Air space vs thin panel between 703 - gobos

[rogerwilco2000]

Hi all, I've gotten much advice from this forum but haven't posted until now.

A few years ago I built a set of rolling gobos/bass traps for my studio space. They are 4' x 6', with four inches of OC 703 and a rear face of 1/8" perforated hardboard (a few are drilled with BAD-style diffusion and one is pegboard). The hardboard offers a "live" side and gives the box frame some rigidity while offering support for the insulation to sit on. They work fairly well for reducing room the sound around instruments (usually a drum kit) and at reducing bleed when tracking multiple people in my live room.

However! I've found I almost never use the "live" side in practice, and I want to rebuild some of my older frames to better accommodate casters. If I do this, I'd like to 1) make both sides absorptive, and 2) keep or improve their effectiveness at reducing bleed and room sound. I don't want to build these massively wider (under 6" is perfect for this space) or add a ton of mass; as-is they are about the limit of weight that I can carry around myself. I also want to keep the same (or better!) level of broadband absorption; the 4" 703 is a pretty nice sweet spot of width and effectiveness.

I'm thinking of either:

- sandwiching the existing hardboard between the two 2" layers of 703
- sandwiching hardboard between the two 2" layers of 703 but drilling larger holes to reduce reflectiveness
- building a 1x3" frame internally to provide a 3/4" air gap between the two layers
- same as above but adding 1/8" hardboard on each end of the frame for additional support

Which one of these approaches do you think would be better? Or is there another I'm overlooking?

[gullfo]

welcome!

since you "almost never" use the live side, maybe start with just sandwiching in-between the 2" 703. on moving the gobos, consider furniture sliders - a pair of 1" on each end and in the middle or on whatever "legs" you're using to stabilize it vertically. inexpensive and easy to replace them, and only a small gap which can be closed with a "sand snake" (plastic tube filled with sand and covered with heavy cloth/burlap/canvas) which forms along the edges and legs to eliminate the air gap.

[rogerwilco2000]

since you "almost never" use the live side, maybe start with just sandwiching in-between the 2" 703

Thanks for the reply. This is the most obvious option to me but what I'm unsure of is how the panel affects absorption. My thought is, since it's not a sealed box, you can't really tune it and it'd be best to drill out as much as possible to reduce mass. On the other hand, maybe the reflection from the panel is more effective?

I've been using this online calculator as a base guideline but it's designed around wall panels, not free-standing gobos, so not really helpful for specifics.

As far as moving them around: I've found, for my uses, sealing the air gap on the floor isn't that important. I've got casters mounted on two 1x4 "skateboards" that attach to the bottom of each gobo with small bolts. The gobos themselves are drilled with threaded inserts for those bolts on the bottom and the side. That way you can unbolt the casters and reattach them, making the gobos horizontal or vertical as you need it. It's pretty nice! The only caveat is it's not super sturdy—I trust it in my studio but wouldn't use it in a commercial place—and it mostly works because my gobos are relatively lightweight. I previously had a set of custom caster plates that rode the gobos super-close to the ground, but they weren't worth the expense.

[gullfo]

the mass is part of what you want to block direct LF and LMF passing though it. larger waves diffract around it regardless but mass preventing the LMF will be a good thing. since it's perforated it will have some particular resonance but since its surrounded by semi-rigid insulation its not much. for those occasions where you do want more life, maybe a thin hard panel with slots cut into it which hang on the front (or back) will restore some reflection and if done with a pattern (e.g. MLS) it can provide some diffusive effects as well.

[rogerwilco2000]

maybe a thin hard panel with slots cut into it which hang on the front (or back) will restore some reflection and if done with a pattern (e.g. MLS) it can provide some diffusive effects as well.

That'll give me what I have already!

Am I understanding that, functionally, in a free-standing gobo, 4" of 703 with an 1/8" perforated panel on one end is more or less equal to a sandwich of 2"/panel/2"?

[DanDan]

https://gearspace.com/board/showpost.ph ... stcount=23

And, to reinforce Glenn's suggestion of sliders...... I had a recording ruined by assuming Gobos in a local megabuck studio would block sound. The gap caused by the rolling stock leaked like hell.

[rogerwilco2000]

https://gearspace.com/board/showpost.ph ... stcount=23

Thanks for this link; I read through it all but I'm not sure I'm putting it all together. I can see the results which suggest a thin membrane facing a block of insulation would have little to no effect. But also that more insulation would have better results. In my case, 4" of 703 followed by an 1/8" perforated panel is working well; my "sandwich" suggestion is only to give the insulation some structure so I can have 703" on both sides. But I still want the effective broadband reduction of the full 4". The way I understand it, higher frequencies would be reflected by the panel and be reabsorbed through the insulation, suggesting a sandwich would be less effective since it's only passing through 4" of insulation total versus 8".

And, to reinforce Glenn's suggestion of sliders...... I had a recording ruined by assuming Gobos in a local megabuck studio would block sound. The gap caused by the rolling stock leaked like hell.

I hear you, but for my uses sealing the air gap on the floor isn't that important; 90% of the time they're used to shape the room sound around a drum kit. I've got casters mounted on two 1x4 "skateboards" that attach to the bottom of each gobo with small bolts. The gobos themselves are drilled with threaded inserts for those bolts on the bottom and the side. If I'm trying to minimize leakage I just unbolt them and lay the gobo direct on the floor.

[DanDan]

Sorry I thought the link to the single post would deliver my point. i.e. Just 1" of fibre blocks much more than I would have thought. So I reckon four inches with or without the hardboard would be quite effective. I think a gobo with the blocker in the middle is a better choice. You don't really want a flat specular reflective surface close to mics or instruments.