John Sayers' Recording Studio Design Forum Archive

Hello there,
I have a small amount of acoustics knowledge but spent a long time reading various posts in this and 'Gearslutz' forum.
I am currently trying to make the best of a poorly designed small control room.
The dimensions are L-175", W-156", H-100"....

I am wanting to build corner bass traps on the rear wall and acquired some Rockwool RW5.
( http://www.building-supplies-online.co. ... 3754-p.asp )

I understand from reading forums that this stuff is very dense and hence not ideal for use in a superchunk design?
Would a corner panel membrane be a better use for it or should I put my hand in my pocket and buy a more appropriate insulation to superchunk?

I intend to build them in the rear 2 vertical corners and the rear horizontal. The front wall to the rear of the monitors has Auralex bass traps along the horizontal and it isn't possible to do the vertical corners due to a door and window.

If the RW5 isn't ideal, I was planning on using it for ceiling clouds in the live room and above the mixing desk would this be an appropriate use?

Any input would be greatly appreciated and I hope I have followed forum guidelines.

Hi Glover, and welcome!

I understand from reading forums that this stuff is very dense and hence not ideal for use in a superchunk design?

Yes, that is too dense. It is about twice as dense as what you should be using for bass traps. For mineral wool, it should be roughly 50 kg/m3. For fiberglass, about 30 kg/m3.

Would a corner panel membrane be a better use for it

Do you mean a membrane trap in the corner, or are you talking about just putting a "panel" of that stuff across the corner?

To be honest, that stuff is just too dense for effective bass trapping. Contrary to popular belief, higher density absorption is NOT better for low frequencies: it is WORSE for lows, and better for highs. For bass trapping, it is actually better to use less dense absorption.

I'm not saying that the stuff you have won't work: it will, but it just won't be very effective for lows. It would be fine if you needed something to absorb mostly mids and highs.

The issue is that it isn't really the density that matters. What REALLY matters is the "gas flow resistivity", which is how the insulation reacts to gasses moving through it. "Gasses" such as air... That's the factor that actually has the acoustic benefit. It turns out that mineral wool of 50 kg/m3 happens to have optimum gas flow resistivity, while for fiberglass the optimum number is around 30 kg/m3. If you go much higher or lower in density, then you start loosing effectiveness, because the gas flow resistivity is now too high or too low.

So the bottom line is that you COULD use what you have, and it WILL work as a bass trap, to a certain extent, but it will be more effective at taking mids and highs out of the room than it will be for lows.

- Stuart -

Thanks for your reply and incite Stuart! Really appreciated.

Soundman2020 wrote:Do you mean a membrane trap in the corner, or are you talking about just putting a "panel" of that stuff across the corner?

I was thinking of a membrane trap in the corner, I've read that for small rooms these aren't ideal either? I'd consider my room small. I think i'll dig in my pocket and buy the 50kg/m3 mineral wool and superchunk the corners.

Sounds like the stuff would be good for a ceiling cloud between the mix position and monitors and in the live room....1st things first though, time to get my saw, drill and stapler out and tame the bass.

Thanks again

G

I was thinking of a membrane trap in the corner, I've read that for small rooms these aren't ideal either?

You can use membrane traps in small rooms, if you need to. It's diffusers that have no place in small rooms (or rather, most types of diffuser).

A membrane trap (a.k.a. panel trap) is a tuned device: Usually a large piece of thin plywood mounted over a shallow sealed "box" with some insulation inside. It is tuned by selected the right thickness of wood and the right depth for the cavity. So it resonates at a specific frequency, which can be pretty low, if you want it to. Normally you would use one as a "last resource" to treat a stubborn room mode that refuses to submit to other treatment, and since a panel trap can be tuned quite specifically, it's easy to hit the exact frequency that is causing trouble, without affecting the rest of the low end.

Yes, you can also angle the front panel of a membrane trap, so that the cavity depth varies, and therefore broaden the range of affected frequencies, but I still wouldn't call it a true broadband device.

So you only really use it of you have a problematic frequency, or range of frequencies.

- Stuart -