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PostPosted: Sun Apr 02, 2006 6:42 pm 
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Note - this thread is now linked from a "sticky" on DIY acoustic treatments - thanks, we'll be looking forward to pix... Steve

I just built 6 of these gobos, and they work very well. I wanted to put the design up for people to see. My objective was to make versatile units that can be used for increased absorption and isolation while recording, as well as being useful for creating a Reflection-Free-Zone while listening/mixing. Gobos are not bass traps, but I wanted these to have as much absorption as possible, and the cotton is a good absorber with a "flat" response through the audio spectrum, down to below 100Hz.

The gobos are 6' tall, 2' wide, and have a reflective side and an absorptive side (ie, they are reversible). They are also very heavy.

Materials for each gobo:

2 - 1x8 pine boards, 8' long
7 - 1x3 pine boards, 22.5" long
1 - 1x3 pine board, 60" long (approx)
2 - 1x3 pine board, 12" long
1 - piece of 3/4" MDF, 24"x72"
1 - piece of 5/8" sheetrock, 22.5"x70.5"
1 - batt Ultratouch acoustic cotton, R19, 24"x94"x5.5"
1 - piece of fabric, such as unbleached muslin, 3'x7'
plenty of drywall screws
silicon caulk
liquid nails or other glue
staples

Procedure:

(Note: all joints are screwed and glued. Predrill your holes, especially the angled holes.)

1. cut each 1x8 into a 6' piece and a 2' piece. Screw and glue them together into a rectangular frame, 2'x6'x8" (yes I know it's really 7.5"... these don't have to be exact as long as it's square). When assembled, lay the unit face down onto a hard floor or a large table. Use the silicon sealant to make sure each joint will be airtight, run a bead along each seam on the inside.

2. Lay the fabric into the frame, and begin rolling the fabric up on the edges, working your way to a 2'x6' size. Staple the fabric, through the folds/rolls, into the inside of the frame, with the fabric on the edge of the frame closest to the floor. Use the canvas-stretching method, begin with a staple on each side at the center, then do the top and bottom, and pull them tight. Use plenty of staples as this has to be strong and tight; as long as you staple through the folds of the fabric it shouldn't rip. Trim the corners nicely, wrap the fabric in place like a birthday present.

3. Once the fabric is firmly attached all the way around, lay the cotton batt into the frame. Work it in so that it compresses into the frame, just up against the fabric. Push it down gently but firmly into the corners so that it looks as tight as possible. Cotton is nowhere near as rigid as 703 or rockwool, so you want to work it into the desired shape.

4. Assemble 3 of the 22.5" side braces, and the 5' brace together into something like a double - H pattern. This is to hold the cotton tight up against the fabric. You want the side braces to screw into the sides of the frame (from the inside, no screws showing from outside. You'll have to screw these in at an angle, predrill the angled holes). The 5' long brace just holds the 3 cross braces together, and holds the cotton in place. You want to push this down as firmly as possible, squeezing the cotton up against the fabric. Cotton compresses a lot, so lean on it. You want the cotton to look as firm as possible over time.

5. measure down the thickness of your sheetrock, and attach the remaining 4 - 1x3 braces to the frame, giving the sheetrock something to attach to. Screw/glue them into place, again predrilling angled holes so no ugly screws show from outside.

6. Lay your sheetrock into place, and screw it in (use glue for the sheetrock, too). Once the sheetrock is in, use your silicon sealant liberally around the edge of the sheetrock, where the sheetrock joins up flush with the outer 1x8s. You should use about a tube of silicon per gobo. Once the silicon is in place, use construction adhesive to liberally coat the inner part of the sheetrock, inside the circle of silicon you just laid down.

7. Lay the MDF board down carefully and precisely so that it compresses the silicon and the construction adhesive. Screw it in only on the outer edges, all the way around.

8. Stand the gobo up, and attach the 2 - 12" 1x3s to the bottom to keep it upright, so that 6" of the leg is even with the gobo (screws go here) and 6" of the leg stick out on the side of the MDF. Most of the mass is in the sheetrock and MDF, so without these legs the gobos will tend to fall over VERY easily.

Note that these are VERY heavy, they are not easy to move alone (I can do it, but I'm 6'4" 300lbs and fairly strong). You may wish to consider adding handles for lifting, or attaching wheels to them.

That's it! You now have a 6' tall, 2' wide gobo with one absorptive and one reflective side. I can say that 6 of these stacked in a semicircle around a listening position or a drum kit makes things sound VERY tight and VERY interesting. They seem to absorb more bass than I expected them to, especially when several of them are placed next to one another.

I hope to upload photographs of these soon, must find my USB cable for my camera.... doh!


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Last edited by jwl on Wed Apr 05, 2006 12:37 pm, edited 1 time in total.

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PostPosted: Mon Apr 03, 2006 3:49 am 
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Note - this thread is now linked from a "sticky" on DIY acoustic treatments - thanks, we'll be looking forward to pix... Steve


Thanks, Knightfly!


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PostPosted: Wed Apr 05, 2006 12:29 pm 
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I found my USB cable, so in the words of the Illustrious Paul W..... PICCIES!

Hmmm, my comments for each shot didn't appear, so I'll explain a bit here.

100_1165 shows 3 gobos and 5 bass traps surrounding a drum kit (actually a 4th gobo is barely visible on the left edge of the picture).

100_1142 shows the inside of a half-completed gobo, with the double-H brace visible. This is to hold the cotton into place, the sheetrock (and the braces that hold the sheetrock) and the outer layer of MDF are not yet installed.

100_1141 shows 2 gobos side-by-side, with a bass trap in the corner. The gobo on the left is the first prototype and does not have the double-H brace installed; you can see the cotton is not as tight as the other units.

100_1140 shows 2 gobos, with a bass trap/broadband absorber between them.

A few final thoughts: these are quite functional units but not terribly attractive. I don't have the budget or the tools for master carpentry work. They could easily be made more attractive with some planing and some fine wood/veneer trim, but honestly I'd rather spend the time doing music.


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PostPosted: Fri Apr 14, 2006 4:16 pm 
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I just wanted to add my experience from recording with these for the first time tonight.

In the past, we recorded all in the same room, lead vocals, acoustic rhythm guitar, bass, and drums. There were no acoustic treatments, and the bleed between the vocal mic and the drum mics was horrible.

After the acoustic treatments (6 of the above gobos, 6 bass traps, and half the ceiling treated with fluffy fiberglass), I stacked the bass traps and gobos around the drum kit. The bass went DI. The guitar went through a pod. And the singer was on the other side of the (far from airtight, door opening with no door in it yet) wall, singing into a futon mattress leaned up against the wall.

The result: ZERO bleed into the drum microphones! Everything but drums is completely inaudible.

This is a fantastic improvement.

Plus, the drums sound a lot better. Much more focused, present, and drum-like. Of course they have new heads, which certainly helps...


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PostPosted: Sat Apr 15, 2006 9:51 am 
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Hey, I built a couple of these and hinged them together, shoving them into a corner to isolate from computer noise and the crappy acoustics of the room. They work great for reducing reflections and decent for reducing the noise from the computer. Coupled with a good preamp, I have a decent vocal setup that doesn't take up a lot of space.

Thanks for the design!

-Lamoni


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PostPosted: Wed Feb 10, 2010 10:21 pm 
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Is thought to be reasonable.

I can't wait for the punchline....

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PostPosted: Thu Feb 11, 2010 1:33 pm 
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Why don't you punch him instead!

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PostPosted: Thu Feb 11, 2010 2:29 pm 
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Looks like John did it already! The post is gone. :)

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PostPosted: Mon May 17, 2010 3:27 pm 
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How can I connect a microphone to my home theater receiver to make announcements? I have a standard home theater receiver and would like to connect a wireless microphone to it so I can use the receiver and speakers instead of using a dedicated PA system or bullhorn.
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PostPosted: Mon Sep 27, 2010 11:11 pm 
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I have same problem? Anyone can explaint it? Please, help me


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PostPosted: Tue Sep 28, 2010 10:59 am 
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you want to make "announcements" over your home theater system? using a wireless mic? did you do a search on the Internet to see if such products were already available or check the home theater forums where its more probable that someone else has already done this? it would be useful to understand your requirements at the very least.

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PostPosted: Mon Nov 11, 2013 9:42 pm 
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Thanks for sharing the DIY Gobo designs. After reading your thread I tried working out on the Gobo designs you have shared, even though I have not reached to the satisfactory models I win achieving some good models. Thanks.


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