Any suggestions on my GOBO design?

bassman · Post by **bassman** » Tue Oct 21, 2003 3:32 pm

I'm getting ready to make some gobos. They are primarily for addressing the acoustics of a small space rather than isolation of instruments, although this is possible as well.

This design stems from one that John has done (search for "gobo" and ye shall find!

) except that these are more vertical for use with vocalists and for treating the mix position while mixing. They have a dead side with 3" fabric covered 703 with an air gap, and a live side using variable spaced 4" slats for a resonating, mid-bass absorber.

Please, any suggestions/modifications would be appreciated as we are slated to build these things on Wednesday the 22nd, weather permitting.

-bassman

PS. I'm building them now and have some pics in a post below.

giles117 · Post by **giles117** » Wed Oct 22, 2003 1:17 am

Remember in your cutting of the wood, you will loose roughly 1/4 to 1/2" of wood for each cut. So on a 96" bd with 3 cuts subtract 1.5 inches minimum for the thickness of the cutting blade and teeth and the wobbling that also occurs.

Bryan Giles

hope that Makes sense.

Also I'd Use Rockwool (SAFB, Mineral Wool) 4" thick instead of the R-19. Much More absorbant than the R-19

Also the 703 usually comes in sheets of 24x48" by the thickness.

DDev · Post by **DDev** » Wed Oct 22, 2003 2:13 am

Actually, with a decent table saw your cuts take out 1/8" each.

Darryl.....

VSpaceBoy · Post by **VSpaceBoy** » Wed Oct 22, 2003 4:37 am

Bassman -

For the Mineral Wool you can get it from United Building Supply at
8975 Empire Connector Dr in Florence.

I got 64sqft of 4" for my gobo's for $17

Good Luck!
Ron

giles117 · Post by **giles117** » Wed Oct 22, 2003 7:10 am

Ron Could you post that info in the builders section with possibly a phone number?

Bryan Giles

VSpaceBoy · Post by **VSpaceBoy** » Wed Oct 22, 2003 10:24 am

Sure thing

bassman · Post by **bassman** » Wed Oct 22, 2003 2:06 pm

Thanks Vspaceboy. er uh, Ron. Nice to have another local here on the case. I will hit that place in the am. I already have the 703. Its actually Johns/Mainville stuff that I bought when I treated my current control room. I think I got 9 bales of 6 panels 2x4 each for $500 total. I still have two bales left, whoo hoo...

-bassman, ashley

giles117 · Post by **giles117** » Wed Oct 22, 2003 10:24 pm

Not to say that it will not have some effectiveness, but what is the density of this stuff. I think I asked someone in another thread to elaborate on which product model # this was so we could verify the specs of the materials.

703 has a density of 3pcf. That is what you are looking for. most fiberglass insul has a density of less than 1pcf. Not good enough.

I made the error of being cheap and took my room apart and re-did it with the right stuff, and whoo hoo. I noticed the difference.

Bryan giles

bassman · Post by **bassman** » Thu Oct 23, 2003 12:39 am

I'll have to check on the specs but it is semi-rigid fiberglass panels. 3pcf, I'll find out...

-ashley

giles117 · Post by **giles117** » Thu Oct 23, 2003 1:13 am

if it i then you will be fine. Just gotta be sure.

Bryan Giles

3pcf is what we are after here.

bassman · Post by **bassman** » Thu Oct 23, 2003 1:57 pm

I just checked out the Johns Manville site:

JM.com[url]

The SpinGlas Board is what I have. I believe I have the 3 pcf version as that is the lowest value you can get from them. The also have 41/4pcf and 6pcf stuff.

the site has absorbtion coefficients in the STC bands listed. They seem very serious about sound control. BTW, this was a far less expensive option than 703.

-bassman

giles117 · Post by **giles117** » Fri Oct 24, 2003 12:54 am

Cool, where did you purchase it? You might want to add this source to the Buildg products forum. Post with a link to the specs.

I am assuming you have the 2" Product

Better yet, here is the link

http://www.jm.com/Insulation/Products/D ... _board.pdf

Bryan Giles

Performance
Type “A” Mounting Sound Absorption Coefficients*
Density Thicknesses Frequency (Hz)
pcf g/cc inches mm 125 _250 500 _1000 2000 4000 NRC**
3 __187 1 ____ 25 0.06 0.26 0.61 0.86_ 0.99 1.03_ .70
3 __187 2 ____ 51 0.17 0.80 1.16 1.15_ 1.11 1.10_ 1.05
02

bassman · Post by **bassman** » Thu Nov 06, 2003 3:31 pm

Thanks for all the suggestions. I'm posting pics of their construction for everyone to see. Thanks to VSpaceboy for the materials hookup. Picked up the wool today.

I have one question. The holes we cut out have been covered with Luon to form a sealed space for the slat resonator. The idea was to make them lighter. However, I think these Luon panels might act as a diaphramatic absorber. They resonate like drums in their current state (no mineral wool, see photos below). Once we get the wool in, shouldn't these tympanic like membranes abosorb the frequencies they resonate at?

-bassman

bassman · Post by **bassman** » Thu Nov 06, 2003 3:34 pm

Here they are back in the basement. You can see the silicon seal around the holes and edges. People kept coming up and asking if we were making speakers, real big ones! Nope, just the opposite.

wildplum · Post by **wildplum** » Thu Nov 06, 2003 10:45 pm

ANyone know where you can get this SpinGlas Board in the San Francisco area?