it. Mcmaster Carr might have what you need wwww.mcmaster.com/

Brian Scheffer · Post by **Brian Scheffer** » Wed Feb 15, 2006 6:10 am

The booth has a canted ceiling. It's canted in two directions. It goes about 7.5' at its lowest to 10' at its highest. There is definitely a higher octave ringing in there as well. The link you sent is a bit daunting to navigate for someone like me who knows very little about construction. I found some Glue Discs that are clear (catalog #7187A21). Is that something like you suggest?

Sibirdoug · Post by **Sibirdoug** » Wed Feb 15, 2006 8:03 am

Those adhesive discs might work. I think they are worth a shot- you will need to use lots of them. The more surface area the better. If you have say 8"x 8" pieces of plastic you should use one for every two inches on the plastic. Speaking of plastic, the thickness should be greater than the glass. The idea is to try to match the bending stiffness of the plastic to the glass.

I'm just shooting from the hip here but you should plan on covering the about half the glass with clear plastic. Try right in the middle first. If that doesn’t work place them all over. If that doesn’t work, try doubling up the adhesive.

Brian Scheffer · Post by **Brian Scheffer** » Thu Feb 16, 2006 12:33 am

I'm trying to get your idea straight, Sibirdoug. What you're suggesting is that I get some regular plexi glass that's thicker than the 1/8" glass and cut it into sheets about 8" x 8" square and attatch them to the glass with the glue discs from mcmaster.com. I should cover about half of the surface area of the glass. Is that the gist of it? What if I cover the whole surface of the glass with a layer of plexi? Would that lead to better performance? I'm thinking that a layer on top of the entire surface will look better than squares here and there.

I'm also seriously considering filling the fixed side of the frame with sand. I'd still have sight lines through the sliding portion and I'd have half as much noisy glass to worry about. Is this a crazy idea? I figure I can drill a small hole in the frame, fill the thermal break with sand and kill that resonance dead. Is there any reason this wouldn't work?

Sibirdoug · Post by **Sibirdoug** » Thu Feb 16, 2006 4:26 am

You have the gist Brian. You could cover the whole thing, certainly! I was thinking from a visibility standpoint. You might want to look at cutting the plexiglas in half to make if easier to remove. Keep in mind constrained layer damping (CLD) methods are part art and science just like acoustics so it will require some experimentation. So don't give up if it doesn't work very well the first run.

Before filling the one side with sand, try this: It occurs to me that you could drill many large holes of different sizes (the same size creates it's own resonance) in the sides to release the pressure between the two pieces of glass. This should diminish the air gap resonance. If you make the holes big enough stuff pieces of foam in them. You could do this to both sides and if it screws things up, fill the holes with clear silicon cocking. Do could do this before anything else.

If you go with sand in the other side fill it a ¼ of the way and listen, then some more until you are satisfied. Keep in mind sand will have less effect on the higher octaves.

I would like to hear how your project goes, so this my e-mail address: dougg@soundkinetics.com