Broadband Absorber Question

[DanDan]

If you can find the Gas Flow Resistivity of the product you could predict the absorption spectrum using this calculator.
Porous Absorber Calculator

I haven't seen great performance from the 24 inch SSC's, while the 34 inch ones rock.

You will almost certainly be sitting the Height and Width nulls, so it would be well worth trying for some LF absorption at your Cloud and Sides.
6" plus an airgap would be good.

DD

[bfrance]

Originally Posted by DanDan

If you can find the Gas Flow Resistivity of the product you could predict the absorption spectrum using this calculator.
Porous Absorber Calculator

I haven't seen great performance from the 24 inch SSC's, while the 34 inch ones rock.

You will almost certainly be sitting the Height and Width nulls, so it would be well worth trying for some LF absorption at your Cloud and Sides.
6" plus an airgap would be good.

DD

Thanks for the input. I have a message into Thermafiber's tech support to try to find the GFR numbers for the material.

-Ben

[bfrance]

And so much for that....

The only GFR numbers that they could provide was for 4.0 pcf density Safing Insulation (totally different product.)

Any other ideas on how to calculate this, or do you think that I'd be safe to go with 2 3" pieces deep, for 6" total in material, plus some airspace behind it (thinking of usuing 5/4x8" boards for the absorbers, so that would allow 2" of airspace behind if I didn't space them from the walls at all.)

Thanks again,

-Ben

[DanDan]

Without GFR figures we can only guess. But you could base your guesses on materials of similar density. Common Gas Flow Resistivity numbers.

2.5 pcf is approx 40KG/M^3

I think the stuff you have will be just fine at those thicknesses.

DD

[bfrance]

Originally Posted by DanDan

Without GFR figures we can only guess. But you could base your guesses on materials of similar density. Common Gas Flow Resistivity numbers.

2.5 pcf is approx 40KG/M^3

I think the stuff you have will be just fine at those thicknesses.

DD

Okay,

Another quick question for you. On my superchunk corner traps, the rockwool wants to lean over and fall once I get above about 8 triangles or so. Would there be any downside to covering the front face of the traps (behind the finish panel,) with 6mil plastic (I have a huge roll of this left over from our gardening)? If not, I think this is going to be the easiest way to keep the traps vertical.

-Ben

[DanDan]

Make open shelves, like in this design. Corner Traps finally finished! - Home Theater Forum and Systems - HomeTheaterShack.com
These triangular wooden frames also provide a place to screw on the front facing.
DD

[bfrance]

Originally Posted by DanDan

Make open shelves, like in this design. Corner Traps finally finished! - Home Theater Forum and Systems - HomeTheaterShack.com
These triangular wooden frames also provide a place to screw on the front facing.
DD

That's pretty much exactly what I'm doing. I got my inspiration (okay, my copied design,) from this thread: My DIY SuperChunks Plus & Soffit Corner Traps (Pics)

The problem that I"m having is that the Thermafiber RW that I bought is 2.5 pcf, so it's kind of floppy and when I get more than about 5-6 pieces stacked they started to lean/topple out of the corner. I'm thinking of temporarily putting a piece of masking tape in the center of them from the floor "shelf" to the mid "shelf" and from the mid "shelf" to the top "shelf", then stapling 6-mil plastic to the front of the shelves to permanently hold the RW in behind the grills. My only concern is whether the plastic would affect the bass-traping. I'm assuming not....

-Ben

[kasmira]

People recommend plastic a lot here, particularly to not deaden the high end too much. 6mil is right at the suggested cutoff of where it will/won't absorb most mid/high freqs. If you're looking for a truly broadband approach, you may want to use thinner plastic (or none at all) - but if you want them to be mostly bass traps, and not suck up as much treble (which is generally a good thing if you have other absorbers in your room) it will be perfect.

[DanDan]

Ben, shelves are the answer. Normally three are enough, but if your stuff is particularly floppy four should do it. Slightly squeeze the fibre in there and it show stay. Otherwise you will have to do some light cross framing. People use plastic, particularly in overhead Clouds. I prefer to use commercial traps for overhead, which contain the fibre without blocking any sound.
DD

[bfrance]

Originally Posted by DanDan

Ben, shelves are the answer. Normally three are enough, but if your stuff is particularly floppy four should do it. Slightly squeeze the fibre in there and it show stay. Otherwise you will have to do some light cross framing. People use plastic, particularly in overhead Clouds. I prefer to use commercial traps for overhead, which contain the fibre without blocking any sound.
DD

Well, squeezing the rock wool in worked, along with putting 2 sides "frames" of 1x2 boards on them. I still covered them in plastic just to help prevent the possibility of fibers from becoming airborne. Amazingly, just having the two superchunks in the room has made a noticable difference in the overall acoustics.

I'll be making my mirror-point absorbers tomorrow and hopefully getting the "grills" done for all 4 panels. Once that is done and I get a nice rug in the room I'll take measurements and decide if I need more bass trappings.

-Ben

[DanDan]

Nice one. These days I would always included light laths across the front.
About 50% of the area, using Newell's 345 pattern.
IMO looks better than fabric, stops people poking, and has a small HF bounce, with no downsides.
DD