Owen Corning 703 or subistitue in Canada?

[intellijel]

From what I have read there may be several suitable substitutes for Owen Conrning 703. However, I need to know what is good but available in Canada (I live in Vancouver).

Where can I buy here? What should I buy?


These are for building bass traps....


thanks!

[avare]

Roxul 4 lb/ft^3 mineral wool. Made in Grand Forks.

Best bang for the buck: Roxul Safe n Sound.

[danbronson]

I was really hoping that wasn't a typo and you actually thought it was spelled "subistitue". Say it out loud haha.

Okay...



+1 on Roxul. Safe & Sound is good bang for the buck and easy to find, according to specs, it seems Rockboard 60 might be the best for low end absorption however. You'll probably have to go through commercial or industrial suppliers to get it.

[avare]

Originally Posted by danbronson

it seems Rockboard 60 might be the best for low end absorption however.

We are writing about bass traps. Assuming that he will use at least 4" (100 m) thick material, 60 is actually slightly worse than 40, or going thicker 25 Rockboard. This is not an intuitive concept. The best I suggest to try and explain it is this thread.


All other things being equal, which they rarely are in prices of insulation, the price varies as a direct function of density. Bulk orders, overstocks, leftovers from orders make the price relationship a wild card. The good news is that the difference the 25, 40 and 60 acoustically is so small that the choice can be made on the basis of price and not have to worry about performance. Of course Safe n Sound is 1/8 to 1/12 the price of Rockboard. That has been the range here in Hamilton.

[danbronson]

Ack! Okay, I read through the thread. You weren't kidding, it's not intuitive. But I think I have a much better understanding now, especially thanks to the Porous Absorber Calculator (the excel spreadsheet).

So correct me if I'm wrong, but the thicker the absorber and air gap, the lower the frequencies you can absorb BUT as those factors change, the ideal absorber changes as well. Looks like for 6" thick with a 6" air gap behind, something with a gas flow resistivity of 6,000 rayls/m is ideal. That's not much at all! In fact, it seems to me that fluffy fiberglass might be pretty close to that.

Any idea how I can calculate the gas flow resistivity of different Roxul products to determine the ideal one?

[avare]

Originally Posted by danbronson

Ack! Okay, I read through the thread. You weren't kidding, it's not intuitive.

So correct me if I'm wrong, but the thicker the absorber and air gap, the lower the frequencies you can absorb BUT as those factors change, the ideal absorber changes as well. Looks like for 6" thick with a 6" air gap behind, something with a gas flow resistivity of 6,000 rayls/m is ideal. That's not much at all! In fact, it seems to me that fluffy fiberglass might be pretty close to that.

Any idea how I can calculate the gas flow resistivity of different Roxul products to determine the ideal one?

My bolding of the correct answer. Having to get into the technical stuff, the theoretical goal is for the impedance at the surface of the absorber to match the acoustic impedance of air (412 Rayls). Fortunately the effect of surface impedance is relatively minor with the resistivities of the materials we use for absorption. This ignoring that the material has to be where the kinetic energy (velocity) is high.

As you have already figured out, getting data on the resistivity of various materials is very difficult. We use material density as an indicator of resistivity. Looking at OC data on absorption of various densities of materials, the trends that might be overlooked by someone not familiar with the physics involved would overlook. As an example how at 125 Hz 4" 703 is more efficient than 705. The trend between density and resistivity also varies between fiberglass and mineral wool, just to make things even more counter intuitive.

Coming back to what you asked about 6/6 absorbers, yes fluffy fiberglass is close to optimum theoretically. The reason I say theoretically, is that when working professionally in acoustics, I never want to recommend anything without test data to confirm what I recommend unless it can be interpolated from current test data or knowledgeably extrapolated.

I hope many people read this thread and get an idea why a question that seems simple to answer is not.

Andre

[danbronson]

Thanks very much Andre. Very informative! I PM'd you another question (that I have a feeling won't be clearly answerable) because I didn't want to hijack this thread any further.

One more question though (I can't stop! haha), is it safe to say that as density decreases for a given brand's product (I know that's kind of vague, but in the case of Roxul for example, all their products are somewhat similar, right?), the air flow resistivity also decreases? This ties in with the question I PM'd you actually. Essentially, can one assume that Roxul Safe & Sound has a lower resistivity than Rockboard 35, because it's density is lower?

Okay, after this I'm done hijacking the thread!

[avare]

Originally Posted by danbronson

Okay, after this I'm done hijacking the thread!

you haven't hijacked it, just brought to a different level. If you want a direct on topic reference here it is.

Intellijel;

as you have read in last couple of posts, if you want best possible in terms money or acoustic performance or both, give more information.

On topic.

Andre

[avare]

Originally Posted by danbronson

is it safe to say that as density decreases for a given brand's product (I know that's kind of vague, but in the case of Roxul for example, all their products are somewhat similar, right?), the air flow resistivity also decreases?

Generally yes within the range of materials we use. The relationship is NOT linear though.

Andre

[intellijel]

Hi Avare,

Sorry for the late reply on this thread!

My priority is definitely acoustic performance over price but obviously price is always a factor.

My room is fairly small: 8.5' x 11' with 8' ceilings. There are obviously some serious room mode issues when it is this small.

So with those dimensions I need to be taming the (approx.) 100Hz, 135Hz and 140Hz room modes (never mind the diagonals etc.)

So I would hope that 4" thick 2x4 panel bass traps placed on each corner and broadband panels placed at the first reflection points should all help deal with the situation.

cheers,
intellijel

[avare]

Yes the treatment you described will help with the lowest modes. BTW the lowest modes are one octave lower. That is 50, 67.5 and 70 Hz.

Enjoy!

Andre

[Swansonic]

seach for "steels" there is a outlet in Surrey and Burnaby.
they have 703.