fiberglass gobos - plywood backing?

  • Thread starter Thread starter FALKEN
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FALKEN

FALKEN

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the title pretty much says it all. I am going to build some gobos for recording my band live in our practice space. without plywood backing, most of the sound will probably go right through, right? we play very loud. I have some 2" fiberglass, and I was planning on making them by stacking 2 panels laying horizontally (creating a 4' x 4' area), putting vertical supports on the ends, and wheels on the bottoms. I am thinking I will probably want a pice of plywood, with a couple 2" panels on each side of it? for those who have experience with this, if you were to do it again, how would you do this?
 
if you were to do it again, how would you do this?
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I would make them 5" deep 4' wide x 6' high. 3/4" Birch ply frames, with 3 layers 1/4" ply backs with 1/8" steel plate on the exterior, CURVED with 72" radius. Line with 4" 703 and fabric covered faces. Add casters and edge latches for fastening multiple units together.

Well, you asked. :D

fitZ
 

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Hey fitZ.............

Doesn't that poor man's arms ever get tired?!?
I've never seen him move his arms from that position. :p ;) :D :rolleyes:
 
I pay him. He's never late, hes consistant, never bitches. Never even takes a break...I like that :D
fitZ
ps, I guess I better draw some others. Inserting this one is so damn easy though.

Actually, after I drew these, I realized I drew them wrong. They SHOULD be a two leaf system for good isolation qualities, but the curved steel plate was an afterthought for one leaf mass. And then again, as far as low frequencies are concerned, they will simply defract around the gobos.
 
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ok how bout a simple design for a guy who can barely use a jigsaw and a drill? I see you don't really care about having absorption on the backside of the gobo. did I mention that there would be a whole band in the rest of that picture? no problem?
 
This is what I did and it worked out great for me.
 

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After looking back at your question, I'm not sure what your using it for. It almost sounds like you are looking for sound proofing from this. Is that the case? (hope not)
 
well, I want to give the drums a drier sound, and also hopefully pick up less of hte band in the overheads and snare mic.
 
Ok, well then it should help. Just make two of what I have shown above and it should work out fine.
 
ok. so I have had 2 suggestions:

1/4" plywood
3/4" plywood. hmmm..


also, do you really think 4" is necessary? the real question though..wont you want to cover the plywood with fiberglass on BOTH sides? so that the plywood side does not reflect more sound into the other instruments; space?
 
Yeah, the 4" seemed a bit thick to me too. I was thinking about making four 2" thick panels similar to the ones in your diagram. I am using 8 psf mineral wool.
 
I went with the thicker to get deeper(ie lower the absorbed fq). Leaving a space behind the insulation and the panel also made it get deeper.
I went with 1/4" instead of 3/4" because of weight. This thing is heavy! Since your not using it to sound proof, there is no need. (IMO)

The reason I didn't put fiberglass on BOTH sides was to have flexibility with the gobo. I didn't want to just kill everything with it. I can use the wood to reflect some sounds to keep it live if needed. Too dead sux. If anything I would make a difuser out of the back. Or maybe a slat panel.
 
4" of RFSB is where it's at.

So is 1/4" ply for the back. You want the back to work like a piston, absorbing sound and reflecting it back into the insulation.
 
ok so I am making these things and now that they are in my hands I am not sure on a couple details...

the panels are exactly 2' x 4'. the wood frame is approx. 3/4" so the total dimensions of the frame are 2' 1.5" x 4' 1.5" . Home de pot sells wood panels 2' x 4' so logically those would have to fit inside the frames. If I get 1/4" thick wood panels, can I secure them into the frame using liquid nails?
 
FALKEN said:
the panels are exactly 2' x 4'. the wood frame is approx. 3/4" so the total dimensions of the frame are 2' 1.5" x 4' 1.5" . Home de pot sells wood panels 2' x 4' so logically those would have to fit inside the frames. If I get 1/4" thick wood panels, can I secure them into the frame using liquid nails?
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What are you reffering to when you say the panels are exactly 2' x 4' (the first time) You mean the insulation?

To answer your question, liquid nails would prob do the just but I would still use some brads or screws or something as a back up.
 
Well then I would mount the frame inside the wood panels making the outer demention 2'x4'. Its better to "squeeze" the insulation in the space than have it loose.
 
nah..I don't think it will be loose. I made some wall panels and they're tight. I just dont think my skills are apt enough to put a nail through a 1/4" piece of wood...was wondering about the liquid nails. also - is the air space necessary?
 
I just dont think my skills are apt enough to put a nail through a 1/4" piece of wood...was wondering about the liquid nails. also - is the air space necessary?
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There are a dozen ways to do this. Falken, get yourself a few 3/4" x 1 1/2" pieces of wood from HD, cut them to fit as a "spacer". Nail or screw the plywood on to the strips as shown, not vice versa. This will give an airgap, which is not required, but will lower the bandwidth of absorption a bit. Plus, it gives you an edge to fasten the frame to. Make a pillow case for the fiberglass or wrap it and pull the fabric tight from the backside. Trim it to leave a gap of 1" and secure it with thread by stitching from side to side, top to bottom. You only need a few of these threads to keep it tight. Nail or screw the framework to the 3/4"x1 1/2" cleat, insert the fabric covered fiberglass, nail through the frame into the fiberglass to hold it in the frame or use velcro. VOILA!!

However, gobos are supposed to inhibit the propagation of sound in a defined area, and to do so requires mass. Most gobos are built with much heavier material than 1/4" ply. I've seen plans for large ones that used TWO layers of 3/4" thick material such as MDF or ply. Even 2 layers of drywall constrained between 2 layers of 1/4" MDF or ply. All these layers are GLUED togeather as well as screwed to a frame. The glue dampens the panels. Since these panels are very heavy, they are usually mounted on wheels for mobility Of course, since gobos only serve to somewhat isolate mid and high frequencies, as low frequency wavelengths simply diffract around them, mic placement and distance are your friend when using gobos to isolate one instrument from another.
fitZ
 

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I would have to re-buy a lot of material to do that. I have already decided on my design..I just do not have the construction know how to know if the liquid nails will hold the wood in place.
 
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