I feel that Bit's question is quite pertinent.

I've been reading that 8 lbs/cu foot works great in corners and that 4 lbs/cu foot is real good for placement along flat surfaces like walls.


best regards,
mike

bitflipper


If "denser is better", why not just stack up some concrete building blocks?

(Not arguing against the premise, just trying to provoke thought.)

The densest form of rockwool is called a window pane, but common sense would tell me that there's a happy medium nearer the denser end of not very dense at all.  IOW dense enough.

Get the slide rules and calculators out, fellas, here it comes, it's fart skinning hour again...

If "denser is better", why not just stack up some concrete building blocks?  

WITH ACOUSTICS..


and recording.

there are two parallel issues.

1. acoustic isolation (noise proofing)
2. acoustic treatment (preventing unwanted reflections, standing waves, etc)


for isolation, nothing is better than mass.

insulated wood stud is better than insulated metal stud wall.

concrete block (unfilled) is better than insulated wood stud wall.
filled concrete is better than unfilled.

solid concrete is better than block. 

add brick on the outside, with an air gap...

and then you've got your room in a room scenario......

etc, etc.



for treatment, it has to be looked at on a case-by-case basis.

maybe for one room, midrange treatment is in order..
in another room, it's the low end.

different treatments, for different problems.

there is no 'one-size-fits-all' for this issue.

Exactly.

Building materials are accredited also for acoustic isolation properties and acoustic treatment.

The fart skinning has doubtless been done to ISO standards already.

Just choose accordingly.   The ISO standard material will bring piece of mind at the extra cost incurred for the material to have gained the accredited standard in order that an architect can specify it by name and be sure it does what it is supposed to, isolate or treat reflections.

Or choose the nearest generic materials having the properties you want, then have doubts and wonder about it ad infinitum if you wish.  You may also choose breeze blocks even if you like but they likely wouldn't have the desired effect now would they?  Just guessing there tho.

The best way to keep a boring debate open is to recommend a generic material and then bring up the idea that variances to that may cause favourable differences or not.

It's enough to make me want to hire a specialist rather than get the best deal...

The 703 now sounds like for a few pennies more you'd at least get some peace of mind.

The best way to keep a boring debate open is to recommend a generic material and then bring up the idea that variances to that may cause favourable differences or not.

 
Or maybe something like this: Peter D'Antonio of RPG Diffusor Systems has said:

When attempting to control reflections with a single density material, it is fair to say that thin fiberglass panels should not be used, and in  my view lower density is preferred over higher density.
 

So 'denser the better' is not really a useful rule of thumb in the context of sound absorption. (not sound isolation)
 
And yet, my walls have many thin fiberglass panels on them. Go figure.

Perhaps what he was alluding to is that a "single-density material" is going to have optimal effectiveness for a specific range of frequencies, with its effectiveness dropping rapidly outside that range. 

You can actually hear the effect when you employ too much absorption. The room starts to sound muffled and unpleasant, while low-frequency issues remain mostly unaffected. That's how most people end up with too much absorption in the first place: they keep adding more in an attempt to trap low frequencies that are outside the absorber's range of effectiveness.

Ultimately where this takes you is a room response that's actually less flat than what you started with. It would make sense, then, to use different weights and thicknesses around the room to avoid that effect.

There is also a benefit to using multiple layers of lower-density material, so that you end up with the same mass but greater volume. The thicker the material, the more likely you are going to catch a given frequency at its maximum excursion, where the most energy is absorbed.

I built a bunch of traps about 3 years ago. I found another brand available locally at an insulation distributor with pretty much the same specs as 703. I can't remember the brand name for the life of me at the moment, so that's not much help other than the fact that there are other products out there that are equivalent.

probably roxul, we covered that one already

If you're looking specifically at bass traps, 705 density may be more appropriate. It's 100kg/m^3 vs 703 at 50 kg/m^3. I think. Does that sound right? Thus you can save space for the same level of trapping.

matt,

That does make sense.

Only problem I am having now is where to buy this stuff in the quantity I need. Seems like the places that can order it need to have a minimum that is way too much for my needs (as in 5 pallets worth).

Any suggestions on that?