Building 703 GOBOs

[R_Spaulding]

I am going to build some 4ft x 4ft gobo walls primarily to be placed around the mic stand for vocals (and drums too when I need them). I'm using 2" thick OC 703 material inside a wooden frame on an adjustable stand. Should I put a wood backing on the back side of these walls or just leave it open on the both sides?

 

[mixmkr]

My first thought is you're trying to control bleed from outside sources (or containing the drums) by using these gobos. At least, that is generally the purpose for them. Therefore, I'd consider extra thickness over the 2" and I would put the wood backing on them too. I think the more mass, in general, is best for sound transmission loss.

I'll step back and be ready to be corrected

One other thought too.. 4' high around a vocal mic isn't going to do much, as I'd suspect the mic will be higher than the gobo, if the singer is standing.

Also, don't forget the height of the cymbals on the drum being above the gobos either. If line of sight isn't too important, I might make them taller for these reasons.

I think the SMALLER gobos are handy for helping isolation on guitar amps, stuff like that.

 

[R_Spaulding]

okay, let me rephrase...

I bought SIX 2'x4'x2" thick pieces of OC 703 and I want to position them around a mic stand to as a make-shift vocal booth. What would be the best way to use the 703 for this purpose?

 

[mixmkr]

I don't think you'll get a "booth" with that small amount, but maybe you can get three 2x4 x 4" "gobos" on stands that you can make "3 walls" around the mic.

Personally, I'm not sure I'd go to the trouble and try and make what you're thinking you might need. Instead, I might mount them on the wall in a more useful manner, that might benefit things in other ways also... but when singing, have the singer face into the mounted 703 with the mic between the singer and the wall mounted 703 panels.

 

[R_Spaulding]

is it better to have 4" thick than 2" thick panels?

 

[suprstar]

is it better to have 4" thick than 2" thick panels?

I think more 703 is always gonna be better. I'm also going to be building a couple 703 gobos in the near future, and I have the same questions about the wood backing. It would probably give you more isolation, but I'm afraid it would also give more reflections as well..

I've also been kicking this idea around: Use a sheet of plywood for a backing, put a 2" layer of 705 on it, then a 2" layer or 703 on top of that. Any merit to that?

 

[RICK FITZPATRICK]

Should I put a wood backing on the back side of these walls or just leave it open on the both sides?

First off, even though 703 absorbs sound very well, it only does so if there is a boundary behind it. With no boundary, sound transmits right through it. It has no Transmission Loss qualities on its own.

Second, even though gobos help with isolating one instrument from the other to a degree, they only do so if high enough and wide enough to keep higher frequencies from flanking around them. Thats why it usually takes multiple gobos to isolate an instrument or vocalist from others. However,they do almost nothing for Low frequencies, as the wavelengths are longer than most small rooms, and simply flank around the gobos. However, they can only perform their duty if there is a MASS boundary, which in the case of a simple frame, has NONE. Therefore, what would be the point of a frame lined with 703 in the middle of a room, especially if they are only 4' high? They would niether absorb or help isolate.

 

[mixmkr]

Therefore, what would be the point of a frame lined with 703 in the middle of a room, especially if they are only 4' high?

Even though I agree with your entire post, OC 703 panels are the "lava lamp" of 2009... ya didn't know that?....or am I just catching up

 

[pandamonk]

First off, even though 703 absorbs sound very well, it only does so if there is a boundary behind it. With no boundary, sound transmits right through it...
...Therefore, what would be the point of a frame lined with 703 in the middle of a room, especially if they are only 4' high? They would niether absorb or help isolate.

Is that true?

One experiment, if no-one is around of course, is to put a duvet over your head, stand in the middle of a room and talk. Even though you are as far as possible from boundaries, and the duvet isn't the best absorber, your voice still sounds pretty dead. I find the same happens with gobos without a mass boundary, although the effect is reduced somewhat (and my rooms are small).

Increasing the distance from a boundary increases absorption at lower frequencies but reduces at higher frequencies. This is what I've always found/been told. Wouldn't a 4" gobo 12" from a boundary start to work like a 16" panel at lower frequencies, ie. it would theoretically absorb well to around 200Hz then start tailing off (instead of 850Hz flat against a boundary)? Although, it would start tailing off at higher frequencies also?

So a 2" gobo panel 3' from a wall should absorb well to around 90Hz, but would tail off quite significantly at higher frequencises? Obviously the thicker the material the better it will absorb.

Is my understanding correct or am I way off?

Also R_Spaulding said he would mount them on adjustable stands.

 

[RICK FITZPATRICK]

Is that true?

Hello pandamonk. Well, lets look at what he said.

I am going to build some 4ft x 4ft gobo walls primarily to be placed around the mic stand for vocals (and drums too when I need them).

In the context of GOBO's, yes, I believe I am correct. Gobos are used for 2 reasons. For isolation, and for absorption/reflection. In the context of isolating a mic from other sonic sources, YES, mass, especially with dimensions to keep sound from flanking, must be involved or sound from other sources will simply transmit through the fiberglass. Your experiment should directly prove this. Put a blanket over your head. Yes, the sound WITHIN will be deadened. However, place a radio nearby and listen. Now, put a plywood box over your head and listen to the difference..

 

[RICK FITZPATRICK]

OC 703 panels are the "lava lamp" of 2009... ya didn't know that?....

In the middle of a room? With no back panel? Hmmm, at least lava lamps put out light and look cool. What would these panels do besides take up space.... They won't absorb, and they won't isolate anything, so whats the point? If this has become some kind of fad, just to look quasi cool....I guess I'm the one thats behind the times. But geeezus...what a waste.

 

[stevieb]

703 Gobos? Why do you need so many?

 

[mixmkr]

In the middle of a room? With no back panel? Hmmm, at least lava lamps put out light and look cool. What would these panels do besides take up space.... They won't absorb, and they won't isolate anything, so whats the point? If this has become some kind of fad, just to look quasi cool....I guess I'm the one thats behind the times. But geeezus...what a waste.

yeah...I agree... I was joking. It's the "foam by mail" that I meant was the "new" lava lamp"!

 

[Slowjett]

It sounds like he is talking about sound absorption, but isnt a gobo a way of shooting light on a wall? What the hell is a gobo in this sense?

 

[suprstar]

A gobo is a 'go-between', a portable wall placed between or around a sound source you're recording, to help isolate and absorb sound. If you're tracking 2 instruments in a room, you can help prevent sound from one source bleeding into the other instrument's mic.

My question above still stands, would a gobo with a plywood backing, 2" of 705 on the plywood, then 2" of 703 on the 705 be better than plywood + 4" of 703? I thought the 705 might be better at absorbing some lower freq's, but I think it's more reflective of the high freq's too, so 703 on top of it might be a good idea. On a plywood backing, how much better would 4" of 705+703 or 703+703 be than just 2" of 703? The difference will be a few hundred bucks for the gobos I'm thinking of building.

 

[RICK FITZPATRICK]

My question above still stands, would a gobo with a plywood backing, 2" of 705 on the plywood, then 2" of 703 on the 705 be better than plywood + 4" of 703? I thought the 705 might be better at absorbing some lower freq's,

It probably would, if placed where it does the most good....ie...the corners of the room. However, without testing this in a lab, theres really no way to GAURANTEE the performance. Its all opinion.
So, heres my opinion. Look at it this way. To really absorb low frequencies, the treatment must be placed where the low frequency modes terminate...ie. the corners of the room. It makes no sense to place bass traps in the mddle of the room...ie...gobos as bass traps, although they will provide some low frequency absorpton, but not modal(from my understanding of modal absorption) I beleve you can verify this here:
http://forum.studiotips.com/viewforum.php?f=8
Hence, my suggestion is just use 2" or 4" 703 and be done with it.
The point of gobos is:
1. Placing a boundary between instruments to prevent bleedthrough. This means a boundary wide enough(2-4' is good) and high enough(6-7') to prevent high frequency flanking around and over. Two or three units around a vocalist or drummer should suffice depending on the micing situation. These will not prevent low frequency flanking, however they can attenuate them.

2. To prevent reflection back into the mic. The deeper the pile, the better it will absorb low mid frequency reflection. You can also make them diffusive on one face instead of specular, via well(QRD) type construction.
There are lots of ways to configure gobos, and even make the stackable. You can even make a gobo with one side with absorption, and the opposite side diffusive, and even alternate them Like this....

You can make them half this height and stack them as well. Wheels help as well, but need an offset bracket to allow the gobo to come close to the floor.
Also, you can make both sides absorbant, but place spaced slats over the fiberglass on one face, such as John Sayers design

The middle panel should be fairly massive, such as 3/4"MDF or a layer of plywood and gypsum bd(drywall) or even cement board over a layer of another substrate such as 1/2" mdf. It all depends on availabilty of materials, you skill set, tools, budget, etc. There are many ways to do it. But the end result should be aimed at placing a sizable mass between instruments.

fitZ

 

[pandamonk]

Is that true?

Hello pandamonk. Well, lets look at what he said.

In the context of GOBO's, yes, I believe I am correct. Gobos are used for 2 reasons. For isolation, and for absorption/reflection. In the context of isolating a mic from other sonic sources, YES, mass, especially with dimensions to keep sound from flanking, must be involved or sound from other sources will simply transmit through the fiberglass. Your experiment should directly prove this. Put a blanket over your head. Yes, the sound WITHIN will be deadened. However, place a radio nearby and listen. Now, put a plywood box over your head and listen to the difference..

Aww FitZ, I thought you would have known by now that I was talking about absorption, especially since my whole response was absorption based. I simply left "or help isolate" in the quote.