Bass trap technical questions

[Yetti]

Hi Technical acoustics Guys,
I was given a free box of six 2' x 4' x 2" 703, and a roll of prelude fabric.
My acoustics are pretty good in my live room and control room (pics attached), but I figure what the hell...I will build a bass trap or 2 out of these free materials.
My intention is to build wood frames on stands so they can be portable and not mounted..I would probably place bass trap or traps in the live room when tracking, and then move into the control room for mixdown...wonderful.

Now the technical questions;
1) Is it better bass absorbsion to build one 12" thick 2' x 4' panel, or build two 6" thick panels?
2) Is the Prelude fabric a good choice, or would I actually get more bass absorbtion using a lighter sheer type fabric?

I'm sure these question have been asked before, but I decided to forget the search function and have some conversation with my GS Brothas.

Thanks in advance!!

[tINY]

If you are going to make it portable, I'd put a sheet of 5/8" plywood in the middle of two panels and call it a gobo....



-tINY

[Weasel9992]

I guess I agree with tINY on this one, but if you're going to make panels instead, I'd do two 6" panels rather than a single 12" panel.

Frank

[Yetti]

I thought it would absorb bass better if it there wasn't a plywood panel in the middle... Am I wrong?

I already have a couple gobo panels, but normally I place amps in another room, and vocalist can be on the other side of the control room glass...

So my first 2 post questions are still waiting for a techy answer.....

[Ethan Winer]

You are correct, a barrier in the middle will worsen bass absorption, but make the panel better as a gobo if you can benefit from that double-duty. If you don't them as gobo too, leave out the barrier.

--Ethan

[Yetti]

Originally Posted by Ethan Winer

You are correct, a barrier in the middle will worsen bass absorption, but make the panel better as a gobo if you can benefit from that double-duty. If you don't them as gobo too, leave out the barrier.

--Ethan

Alrighty, so I again refer to my reason for posting in regards to Bass traps
2 technical questions;

1) Is it better bass absorbsion to build one 12" thick 2' x 4' panel, or build two 6" thick panels?
2) Is the Prelude fabric a good choice, or would I actually get more bass absorbtion using a lighter sheer type fabric? (PDF Specs attached in first post)

[R_O]

Understand this; wool will absorb any frequency. The thicker the wool (depth), the lower it'll absorb. But it'll still, also, absorb all the higher frequencies.

In order to have it absorbing low-end exclusively, you need to put "filter" in front. That'll reflect higher frq but still absorb lower frq. A lowpass filter so to speak

A filter can be anything from a sheet of plastic to heavy cloth to a wood panel. The denser the filter the more it'll reflect high frq resulting in a more exclusive bass absorbing device.

So, the stuff you got could work if it has some descent mass (didn't read the specs)

[Weasel9992]

Originally Posted by Yetti

1) Is it better bass absorbsion to build one 12" thick 2' x 4' panel, or build two 6" thick panels?

I answered this in my post above:

"...but if you're going to make panels instead, I'd do two 6" panels rather than a single 12" panel."

Originally Posted by Yetti

2) Is the Prelude fabric a good choice, or would I actually get more bass absorbtion using a lighter sheer type fabric? (PDF Specs attached in first post)

The specification doesn't really say much that's valuable, but I'll say this: 9oz. fabric is pretty heavy. You're getting in the ballpark of theater-weight stuff once you get to 11oz. I can't say for sure without holding it in my hand, but just see if you can blow through it. If you can, it's fine.

Frank

[Yetti]

Originally Posted by R_O

Understand this; wool will absorb any frequency. The thicker the wool (depth), the lower it'll absorb. But it'll still, also, absorb all the higher frequencies.

In order to have it absorbing low-end exclusively, you need to put "filter" in front. That'll reflect higher frq but still absorb lower frq. A lowpass filter so to speak

A filter can be anything from a sheet of plastic to heavy cloth to a wood panel. The denser the filter the more it'll reflect high frq resulting in a more exclusive bass absorbing device.

So, the stuff you got could work if it has some descent mass (didn't read the specs)

That makes sense, and yes I am most interested in bass trapping.
If I approach this from my own non technical guess, I would think using this Prelude 1/8" thick fabric is dense, and therefore would be better at "filtering" the highs.
But again, I have attached the PDF specs and pictures, looking for a tech answer
Now the technical questions;
1) Is it better bass absorbsion to build one 12" thick 2' x 4' panel, or build two 6" thick panels?
2) Is the Prelude fabric a good choice? (PDF Specs in original post),

[Yetti]

Originally Posted by Weasel9992

I answered this in my post above:

"...but if you're going to make panels instead, I'd do two 6" panels rather than a single 12" panel."



The specification doesn't really say much that's valuable, but I'll say this: 9oz. fabric is pretty heavy. You're getting in the ballpark of theater-weight stuff once you get to 11oz. I can't say for sure without holding it in my hand, but just see if you can blow through it. If you can, it's fine.

Frank

The prelude fabric is pourous enough to blow through, but yeah it is about 1/8" thick and pretty dense...like thick felt.
If I can catch more bass in a room building 1 12" thick trap rather than 2 6" thick traps, yeah...it would be less work to build only 1 portable frame.
If that is the fact, that is what I will do...but if it is speculation, or if factors such as room size and placment are a considerable part of the decision, those are the really the type of technical answers I am looking for.

Thanks for you input!

[Weasel9992]

Originally Posted by Yetti

If I can catch more bass in a room building 1 12" thick trap rather than 2 6" thick traps, yeah...it would be less work to build only 1 portable frame.
If that is the fact, that is what I will do...but if it is speculation, or if factors such as room size and placment are a considerable part of the decision, those are the really the type of technical answers I am looking for.

Let me explain it more fully. The rule of thumb is that coverage *always* trumps thickness. In other words, if you have enough material to build four 8" traps or eight 4" panels, *always* go with the higher number of thinner panels unless there's a specific reason not to. The reason is that you're going to do have much more impact in that critical 70Hz-350Hz range by using more panels deployed appropriately than with fewer but thicker panels. Remember it's not just the room response we're trying to impact; it's also the decay time. Make sense?

Of course room size and panel placement figure into the equation, but those are different questions than the one you're asking with respect to panel thickness vs. coverage.


Frank