Facing on rigid fiberglass?

[bluespkr75]

Hello, I'm in the process of building some bass traps using 1 x 4 frames loaded with two sheets of 703 two inches thick per sheet. I wanted some hi/mid absorption so I peeled the paper off of the sheet facing into the room. So, my question is: Does it make sense to leave the paper on the 703 that is on the back side of the trap? The paper would be facing into the corner on the back. Has my thinking been correct here on how I built these?

[Eric_Desart]

Hello, I'm in the process of building some bass traps using 1 x 4 frames loaded with two sheets of 703 two inches thick per sheet. I wanted some hi/mid absorption so I peeled the paper off of the sheet facing into the room. So, my question is: Does it make sense to leave the paper on the 703 that is on the back side of the trap? The paper would be facing into the corner on the back. Has my thinking been correct here on how I built these?

75,

I don't think this combination is tested already.
I assume you use 703 FRK or something (the standard 703 has no paper).

Some thoughts.
50 mm for a corner basstrap is rather thin. Mostly people go for 100 mm or more.
Your reasoning of the absorbing surface is correct caused by the removed paper on the room side.

The paper on the backside will enhance the membrane behavior of your trap causing a peak (or more?) in the absorption spectrum.

There are different visions about this.
Whether this is good or not in your case you could try.

I prefer naked thick wool (or chuncks but that's more expensive per absorbed unit, but shows a better curve).

It's already difficult to exactly explain/understand the behavior of measured corner absorbers, hence it's certainly difficult to exactly predict deviating special designs.

Any corner absorbtion measurement I saw until now (and that's more than what you find on the net) shows a resonant peak behavior. (with 1 single exeption: the extreme bad FBM corner absorber measurements)
In fact it is a combination of 2 overlapping curves
1) Some kind of resonance absorption peak.
2) A dip (depth depending of type) separating this resonance and subsequent absorption noted in 3)
3) A subsequent curve more logical related with wavelength and edge effect.

A membrane on top not only diminishes mid and high absorption but also enhances this narrow resonant peak.
3 known measurements confirm this behavior.
Whether this is good or not are different visions about it.

The chunks fill in this dip making a smoother absorption curve.

[bluespkr75]

Yeah, I used 703 FRK. I was unsure what to do about the facing after reading about test results that Ethan Winer posted a link to.

I'm very new to this whole acoustics thing so I'm a little unsure about some things. Most of my problems in my room result in unclear lows in my mix position (or atleast that's my biggest concern right now). My room is 10x18x9 and I'm set up on one end of the room.

So, what kind of frequencies can I expect to be targeting with the absorbers that I have built? I did do an analysis before I started this whole project and noticed a major peak at 129 Hz and a huge dip at 75 Hz.

I do have to say though, after installing three of the absorbers that I made, I noticed an improvement just in casual listening.

[Eric_Desart]

I'm very new to this whole acoustics thing so I'm a little unsure about some things.

Don't worry .... after close to 30 years busy with this stuff I still have the same problem as you here.
The more one learns the more additional question marks one has.

So, what kind of frequencies can I expect to be targeting with the absorbers that I have built? I did do an analysis before I started this whole project and noticed a major peak at 129 Hz and a huge dip at 75 Hz.

If you read my post you can see I can't answer this.
The best way is trying and testing and listening.
But I think it's an unjust saving trying to safe a little bit of fiberglass thickness here.