Gobo / Baffle Plans

[Seamus TM]

I need to build some quick/easy/cheap/effective gobos for the live room.

Does anyone see why this plan wouldn't work?

They are 4'x4'.
I'll have them so they I can hinge two together so they can be situated in a "V" formation for stability.

Pegboard side will have 3" behind it, so they could absorb around 400Hz-500Hz as well as reflect highs.

Alternatively, I could have the absorptive side have 2", instead of 3", of rockwool. That would allow me to have 4" behind the pegboard. That would absorb more like 300Hz, which may be more useful.

Thanks,
Seamus

[SAC]

Assuming that you have done the calcs for a perforated absorber and that you want a flat (as opposed to a curved surface) providing hard focused reflections, why do you have the solid center divider?

And not to cause trouble, but why do you not simply use one side as an absorber and the other side as a PRD for real diffusion with the added benefit of lacking the on axis perpendicular (normal) lobe?

[Seamus TM]

Hey SAC.
How've you been?

Well, the solid center is for (most importantly) the isolation purpose of the gobo and, also, to be able to create the sealed cavity for the pegboard side.

I considered having one side be a poly.
Assuming a 6" depth of the poly, that would leave less than an inch of rockwool for the absorptive side. I want to try and keep the total thickness at 7.5" (using 1x8 pine).
A QRD is just too much for me to get into for these.

These are for baffling off guitar amps in the live room, btw.
We have a 44' x 14' live room.

[SAC]

For isolating guitar amps I might just suggest as thick an absorber as possible.

I can't see any real benefit in creating multipath reflections and phasing issues from the amp with a reflective side.

I am assuming that any recoding of the amp will be some combination of DI and close micing. Just like with vocals, you wouldn't want additional reflections effecting the close micing.

...my $.02

[Seamus TM]

I was planning on having the absorptive side facing the amp and the reflective side facing the room.

Are you saying that I should just make them with both sides absorptive?

[Seamus TM]

No, there wouldn't be any DI guitar happening.

These are just for those times when we have drums and guitars going on at the same time during tracking.
Sometimes, we just want a little less amp going on in the room without having to turn the volume down.

[SAC]

Yes. I would just allow it to be 'one large absorber'.

You only need a hard surface if you are planning to 'tune' the absorber, and I really don't see the need. And I don't really see any benefit for a diffusor in this role (as much as I like diffusion!)

I am assuming that you simply want to help control the effective dispersion of the sound and the gain can be controlled with the little knob they put on the amp itself.

Is there more?

[SAC]

I can't help but think of the SansAmp for exactly these purposes - obtaining the precise tone and character without having to blast an amp into overdrive.

Unfortunately. putting absorption all around the amp will change the sonic character dramatically.

Coming from a sound guy perspective, I can't help but add what so often caused all sorts of frustration to the musicians - that turning down the volume does more to contribute to a quality sound then any amount of high volume overdrive ever did!

(And if the guys need that visceral impact - get a bass shaker and attach it to a stool. That by the way works incredibly well for the thrones of the now deaf drummers! Seriously! Especially as many are turning up due to the volume of the drums - which could also benefit from Plexiglas iso panels or simply absorbers )

But now, having gone and suggested volume control, I suspect I have over stayed my welcome....

[Seamus TM]

Right on.
I guess that I assumed that even if I had two absorptive sides, there would need to be some level of mass in the middle to maximize it's isolating properties.
Hence the 1/2" MDF.
No?

[Seamus TM]

Originally Posted by SAC

I can't help but think of the SansAmp for exactly these purposes - obtaining the precise tone and character without having to blast an amp into overdrive.

Unfortunately. putting absorption all around the amp will change the sonic character dramatically.

Coming from a sound guy perspective, I can't help but add what so often caused all sorts of frustration to the musicians - that turning down the volume does more to contribute to a quality sound then any amount of high volume overdrive ever did!

Ah, well, we tend to use a lot of low wattage tube amps at our place.
I'm not looking for total isolation, by any means. We have a couple of iso rooms for that... or I should say room that we use for iso, actually.
This is just for those times that the band "needs" to all be in the same room with everyone and everything going on at once. Just to gain a little more control as to the level of guitar that ends up in the overheads.

[SAC]

You don't need two 'isolated' sides. One 'facing the amp' should do fine.

[Seamus TM]

I'm sorry, man, but I'm a little confused, I think.

What I am trying to do is make a 4' x4' baffle to place in front of an amp to reduce it's volume in the room... or to place around a kick drum to reduce amps from getting into the outside kick mic... etc.

Forgetting the pegboard for a minute, one plan would be 2 absorbers with a sheet of MDF in the middle.
It's my understanding that this would effectively create a barrier between two sound sources.

Now, what I think you are saying is that I don't need the MDF? Just a 8" thick slab of rockwool would be just as effective?

[SAC]

I interpreted your meaning to be that you were interested in 'isolating a guitar amp' while leaving a "reflective side facing the room."

Now you effectively want two absorbers to isolate both drums and a guitar amp...

You sure make life hard!

Since this is being done solely with porous absorption, my gut says that it will be most effective without a hard barrier as this will maximize the amount of material to reduce the gain by dissipating the maximal velocity as friction.

And a hard barrier will be essentially useless for low frequencies and the highs will be better mitigated by the increased absorptive material rather than the reflection - although those frequencies reflected by a hard membrane would effectively traverse the absorptive material twice but at a much lower velocity - thus reducing the effectiveness of the available absorptive material!! (Gee, and at an increasing incident angle, the amount of absorptive material traversed will increase, but then, so will the amount of energy simply reflected increase as well...so many variables!)

My guess is that absorption will be more effective at the higher energy lower mid frequencies than that with a hard surface that will reflect the higher frequencies that possess lower energy and smaller wavelengths that are more easily addressed anyway. So I will error on a thicker absorber that is a bit more effective with the lower frequencies.

dd or Ethan or Jeff or Glenn or Andrei or ... have you guys done any tests on absorbers placed between objects to determine the most effective config?

[riffster]

I have built some gobos very similar to yours and they work pretty well at minimizing mic bleed. 4" insul -> 1/2" MDF <- 4" insul

[Seamus TM]

Originally Posted by SAC

I interpreted your meaning to be that you were interested in 'isolating a guitar amp' while leaving a "reflective side facing the room."

That is my original thought, yes.

Originally Posted by SAC

Now you effectively want two absorbers to isolate both drums and a guitar amp...

I'm not sure where you get the two absorber thing.
I just want to build some gobos. You know, the things that you use in live rooms to minimize bleed. Sometimes they have one absorber side and one reflective side. Sometimes they don't.

Originally Posted by SAC

You sure make life hard!

... I know. I want them cheap and easy, too.

Originally Posted by SAC

Since this is being done solely with porous absorption, my gut says that it will be most effective without a hard barrier as this will maximize the amount of material to reduce the gain by dissipating the maximal velocity as friction.

And a hard barrier will be essentially useless for low frequencies and the highs will be better mitigated by the increased absorptive material rather than the reflection - although those frequencies reflected by a hard membrane would effectively traverse the absorptive material twice but at a much lower velocity - thus reducing the effectiveness of the available absorptive material!!

My guess is that absorption will be more effective at the higher energy lower mid frequencies than that with a hard surface that will reflect the higher frequencies that possess lower energy and smaller wavelengths that are more easily addressed anyway. So I will error on a thicker absorber that is a bit more effective with the lower frequencies.

dd or Ethan or Jeff or Glenn or Andrei or ... have you guys done any tests on absorbers placed between objects to determine the most effective config?

I'm pretty sure that they would need some level of mass to be really effective, but I am wrong more often than I am right.
Think about standing in front of a wall made entirely of 8" of fiberglass with an amp on the other side.
Do you hear it?
Now think about standing in front of a wall with a sheet of plywood or mdf or sheetrock or whatever added to the fiberglass...
Do you hear it less?

This doesn't take into account that I'm not talking about a whole wall, but just a 4' x 4' section. The biggest difference there would be the diffraction of sound around the 4' x 4' section.
I do think, however, that the principle remains true.

It's just isolation vs. "treatment", right?
Kind of two different things.
I understand that by putting these gobos in the room will change the sound of the room somewhat, but that's ok.

[Seamus TM]

Originally Posted by riffster

I have built some gobos very similar to yours and they work pretty well at minimizing mic bleed. 4" insul -> 1/2" MDF <- 4" insul

Nice.
That's pretty much exactly what I'm talking about.
Maybe I'm not explaining the purpose well.
If that's the case, I apologize to SAC.
...and, as always, thanks for putting in so much effort, SAC.
thumbsup

[SAC]

Hahaha!

I think we agree ! I referred to 'two absorbers' as the one with a hard partition that effectively made it into 2 absorbers 'back to back'. Sorry for any confusion.

And the example posted is exactly what I think would work just fine. A 'single' thicker absorber effective from either side.

...As long as you don't get any of that 'directional' absorptive material!
I had some of that directional wire once until the electrons became confused and nearly ruined my stereo. Now I avoid it until I can find some smarter 'edumaketed' electrons.

[iriegeorge]

Your images are very similiar to gobo's that I have, with the exception that on the absorbative side we left is thicker and split that side with a wood strip and gave it a convexed shape.

[Seamus TM]

Originally Posted by SAC

Hahaha!

I think we agree ! I referred to 'two absorbers' as the one with a hard partition that effectively made it into 2 absorbers 'back to back'. Sorry for any confusion.

And the example posted is exactly what I think would work just fine. A 'single' thicker absorber effective from either side.

...As long as you don't get any of that 'directional' absorptive material!
I had some of that directional wire once until the electrons became confused and nearly ruined my stereo. Now I avoid it until I can find some smarter 'edumaketed' electrons.

The ones that riffster had pictured are an MDF sandwich with fiberglass bread.
This is how I had intended to build mine, regardless if there is pegboard on one side or not.

As a side note, I haven't been around the forum a lot lately. I recently started looking around again, and I have to say that I enjoy the new SAC quite a bit.
It's good to have you here.

Electrons are lemmings.

[Seamus TM]

Originally Posted by iriegeorge

Your images are very similiar to gobo's that I have, with the exception that on the absorbative side we left is thicker and split that side with a wood strip and gave it a convexed shape.

Cool.
I am having trouble visualizing it, though.
Got pics?