Bonded Acoustical Cotton . Is it good?

bpape · « **Reply #20 on:** 16 Jun 2005, 08:59 pm »

703 is tough to beat. It's very a very flexible product. Like I said, for the corners and where you need that little bit extra at 250-500, the BAC is great.

I rarely use anything but 703 from a fiberglass standpoint. However, for reflection points on the side and the broadband bass absorbtion, I almost always use BAC if the budget will allow. The other areas can save some money and use 703 just fine.

klh · « **Reply #21 on:** 16 Jun 2005, 11:56 pm »

Thanks for the spirited discussion! You make good points.

Ethan Winer · « **Reply #22 on:** 17 Jun 2005, 04:48 pm »

bpape,

> For reference though, look at the numbers for OC 701, 703 and 705. The 701 is the best performer down low - not the higher density board. <

I'm surprised to see you say that because I'm sure you've seen my Density Report, no?

The problem with most published absorption data is they show A mounting (flat on a surface) only, and ignore what happens below 125 Hz.

--Ethan

ctviggen · « **Reply #23 on:** 17 Jun 2005, 05:01 pm »

Ethan, those are cool graphs! It's amazing what those treatments do.

klh · « **Reply #24 on:** 17 Jun 2005, 09:01 pm »

Ethan... thanks for the link! Those waterfall plots sure are cool

bpape · « **Reply #25 on:** 18 Jun 2005, 12:59 pm »

Actually, they also show what happens with a 16" airspace and the 701 is still doing a better job at 125 and 250 - not by much but for the price difference for a specific application, why not.

I saw your density reports. I've read and looked at them several times. I'm still digesting and thinking about the results as some are counter-intuitive to my experiences. I'm just still getting my arms around the WHY of the results so it makes sense to me.

ctviggen · « **Reply #26 on:** 18 Jun 2005, 05:28 pm »

The FRK version does a slightly better job at the lowest room mode in the 12 piece version. I would expect that, as the FRK probably vibrates and absorbs at lower frequencies because of that. Also, higher density is better for low frequency absoption, which also makes sense. What about high frequency absorption? Did you analyze that? (I would think higher density would be better for that, too.)

Ethan Winer · « **Reply #27 on:** 19 Jun 2005, 02:20 pm »

Bob,

> What about high frequency absorption? <

At higher frequencies the less dense types are better for two reasons. First, the denser boards have a "harder" surface and so reflect more at higher frequencies. Also, with higher density fiberglass, sound that strikes at an angle tends more to "ricochet" off the surface.

--Ethan

bpape · « **Reply #28 on:** 20 Jun 2005, 02:42 pm »

Exactly Ethan. So if I use something less dense, I get less 'bounce' and potentially better bass absorbtion.

I've been looking more at your findings. I'd agree that once you get beyond 4" (for rigid glass) it's diminishing returns. For bass absorbtion, more surface area will beat more thickness and same surface area.

Ethan Winer · « **Reply #29 on:** 20 Jun 2005, 06:24 pm »

bpape,

> So if I use something less dense, I get less 'bounce' and potentially better bass absorbtion. <

I don't think that applies so much at bass frequencies. Forget FRK and just look at the data for plain 3-inch 701 versus 705. The upper graph shows 701 and the lower shows 705:

At the lowest two modes the difference is slight - that's where FRK makes a bigger improvement - but look at how much better the response and ringing are with 705 above 80 Hz.

--Ethan

brj · « **Reply #30 on:** 20 Jun 2005, 06:42 pm »

Ethan, have you done any similar tests with 701/703/705 +- FRK & thickness on just the first reflection points? Since you were treating the entire room for the plots you showed, I'm having a hard time drawing conculsions specific to the reflection points alone...

Thanks!

bpape · « **Reply #31 on:** 20 Jun 2005, 07:33 pm »

Understood Ethan. The response is a little better with 705. The bounce I was talking about was at higher frequencies. When I use unfaced, I count on that too and certainly don't want highs skipping off the face creating another reflection point to deal with on the side walls.

I'm curious though why you used 3" instead of 4" for the tests? Just what was on hand? If we're really talking about sheer bass absorbtion, wouldn't you agree that 4" of 703 would be better than 3" of 705?

Ethan Winer · « **Reply #32 on:** 21 Jun 2005, 03:37 pm »

brj,

> have you done any similar tests with 701/703/705 +- FRK & thickness on just the first reflection points? <

No, because first reflections are mainly a mid and high frequency issue, and getting high absorption there is easy. Two inches of 701 or 703 are known to do a fine job for that.

--Ethan

Ethan Winer · « **Reply #33 on:** 21 Jun 2005, 03:40 pm »

bpape,

> The bounce I was talking about was at higher frequencies. <

Agreed. I was talking about bass trapping only.

> I'm curious though why you used 3" instead of 4" for the tests? Just what was on hand? <

Yes, that's what we had.

> If we're really talking about sheer bass absorbtion, wouldn't you agree that 4" of 703 would be better than 3" of 705? <

I never tested that specific combination so I honestly don't know. And for "sheer bass absorption" you'd want to compare the FRK types anyway.

--Ethan