Question about Gobo insulation

Could I use Roxul "Safe N Sound" insulation in place of the Ultra Touch insulation in the gobos? I live in Hamilton, Ontario, Canada and we have the Roxul stuff at the local hardware stores, and it is cheaper than the Ultra Touch.

Hi there, Yeah, I think it would work fine. According to Bob Gold's absorption coeffecient site it has similar effect to the Ultratouch, maybe not quite as much absorbtion in the low end. How thick were you planning on using? I'd use 4" bare minimum inside the gobos, and 6" is even better. The UltraTouch batts I used in the original gobo design are 5.5" thick.... good luck!

I think I will double them up and use 6" in total for each gobo. It comes in packages with 8 pieces of approx. 2 x 4 x 3" so I figure I can make 2 gobos with one package, since I'd have to squeeze 2 batts in for thickness and also for height. Thankfully, its inexpensive (around $30.00 Cdn. for a package). Thanks for the help, JWL!

Yeah, that sounds great. Should work well. Depending on how thick it is inside, you may be able to eliminate the double-H brace, and just have the rockwool sit on top of the sheetrock. In addition, the rockwool is firmer than the cotton, so it may not need the additional support. Good luck, and post pictures! I'm kicking myself that I didn't take more photos of the construction process when I built my 6.

Another thought, remember that in the original design the gobos are 6' high; luckily the cotton compresses really easily and you can get one 8' batt compressed down to 6' without much problem if you work with it. I've never actually worked with rockwool, but somehow I don't think it will compress as easily. You may need to cut the 2x4 panels in half, so you'll have a 2x4 panel and a 2x2 panel, doubled-up.

Yes, that's true. However, I plan on making a couple additional gobos that would be a little taller than 6' (same width though). My ceiling is about 7'10" so I wanted to make a makeshift vocal booth with 3 or 4 gobos in a corner that would almost reach the ceiling for best isolation.

Sounds good. Let us know how they come out.

JWL, in your gobo design, are the screws put in at an angle just for aesthetic purposes?

One other question: I plan a gobo that would be larger than the ones in your design (approx 7' tall and 4' wide) so the weight would also increase. I planned to build a pretty strong base to prevent tipping. I envisioned a row of eight 1x3's (about 20" long) that would be placed 3 inches apart all along the base of the gobo and extending 6 inches on each side. This would give it 8 pairs of "feet". Do you think this would be strong enough to support this monster gobo and prevent it from tipping? Thanks!

I would do 4 evenly spaced feet, but sticking out more like 12" each side and fastened to the base of the gobo with properly drilled pilot holes and screws minimum - better even to use thru-bolts before the insulation goes in, to avoid pull-out. That's pretty tall for such a narrow base... Steve Also, what angled screw holes were you looking at? Didn't see a link or anything - without anything to look at, I'd think maybe pocket hole screws were used??

Steve: I indeed was concerned about the narrow base for such a tall gobo. Do you think there is a better way to make the base more sturdy? As for the screws, I will take your suggestions into account when building. I was planning on building the base seperately and then mounting the body onto the base in such a way so that it would fit between two 4' 2x4s that would be mounted onto the "feet". I will post some drawings tomorrow. I have to get up early tomorrow morning so i can't really do it now. Thanks for your input though! EDIT: Here is the link to JWL's original gobo design: http://www.johnlsayers.com/phpBB2/viewtopic.php?t=5928&start=0&postdays=0&postorder=asc&highlight=

MJP wrote:

JWL, in your gobo design, are the screws put in at an angle just for aesthetic purposes?

Pretty much. I didn't want the screws to show from the outside, so I just "toenailed" them in from the inside. This entire design is pretty spartan overall. Crude but effective, not the prettiest to look at. But they work, and they are affordable. I'm sure with a bit more budget, better carpentry skills, and access to premium tools one could make these look very nice. I don't have any of those 3 at the moment... heh.

Regarding the base: You wouldn't want the legs to stick out 6" either side. Remember, much of the weight is on the side with the MDF and the sheetrock. If it's gonna tip, it's gonna tip that way, so only leave 1" on the cotton side, and put 11" behind the sheetrock side. Note the downside of this design: the gobo must therefore be at least 11" out from the walls. In my use, these are side absorbers when not being used as recording gobos, so I want them flush up against the wall at times. I'm considering a design that would mount under the gobo, and swing around as needed, so when I need to put it against the wall I can swing the legs underneath the gobo so they are out of the way. The weight of the gobo goes back toward the MDF side, so they'll lean right up against the wall. They will not flip forward, the weight prevents it. These will VERY easily tip over in the direction of the heavy side without good legs. I can stand with the MDF side toward me, push the gobo hard in the direction of the cotton, it will swing forward about 2 feet past center and it will then ALWAYS swing back toward center. It's that much of a discrepancy. My current legs are by far the least effective part of this design. Gobo Legs 2.0 are badly needed.

Another note on gobo height: I made them 6' high for 2 specific reasons. First, it opens the room visually... tall people (like me and my singer) can see over them. Second, it allows room for a corner bass trap in the wall/ceiling corners in an 8' tall room. In my room, the gobos go just up to the underside of my corner absorbers.

I also wanted to add wheels, so that's another consideration I'd have to account for. JWL, with your experience with these gobos, how useful have you found them for isolation? I plan to use them as room dividers and I'm hoping to get a decent degree of isolation from one side to the other so I can limit the bleed to the mics on each respective side.

MJP wrote:

JWL, with your experience with these gobos, how useful have you found them for isolation? I plan to use them as room dividers and I'm hoping to get a decent degree of isolation from one side to the other so I can limit the bleed to the mics on each respective side.

These gobos, along with the 6 broadband absorbers I built, changed everything in my recording reality. I'm still trying to figure out my space, but I needed something quick and dirty so I built these. I also put some insulation in the ceiling joists. I have a 15'x17' corner of an unfinished basement, 2 concrete walls and 2 unfinished sheetrock/framing walls with no doors. So really, sonically, the entire basement contributes to the sound. When recording basic tracks, I put the gobos around the drum kit, with the drum kit under one of the insulated spots in the ceiling. I then put the singer outside the unfinished room, on the other side of hte basement, singing into a futon mattress. In the drum overheads, you can just barely make out the vocals, if you seriously crank the gains. I was pleasantly surprised, borderline shocked, on how well they worked for quick and dirty isolation. You won't achieve 100% isolation, but using these gobos and careful mic placement you can get very good results. They also do a great job doubling as side wall absorbers to create a RFZ for mixing in this room.

I wanted to post a bit of my layman's understanding of the theory between these gobos and bass absorption, and ask a question I've been thinking about since shortly after I built the gobos. I want the gobos to absorb as much low end as possible, while recognizing the fact that gobos are not bass traps. In theory, the gobos should absorb all sound at which the wavelength of the sound is smaller than the size of the gobo. The gobo is 2' wide, so IIRC that means everything under about 600Hz-ish will simply diffract around the gobos. However, in a situation with more than one gobo stuck together, it seems that you must account for the total width of the gobos that are together. Observationally, this seems to be true, but I'm not sure about the theory here yet. One thing I've considered; I wonder what would happen if I were to use, say, a 3" holesaw, and cut holes in the sides of the gobos, in the airspace between the cotton and the sheetrock? The air would then be able to pass through and behind the cotton, so it should have a positive effect on the absorbtion. But I'm not sure what that would do to the isolation. If the holes lined up on multiple gobo, would it fully act as one larger absorber?

JWL, it seems like the gobos have really helped you a lot (along with the other treatments). I have no treatment whatsoever yet in my basement, so I am thinking maybe i should build some broadband absorbers first and perhaps some superchunk bass traps in the corners and then the gobos. The main thing for me is that I'd like to use three 4' wide gobos as a kind of room divider. Obviously not soundproof, since they would not be airtight, but still I'd like to get some decent isolation between the two section of the divided room. Thanks for your input JWL!

I just had a thought for the gobos. Making them 7'5" tall would make them huge and a possible tipping hazard. But what if I made a 6' x 4' (similar to your design except 2 feet wider) gobo and then made "mini gobos" for the tops that would be about 2' tall x 4' wide and would rest atop the 6' tall gobos? Then they would be easier to move and take apart. What do you think of this, JWL?

Here is a rough design for a gobo base with wheels (with drawings). 1x3 panels (24" inches long) would be the "feet" of the gobo. I would use 4 of them evenly spaced which would extend 12" out on the MDF/sheetrock side and 4" on the insulation/fabric side. Then I would mount a 4x4 (4 feet long) across the feet at the very base of the gobo (in red in the drawings). This 4x4 would be there so that wheels can be attached on each side of the gobo (4 wheels in total). What do you guys think of this base? WOuld it be strong enough to prevent tipping of a 6' high x 4' wide gobo? Or possibly a 7.5' tall x 4' wide gobo? PS: Drawings are not to scale. EDIT: I just noticed the pictures are HUGE, I thought I had resized them. I have to go to work now so I'll do that when I return. Sorry!

I think that looks good.... except that the wheels are not on the center of gravity. The center of gravity of this design is pretty much right where the MDF/sheetrock is, ie, at the edge of the gobo. So in the bottom drawing, I'd put the wheels out at the edge of the foot slats. I don't think the slats need to extend 4" out the front side. You could attach 2 wheels directly to the bottom of the absorber side of the gobo, and 2 more wheels at the end of the legs. That would probably be more stable. Again, though, the problem for me with a design like this is that it means you won't be able to put the gobos flush up against the wall. Maybe not a problem for you, but that's a deal breaker in my small studio. Regarding gobo size, I'd personally err on the side of modular and stack them however you need to. You might consider some sort of fastening system to lock them together....

Good point about the centre of gravity. I will design some plans based on your advice. Thanks!