About the traps and absorbers...Ethan & Co.

[11miles]

Hey guys.

I've found a way to get a hold of some material.

What i was wondering, how much would you say is enough to treat a room, size, 4.6*2.6m
And where to put the absorbers.
I saw some pics on the Ethans page, that are on the ceiling, some on the corner and some on the walls.

Any suggestions.

I am going to buy them tommorow and i would like to get a holdof some and then calculate the positioning.
So any info on that would be great.

Thanks

[KevinDrummer]

The RealTraps website says you can put them about anywhere and the more the better. Corners are preferred.

I just came here to post a related thread when I saw this, so I'll post it here.

I can't afford the RealTraps. Anyone know how they are constructed so I can do them myself (or get close, anyway)? I would probably want to do a combination of Mondo traps, mini traps, and micro traps, with most of them also including the HF absorbing front panel.

Thanks in advance.

[Innovations]

For DIY almost-as-good-as-realtraps seek out a source of Owens-Corning 703 fiberglass. Wrap four inch thick (for full spectrum traps) or thinner (for progressively less low frequency absorbtion) stacks in accoustically open fabric (burlap, felt, etc) and hang with an airspace behind.

[KevinDrummer]

Originally Posted by Innovations

For DIY almost-as-good-as-realtraps seek out a source of Owens-Corning 703 fiberglass. Wrap four inch thick (for full spectrum traps) or thinner (for progressively less low frequency absorbtion) stacks in accoustically open fabric (burlap, felt, etc) and hang with an airspace behind.

Thanks. Isn't a membrane or panel with some mass attached to the insulation part of the system. Something thin like 1/4" ply? After a little research, it seem that they do. Would this kind of be a hybrid between a broadband absorber and a panel absorber?

[Innovations]

Originally Posted by KevinDrummer

Thanks. Isn't a membrane or panel with some mass attached to the insulation part of the system. Something thin like 1/4" ply? After a little research, it seem that they do. Would this kind of be a hybrid between a broadband absorber and a panel absorber?

Well, I did describe them as almost-as-good-as. I don't know the details of the internals of realtraps. If you look at just the absorbtion specs of the 703 though you realize that there really isn't anything 'missing' from just using the fiberglass itself. Given enough thickness 703 alone provides excellent bass absorbtion. So in the spirit of 'keep it simple' for a DIY project I recommended just using the 703.

[fitZ2]

Thanks. Isn't a membrane or panel with some mass attached to the insulation part of the system. Something thin like 1/4" ply? After a little research, it seem that they do. Would this kind of be a hybrid between a broadband absorber and a panel absorber?

I thought you had a physics background? A membrane or panel with some mass attatched to the insulation? For what? Maybe I don't understand the question. Absorbers such as rigid fiberglass need nothing. You could simply stand them on the floor up against the wall and they perform their function. The reason for the airgap between them and the wall, is because the velocity of air particles at a boundary is ZERO, but pressure maximum. At 1/4 wavelength, their velocity is greatest. Hence, thicker panels absorb a longer 1/4 wavelength which translates into a lower frequency. If you place the fiberglass against the wall, you are actually wasting a portion of the thickness for nothing. If you use something to stand it away from the wall 1/2" to 1", you increase the working thickness, which in effect, lowers the bandwidth. Spacing 1" thick material out 3" will increase its absorption to about what 2" material will do mounted directly to the wall.
To answer the other part of your question, no, it does NOT create a hybrid. Either it is a membrane absorber, or a resistance absorber. However, membrane absorber absorbs by resonance, and as such, REQUIRES a sealed air cavity between two membranes, such as the air cavity in a WALL. Although it is a narrow bandwidth. The sheetrock becomes the membranes, with a resonant frequency determined by the density of the membrane, and the depth of the cavity. I have read that the absorption coefficient of 1/2" drywall on studs 16" oc at 125hz is .29. That is almost a 1/3 of a sabine for every square ft of drywall. It even has a higher coefficient at 63hz, which is even lower frequency. Many newcomers to studio building do not realize that they have an abundance of FREE BASS TRAPS built-in to their rooms already. However, the more layers of drywall, the stiffer the membrane, the higher the frequency of absorption. Increase stud spacing to 24", and it lowers the frequency. This is why studio designers must include drywall absorption calculations for the entire room to predict RT-60 values.

here is the formula. but its hard to write formulas this way
f(freq in hz)=170/square root of (m) (d)
m=surface density of membrane(lbs/sq' of panel surface
d=depth of airspace(inchs)

The use of fiberglass insulation within the cavity, is for dampening the membrane, which lowers the Q( I believe). Also, you can place a resistance absorber on the face of a membrane absorber with a small airgap for High Frequency absorption in the same space. I guess you could call this broadband or a "hybrid" when used together.
A better type of low frequency absorber for homestudio users is Slat absorbers with varied slot and slat widths. These can be built into INSIDE-OUT wall assemblies, or simply as gobos. They are in essence, a Hemholtz Resonator.

fitZ

[11miles]

So the more the better you say?

But wont that get the room sounding to dead?

I mean that is the problem with wrapping the room in acoustic foam, right?

[KevinDrummer]

Originally Posted by 11miles

So the more the better you say?

But wont that get the room sounding to dead?

I mean that is the problem with wrapping the room in acoustic foam, right?

Well, I don't say - but the RealTrap website does. It's hard to get it "too dead" in the low freqquencies, but of course you need to watch out for the higher freqs. That's why you can get them with the option of their "face" being reflective or absortive.

I did find a review of these panels that decribed a little of their construction, and it does include a membrane (of unkown thickness/material)

http://www.recording.org/e-mag/article_109.shtml



Oh, and FitZ:

I never said I had a "physics background". In another thread I said I "understood the physics" of what was being explained. I have a better than average grasp of the subject, but I'm sure no expert in all the nuances of accoustical physics/engineering.