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DIY Gobos

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stainless:
   Where the word came from I have no idea, but Gobos are quite useful in the studio when you need to isolate or “contain” sound, such as an amplifier, drums, etc.  There have been various approaches taken by the do-it-yourselfer, ranging from a blanket covering a sawhorse, to old closet doors, office partitions, and more elaborate and permanent designs.  Does the blanket design work? Sorta- it does depend on how heavy the blanket is, and what its draped/hung over.  Some designs have one side of a solid material construction, while others are simply a panel of some sound absorbent media. 

   I recently replaced the carpeting in my studio with bamboo flooring. It is much less of a housekeeping concern, looks better (IMHO) and makes the room so much more alive!  The drums became especially hot and bleed during efforts to record “live” had become a concern.  I had used gobos in a rehearsal space years ago, which helped greatly to keep volume assault from overtaking the sound system.  They were crude, made from old closet doors cut in half and covered with carpet.  The carpeting was used to make a ‘hinge of sorts’  so the gobs could be set up like you’d open a book and stand on edge, and they were pretty stable… but when we didn’t want to use them they didn’t store so well… and after a few beers got spilled on them they didn’t smell so great either…. We proclaimed the “death of the Gobo’s) and unceremoniously snuck them into a dumpster!

   The hinged idea was appealing for the drums as I would be able to have an angled partition so that any sound reflected back at the drums would not be from a parallel surface. And with a little thought, the hinged panels could fold flat for easier storage.  I like pine, both for it’s appearance and relatively low cost, but any type of wood could be used, including plywood or MDF.

   If you’re a DIY-er at even the most beginning of levels  you  will probably have (or have access to) the necessary tools. My “workshop” is out on the patio. I do have a portable table saw, but an orbital saw, or even a hand saw (if you’ve got a good eye) would work.  Some white/yellow wood glue, some 6d or 8 d finish nails, spray adhesive, some amount of baric large enough to cover you gobo (one or both sides).  I use a shoulder joint (see fig 1.) for the corners of the frame. It’s easy to make and results in a stronger frame. I cut mine ¼” in depth the width of the pine lumber (in this case ¾”).  This is not an absolute ”if you don’t do this you’ll burn in hell along with your weak puny excuse for a gobo…”  As long as you get square cuts, a butt joint would also work.  I use the shoulder joints on the top and bottom pieces of the frame, so the overall length of the top and bottom pies is 1 ½” longer than the inside of the frame.  To allow for the shoulder joints the sides are ½” long than the inside dimension.  I opted to use the rigid fiberglass (RFG) panel right out of the carton- so the inside dimension of my frames are 24” x 48”, which translates into top/bottom pieces being 25 ½”, and side 48 ½” .  I used 1 x 4 pine lumber, but you can use whatever size material you want, depending on how much sound absorbing media you want to fit “inside” of the frame. 

   The frame is glued and nailed together and I glued /nailed some cross pieces flush with one edge at each end and in the middle. You could add more, to the point of building something akin to a Heimholtz Resonator, or make one side solid . The frames are set aside to dry and I now cut some ¼” perforated hardboard (aka peg-board) to fit inside the frame (in this case 24” x 48”. (see fig 2.) I spray some adhesive on one side and layup some fabric. I find it a good idea to iron the fabric (unless you’re into the wrinkled look) This is more for aesthetics so you could leave the fabric off if you wanted, but it seems (to me) that it helps to eliminate places for dust to collect!  I  set these aside to dry.

   Now I take one of my RFG, which this time is a Knauff product, 2” thick, and aside from the black color on one side it has about the same weight as the Dow 703 or the Certainteed CB300.  RFG was originally/ mainly used as thermal insulation on ductwork, which is why many places will not sell to you unless you have a HVAC license!  If I had to cut the RFG down in size an electric carving knife works great and gives a nice clean cut, but as my gobo is built for full panel, all I need to do is cover one side with fabric, which again is glued using the spray adhesive (see fig. 3).

   Now that the frames have had time to dry I router the edges and sand smooth. I left mine unfinished, if you want to seal or paint, now would be the time to do it!  The ¼” perf board is placed inside the frame with the fabric towards the outside, and pushed all the way in until it’s up against the cross-pieces.  A couple of staples  is all that’s needed to keep this from moving. The RGF panel should fit snuggly into the frame,  so push it in  (fabric side out) using a wide blade putty knife if the fabric starts to lag behind (see fig. 4). 

   Now I set the 2 gobo panels next to each other with the perf board sides facing each other. I lay the hinges on the upper edge (see fig. 5)  and using a self-centering punch mark the screw holes.  The hinges are screwed in place and some felt “feet” are placed on the floor edge of the gobo (so as not to scratch the floors).  You’re done, except for cleaning up any mess you’ve made!

   Go make some music!

stainless:




There is no right/wrong way of building a Gobo: how big/small/fat/thin all depends on your specific needs.  Have fun!

RawDepth:
Cool! Nice job. Thanks for the instruction.

I really want to make some of these. I am saving up to order the material. I am thinking of using the stiff mineral wool.

http://www.atsacoustics.com/item--Roxul-Rockboard-60-Case-of-6--RB60.html

I may use double layers to make the gobos 4" thick overall. Also I may forgo the pegboard because I believe it will cause direct reflection back to the mics. I want mine for recording a single instrument in a room by itself. I just want to better control room modes, wall reflections, and such.

stainless:
pegboard is not very dense and with the holes it's more of a diffusser, and in my case, I wanted some of the sound reflected back- it also solved how to cleanly cover with fabric on both sides, and with the mic on the one side if the gobo, the pegboard protects the RGF from getting dented if it gets pushed into the mic (not tat that is a critical concern)

I'd thought about making them 4", and I suppose if I need too it I can cover another piece and place velcro on the corners and middle/side , but I don't think it will be necessary

I'll know tomorrow night ???

when i need to record the amp by itself the gobo moves to the side

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