Using 703 FSK For Clouds..?

[DanDan]

Foil facing airgap/ceiling. Very similar to RT MicroTraps.
Doubled up foil removed in side the sandwich, i.e. 4 inch, with a 4 inch gap would be better IMO.
DD

[jim1961]

In my case, I used unfaced 2" 703 with 6" of R19 behind it for my ceiling cloud. Seemed to work better than 4" 703 with a 4" airgap.

[DanDan]

And cheaper I expect.
DD

[Snatchman]

Thanks for the reply guys..So, the 703 FSK with the foil facing the ceiling is ok..? ( even better if I double it up and remove the foil off one piece). With the foil facing the ceiling, is the foil even in existance in this configuration?. I know with the foil facing towards the room, it send mid/hi's back into the room..If using this in several clouds, would it be of any advantage to use some in both directions to sorta balance out bass and mid/hi absorption..?( keep some "air" in the room)..Thanks..!

[jim1961]

Originally Posted by Snatchman

Thanks for the reply guys..So, the 703 FSK with the foil facing the ceiling is ok..? ( even better if I double it up and remove the foil off one piece). With the foil facing the ceiling, is the foil even in existance in this configuration?. I know with the foil facing towards the room, it send mid/hi's back into the room..If using this in several clouds, would it be of any advantage to use some in both directions to sorta balance out bass and mid/hi absorption..?( keep some "air" in the room)..Thanks..!

The foil will keep sound from traveling beyond it. If you have a air gap beyond the 703, the sound wont see it cause of the foil. If you want the deepest bass absorption, take the foil off completely, both layers.

[kasmira]

Originally Posted by jim1961

The foil will keep sound from traveling beyond it. If you have a air gap beyond the 703, the sound wont see it cause of the foil. If you want the deepest bass absorption, take the foil off completely, both layers.

That's not really true. Foil will reflect treble, but treble will already be absorbed by the 703 by the time it hits the foil. Any frequencies under 1k or so will pass through the foil and it will be more like the foil isn't there. The foil acts as a membrane which can actually improve bass absorption by a bit.

Originally Posted by Snatchman

Thanks for the reply guys..So, the 703 FSK with the foil facing the ceiling is ok..? ( even better if I double it up and remove the foil off one piece)

Yep!

Originally Posted by Snatchman

With the foil facing the ceiling, is the foil even in existance in this configuration?

Depending on the frequency of interest, of course. The problem with introducing ANY new material in a trap is that each time a sound wave hits a material with a higher gas flow resistance there will be reflection. So, it will go through the 703 and some material will reflect off the foil. However, foil is so thin that only very high frequencies will be reflected, it will be invisible to any longer wavelengths. By the time sound has already passed through the 2" of 703, the left over frequencies would hardly be reflected (as they're all so large in wavelength in comparison to the foil's thickness).

Originally Posted by Snatchman

If using this in several clouds, would it be of any advantage to use some in both directions to sorta balance out bass and mid/hi absorption..?( keep some "air" in the room)..Thanks..!

Yes, absolutely. But it definitely depends per room. If you have a lot of absorption on the walls already, you may want more reflection. If you already have carpet, you don't have any flutter echo between the floor and the ceiling so there's no added benefit to absorbing more highs. In a room with hard flooring though, you may want more absorption on the high end and have less or no reflecting panels to combat flutter echo. If you did use some with foil on the front, and some without, make sure at least the panels in the first reflection paths do not have foil on the front. The ones that do reflect should be where indirect reflections are, not ones that come straight back at you (this goes the same for wall panels as well).

Good luck! How many were you thinking of building? If you can sacrifice the space, as noted above in Jim's first post, adding fluffy insulation above can really help introduce some very welcomed extra bass absorption. So, perhaps instead of four 4x2 clouds, you could have just one larger 32sq feet cloud with R19/R30 on top, hidden by the frame.

[jim1961]

Originally Posted by kasmira

That's not really true. Foil will reflect treble, but treble will already be absorbed by the 703 by the time it hits the foil. Any frequencies under 1k or so will pass through the foil and it will be more like the foil isn't there. The foil acts as a membrane which can actually improve bass absorption by a bit.

I am pretty sure that foil will stop frequencies lower than 1K.

If the foil has slits or holes in it, then thats a different story.

[kasmira]

Originally Posted by jim1961

I am pretty sure that foil will stop frequencies lower than 1K.

If the foil has slits or holes in it, then thats a different story.

You are correct, I think, but not sure as to how correct either of us are..

Originally Posted by F. Alton Everest, Master Handbooks of Acoustcs Fifth Edition, Pg. 188

When the [kraft] paper is exposed, it shields the glass fiber from sound above 500 Hz, but has little effect under 500 Hz.

You can also see in the graphs on Pg. 189 that a membrane such as FRK actually produces a peak of absorption (which the frequency looks to be almost completely related to depth behind the paper, of course). Also, this is remarks on tests of R11 and R19 (3.5" and 6" respectively) of pink fluffy, and not OC703.

With the R19 + Kraft facing the room, we see a peak at 250 Hz and it starts to drop above that. With the kraft against the wall, we see pretty even absorption above 250 Hz.

With the R11 + Kraft facing the room, we see a peak at 500 Hz and it starts to drop above that. Again, with the kraft against the wall we see even absorption at 500 Hz and above.

So, in short, you are correct, it may very well reflect frequencies 250 Hz or even small amounts below that depending on the depth of absorber. However, a less than 1mm thick layer of foil will not do anything near 'stopping' sound - if it did, it would be the holy grail of the isolation industry. And even though it may very well reflect some sound, we can usually get a diaphragmatic absorber with facing, which will give us a boost of absorption at certain frequencies that we could use to our advantage.

Edit: Moreover, those tests only show the reflection caused by FRK when facing the room and FRK facing the wall with no air gap. When materials are tested in type A mounting, they are against a hard backing. So the absorption coefficients show when sound goes through the panel twice. Once on the way through, and once again after it bounces off the wall and goes back through the absorber. If the FRK were to reflect, the sound still travels through a second time.

But...the absorption coefficients do show that the FRK do absorb less, but considering its use in commercial products, I assume it to be better than coefficients show

[Snatchman]

Hey guys..Thanks again for the informative replies..!..I'm probably gonna build 'bout 6 2' x 4' clouds.. As advised, I'll keep the clouds with the foil facing back into room out of the direct signal path..Thanks again..

[PaulRain]

I agree with Jim, use the 703 for the first layer, it's rigid enough to prevent the cloud to collapse (you'll need few wooden slats if it's big though) face the FSK towards the ceiling, then, over it, put some R19 (or anything similar)
go deep (6"-8") leave air behind, as much as your room height permit.

[kasmira]

Originally Posted by PaulRain

I agree with Jim, use the 703 for the first layer, it's rigid enough to prevent the cloud to collapse (you'll need few wooden slats if it's big though) face the FSK towards the ceiling, then, over it, put some R19 (or anything similar)
go deep (6"-8") leave air behind, as much as your room height permit.

+1

[DanDan]

If there is no airgap the foil has no function. I tested this foil thing some time ago. I reckoned the foil was causing a panel resonance which was sucking warmth in the 200-250 region. I stripped foil off 8 Minitraps in my cloud and sides. LF got sligthly worse so I reapplied the foil. A lot of work for nothing. HF MiniTraps have foil on the back, it's not an accident.....
DD

[PaulRain]

the thing is he already have the panels with the foil, I suggest to face it towards the ceiling to not have it facing the room....
can still have an extra 703 panel on top af all the fluffy still with the foil towards the ceiling

[DanDan]

As advised, I'll keep the clouds with the foil facing back into room out of the direct signal path..

Wha....? The purpose of the cloud is to eliminate HF reflections from overhead. Foil facing down into the room will generate reflections. You would have a sore foot from shooting it.

Cloud, Foil UP, no matter what. If there's a gap you will get a tiny LF absorption boost from the foil. If no gap, the foil is effectively not there.

DD

[Snatchman]

Originally Posted by DanDan

Wha....? The purpose of the cloud is to eliminate HF reflections from overhead. Foil facing down into the room will generate reflections. You would have a sore foot from shooting it.

Cloud, Foil UP, no matter what. If there's a gap you will get a tiny LF absorption boost from the foil. If no gap, the foil is effectively not there.

DD

"You would have a sore foot from shooting it."

Ha ha...Story of my life....Ok then, foil facing ceiling..Thanks..!