Gobos with 6" thick of acoustic foam...deaden highs too much?

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RecordingMaster

RecordingMaster

A Sarcastic Statement
Hey all!

I have some old acoustic foam sheets that are 3" thick and each 2'x4'. They are useless as I now have all broadband and bass traps using OC703. They are the old school king with the pill shapes on it. It looks like this but is yellowed. http://www.proaudio.com/images/sonex_classic_charcoal.jpg

Anyways, I was thinking I would stack them together side by side and then another layer on top of each other so they are 4'x4' and 6" thick. I would place them in a wood frame, cover in burlap fabric and add some feet so they stand upright. I have enough to make two of these. I would use these when wanting more "focused" sounding drum tracks without as much room tone, or to isolate two different instruments being recorded in the same room at the same time, or to put on either side of an electric guitar cabinet or behind acoustic guitar player while tracking to reduce some room tone as well. When not in use, I figure I could place them straddled in two of the room corners in front of my corner bass traps, to just absorb even more low end in the room while mixing, etc.

My only worry is, will this just deaden out all the high end too much on the source I am recording? I know thin foam does nothing other than reduce high end. But when going 6" thick, I am assuming (hoping) it evens out the spectrum a little bit? Where as I am absorbing more of the frequency range so it doesn't sound too much of one thing (ie too dead, too boomy, muddy, etc). I was thinking of putting a wood front and back on these and cutting various large holes, but then I'd worry this "gobo" will now have a reflective portion that may reflect back into the mic, making it sound as if I had the source right near a wall or hard surface and defeat the whole purpose.

What do the acoustics guys think?

Thanks in advance for the help!
 

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If you find that there is too much top end loss, you could just cover part of the foam with a thin sheet of ply wood or something similar. The other way is to put a solid surface on one side and the foam on the other so if the situation is too dead turn the gobo around.

Funny, I googled gobo design and found this interesting page http://lib.store.yahoo.net/lib/mercenary-audio/abbey.pdf

Alan.
 
RecordingMaster said:
...Anyways, I was thinking I would stack them together side by side and then another layer on top of each other so they are 4'x4' and 6" thick. I would place them in a wood frame, cover in burlap fabric and add some feet so they stand upright. I have enough to make two of these. I would use these when wanting more "focused" sounding drum tracks without as much room tone, or to isolate two different instruments being recorded in the same room at the same time, or to put on either side of an electric guitar cabinet or behind acoustic guitar player while tracking to reduce some room tone as well. When not in use, I figure I could place them straddled in two of the room corners in front of my corner bass traps, to just absorb even more low end in the room while mixing, etc.

My only worry is, will this just deaden out all the high end too much on the source I am recording? I know thin foam does nothing other than reduce high end. But when going 6" thick, I am assuming (hoping) it evens out the spectrum a little bit? Where as I am absorbing more of the frequency range so it doesn't sound too much of one thing (ie too dead, too boomy, muddy, etc). I was thinking of putting a wood front and back on these and cutting various large holes, but then I'd worry this "gobo" will now have a reflective portion that may reflect back into the mic, making it sound as if I had the source right near a wall or hard surface and defeat the whole purpose.!
Click to expand...
I think it should work out fine. 3" deep both sides, 2" one, four on the other or what have you. You'd just be aware a deeper side just absorbs lower.
By the same token spreading out a lot of 1" stuff is a lot of surface effectively cutting just highs.
Stacking' it is a lot less surface -but it goes deeper (well lower :)
 
That page IS pretty interesting, Witz! Although I won't be building something that elaborate. Also, as I mentioned, I wouldn't want a hard surface on one side because in my mind that sort of defeats their purpose (for what I want to use them for anyways eg: putting around a source to dry out the ambiance going into the mic, like an amp). I always worry about having a hard surface on one side because wouldn't reflections bounce off of it and into mic and create some sort of anomaly at times?

Mixsit, both traps I am thinking of making would be exact copies of eachother. Both 4'x4' and 6" thick of acoustic foam, free-standing, covered in fabric. But yeah, 1-2" foam all over the walls in a room would really rob high end, but I am not treating a room, I am temporarily treating around an object to isolate and focus it. So I'd worry that if I put these things around said "object" (like an amp or drums) I would be robbing the high end from the direct source.

I wonder...

Anyone else care to chime in?
 
RecordingMaster said:
... Mixsit, both traps I am thinking of making would be exact copies of eachother. Both 4'x4' and 6" thick of acoustic foam, free-standing, covered in fabric. But yeah, 1-2" foam all over the walls in a room would really rob high end, but I am not treating a room, I am temporarily treating around an object to isolate and focus it. So I'd worry that if I put these things around said "object" (like an amp or drums) I would be robbing the high end from the direct source. ..
Click to expand...
Well that was the point. You are not treating the room.
And the gobo.. well they're not in line with the the sources or something.. it's preventing bleed / allowing some isolation / tightening up the sound from the source -a really nice set of variables to have there.
If what you seem to be confusing here is if to have some movable' difusion pannels or what have you to add ambience or reflection effects, would be from a different thing all together.
Put another way.. all they're taking away is the stuff that's already bouncing around in the room.
 
RecordingMaster,

Those would make great gobos to do what you had in mind. The inclusion of a 1/4" thick plywood panel in the MIDDLE of the gobo would cause the gobo to work better at isolation almost down to the transition region of your room. Adding a hard panel BEHIND the foam should not cause any reflection problems.

Cheers,
John
 
Thanks for the input, fellas. I ended up just making them the way I described, mostly out of impulse to get them done! Here is a picture of one completed. I was thinking of putting some wheels but then that would make them higher off the ground and more of an open gap across bottom edge. Great way to make use of some old crappy foam that is falling apart. It still absorbs!

untitled.webp
 
Thanks again!

And we shall see mixsit! The more research I did, the more I realized that it just is what it is. Gobos for isolating and drying out a certyain source are going to be absorptive and there's no way around it. The thicker, the better so these should be ok! :D

Here they are completed. You can see some of the bass traps and broadband panels I am working on in the back there as well. gobos.webp

And while I'm at it, here is a pic of some desktop racks/speaker monitor stands I just built as well. Going to stain them the same colour as the enclosure I made for my 2 BCF2000's. racks.webp

The BCF enclosure from afar (old pic)...Desk.webp
 
Nice work, did you use 1"x6" wood? I want to do the same thing with 4" traps, and want to keep them at 3'6" high so I can put one on top of the other for gobo work, when not in the room corners. Trying to figure out an easy way to keep them secure when stacked - the little "feet" you made are good on the floor, but not when stacked.
 
mjbphotos said:
Nice work, did you use 1"x6" wood? I want to do the same thing with 4" traps, and want to keep them at 3'6" high so I can put one on top of the other for gobo work, when not in the room corners. Trying to figure out an easy way to keep them secure when stacked - the little "feet" you made are good on the floor, but not when stacked.
Click to expand...

Yep, 1x6 wood. 2 Angle brackets inside each corner for reinforcement and a big ol 2x4 down the Center for extra reinforcement (you can kinda see it through the fabric). Feet are just 2x4's and stacking shouldn't be a huge issue if I flipped the other one upside down, however I would recommend in that case that you have the wood frame exposed somehow so they stack better (instead of fabric in fabric).
 
If you put two/four studs on the top of one, holes to match on the top of the other, when you flip, they would be sturdier.
 
Mount them on these! lol
 

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