Resonance problem with sliding glass

Brian Scheffer · Post by **Brian Scheffer** » Fri Feb 10, 2006 1:48 am

Hello everyone, it's my inaugural journey into poting on this fine message board. I've already found a ton of useful information. Thanks for making this a great site, everyone. On to the business...

I'm in the process of building my first legit studio here in the city of St. Louis. The space was a studio before, so we're ahead of the game, but they did take some things with them. The studio has a live room with two iso booths. The booths were separated from the live room by a single sliding glass door. The original tenets took the doors with them, so we replaced them with two sliding glass doors per iso. The problem I'm having is with the glass ringing in a nasty way. We didn't notice the issue at first since the booths were untreated and rather out of control and reverberant, but now that we've deadened what is destined to be our vocal booth, we've noticed that even at moderate volumes (i.e. loud talking) the glass gets ringing. I definitely see it as problematic in a show stopping way. The room is rather small (roughly 7 x 5 x

, so there's no getting away from the doors.

I'm wondering if anyone has any suggestions as to what I can do to minimize the issue. We've been lead to believe that the problem is a function of the airspace between the panes of the glass in each door itself and not a function of the airspace between the doors. The doors are thermal break, with 1/8" glass, a 3/4" airspace, and another 1/8" of glass.

I suppose I should have anticipated this resonance with a large thin pane of glass, but I didn't. Live and learn...

I'm guessing that some sort of dampening is my best bet, but dampening the glass even with a significant portion of my body will make the decay time faster, but the ring is still present. I need some outside the box thinking. I certainly would hate to lose money, time, and morale having to tear the damn things out. Save me, message board!

knightfly · Post by **knightfly** » Sat Feb 11, 2006 7:09 am

Let me guess, they ring at around A-220, right? That's the msm for two 18" glass with 3/4" gap.

Only thing short of replacement with two heavy, single pane sliders that I might try would be some of the stuff that's laminated onto auto glass for tinting; but I doubt it would do much if damping it with your body doesn't do much - Sorry, but that's a tough one - maybe get one of those suction cup glass-lifting devices, and hang it on one side of the glass during takes to change one of the panes??!? ... Steve

Brian Scheffer · Post by **Brian Scheffer** » Sat Feb 11, 2006 7:49 am

A fine guess, sir, about the A-220. Something tells me that you may have used something like, oh I don't know, SCIENCE to figure that one out! It actually seems to be an A flat, but I'll give you an A+ anyway. My measurements are probably a hair off.

I happen to have one of those suction cups around from when we installed our control room glass, so I'll run an experiment. Now, should I dampen only one side of the glass? Will that be more effective than dampening both because it will give the panes different characteristics?

As far as replacing the glass goes... I was actually looking for single pane doors in the first place, but didn't really have any luck. Is such a thing readily availible from a source I must not have found? I was told by a door guy (not the kind that checks your ID) that I'd never find a door like that with a 1/2" piece of glass in it.

I was told that argon gas filled doors would help some with this issue. I suppose that that's not going to happen after market, however. The only other idea I've been seriously entertaining is putting a heavy drape or a drape with mass loaded vinyl sewed in that I can pull in front of the glass. That way I'm cutting down on how much sound will be exciting the glass and how much the resonance will be flying back into the room. I really feel like my hands are tied here to a certain extent until I can afford to get something else in there.

Unless.... A crazy idea that I was given in jest is to fill the gap with sand. If only these sliding doors didn't have to slide......

Another wacky idea I had was to perforate one side of the glass, which would cut down on my (already poorer than an effen solid core door) isolation. I'd imagine that to get rid of the resonance, I'd have to perforate it to a point that structural integrity is an issue.

Is there a magical barrier semi-permeable to people and not sound that you guys know about and you're holding out on me?

knightfly · Post by **knightfly** » Sat Feb 11, 2006 8:21 am

Suction cup - one side only, because of what you said.

Glass - try a local glass shop for the possibility of replacing your glazing with 3/8" and 1/2" safety glass; probably cheaper than finding $4k doors with that in them. IF your doors are "cheapo", the rollers/track might fail prematurely with that much weight though.

Argon - speed of sound in Argon is only a few FPS slower than air, probably lower your resonance a semi-tone

- also, retrofit isn't possible. Most argon filled units are a single, hollow, SEALED envelope of glass IIRC.

Perforation - you're kidding, right??!? IF you have the time it would take to "micro-perforate" just one side of your doors, I'll send you plane tickets and you can spend that time working for ME for $.02 an hour

Magical barrier - I'd tell ya, but then I'd hafta kill ya... Steve

Dan Fitzpatrick · Post by **Dan Fitzpatrick** » Sat Feb 11, 2006 9:53 am

transparent aluminum

knightfly · Post by **knightfly** » Sat Feb 11, 2006 10:00 am

Perforated spent Uranium

(OK, now I'm gonna hafta KILL ya)

andy_eade · Post by **andy_eade** » Sat Feb 11, 2006 12:58 pm

you know, you can buy transparent MLV. soundsuckerssell it. I wonder if you could somehow laminate this to the existing glass?

knightfly · Post by **knightfly** » Sat Feb 11, 2006 1:03 pm

The versions I've seen (industrial "sound curtains") are more transLUCENT than transPARENT - I'd think it would be kinda tricky to get all the bubbles out and choose the right laminating adhesive... Steve

On top of which, if holding various body parts against the glass doesn't help, I doubt that much else would either

Brian Scheffer · Post by **Brian Scheffer** » Sat Feb 11, 2006 6:48 pm

I forgot that you can get clear MLV. It seems like that could help. Damping the glass with my torso region did cut the decay time in half I'd say. It couldn't hurt the situation. Knightfly, that's a good point about the adhesive, though. It'd be like a bad self-tinting job in a car if I wasn't careful. What do you guys and gals think about the feasibility of this idea? Will it give me a result worth the money it would cost?

It's this or the Uranium. (wink.)

knightfly · Post by **knightfly** » Sat Feb 11, 2006 10:18 pm

It would be cheaper than having your doors re-glazed, but I'm concerned about compatibility of materials. I doubt the place with the clear MLV has adhesive that's designed to laminate to glass (ask them, you never know) and the car glass tint places are unlikely to be able to tell you if their adhesive will be compatible with the MLV - the tint stuff is probably MYLAR, so who knows? You could end up with a total mess because of chemical incompatibility.

About all you could do is ask for samples of the clear MLV and order a small kit from a car window place, get a piece of glass and try laminating the MLV to the glass. A hard rubber roller will help, I used to have one for rolling prints onto a ferrotype print dryer, back when "glossies" were "in", but not sure where you'd find a larger one... Steve

Brian Scheffer · Post by **Brian Scheffer** » Sun Feb 12, 2006 8:41 pm

I shot an email off to the company that makes the clear MLV and asked them about a recommended adhesive. I'll keep you all posted if I hear anything.

Today I tried putting some suction cups on the side of the glass in the booth, and it did indeed help. The decay time was significantly cut and it seems like there was a higher frequency element of the resonance that all but went away.

If the MLV isn't an option, at least I have a few band aids I can try.

knightfly · Post by **knightfly** » Sun Feb 12, 2006 10:48 pm

Dan Fitzpatrick · Post by **Dan Fitzpatrick** » Mon Feb 13, 2006 5:39 am

you could also use opaque material, but don't do complete coverage. i was envisioning dense discs in an appealing or at least regular pattern, covering maybe 30 percent. you'd still be able to see through the glass fairly well. the smaller the "discs" the easier it would be to see through ... just an idea.

Brian Scheffer · Post by **Brian Scheffer** » Tue Feb 14, 2006 12:10 am

Dan, I was thinking of something similar as a fix. I figure that complete coverage will yield a better result, though. It'll be more expensive, but if it'll be more than a band aid, I'd be willing to spend the money.

Brian

Sibirdoug · Post by **Sibirdoug** » Tue Feb 14, 2006 6:17 am

Brian:

I think the MLV curtain idea could help. Thick layers of acrylic or polycarbonate (Plexiglas) sheets or discs with a pressure sensitive adhesive might help as well. This will create what’s called constrained layer damping (CLD) which works well for mids and high frequencies. Unfortunately the lower in frequency the less effective it is. Is there any way you can find the exact frequency of the problem? (an spl meter, CD with test tones and a powered monitor works well)

There is one thing you could try before the others:
I think acoustic resonant modes in your sound booth could be exacerbating the problem. Do you have bass trapping in this booth?