Hi fellas,

Hard facts about DIY acoustic panels:

1. Rockwool panels on wooden frames are far better than just acoustic-grade foam of comparable density; they absorb a larger range of frequencies toward the bass end.
2. The thicker the panel, the more ample the bass-trapping capability of the panel.
3. Leaving a clearance of the same thickness as the panel you use between the panel and the wall will double the acoustic properties of such panel.

Right?

Here comes my question:

I have DIY panels of rockwool. They are 1.20m x 0.60m and 2" thick. If I stack two panels together and leave a clearance of 4" between the sandwiched panels and the wall, I'm getting four times the bass absorption of a single panel, being the whole structure 8" thick, right?

Please, shed some light on this.

All the best to you,

Carlos

 

2" rockwool (which one exactly?) is not nearly enough to really absorb bass frequencies. I don't know the dampening coefficient by heart but with Rockwool Sonorock I think you would need 250mm for 50 Hz absorbtion.
The best diy way to bass absorbtion are corner traps as described here:
http://www.radford.edu/~shelm/acoustics/bass-traps.html#BassTraps

 

It's a compacted panel that I bought from a heat insulation supplier. It's generic. I have a bass trap cylinder that goes floor to ceiling. Actually, the problem resonances and hard-to-tackle harmonics happen in the 300-600 Hz area, which I hope my panels can tackle sandwiched like I described before. Even if they don't reach that low, if they trap their multiple factor resonances, I'll ge getting something good going on. Right?

What do you think? The panels are already made. I have like 16 spares right now and the room measures 3.6 meters by 6m. The walls are not perfectly parallel, a lucky coincidence. Anyhow, if I stack two panels and leave a 4" clearance from the wall, we are not talking about 2" panels anymore but 8" panels, am I right?

 

Save rockwool for your hydroponic gardening. Auralex products are worth the extra expense, and they are fire retardant. If you don't use their products, their website has free tools and education. Or, just start putting your panels where your ears tell you. It's all good. http://www.auralex.com/

 

Hey mate.

I'm not an expert in this but with the panels I made, I put 8 in my studio and the bass got trapped big time, so I had to take a couple of them down (which later I put in my living room :D). I think it all depends on the size of the room, what type of floor you have, etc.

I am planning to use something similar to what Algae suggests for a vocal booth, but that one will be way down the line.

Oh, also I used something similar to rockwool, but they are actually acoustic insulation panels called "soundscreen", they're specifically designed for sound, not for blocking heat/cold. (http://www.soundscreen.com.au/)

 

cotton wall insulation you can buy at Lowes

 

But still rockwool is much better to absorb frequences then foam it is a well known fact

 

Absortion how thick rockwool do i need for that freq?

 

Has anyone actually tried helmholtz resonators for eliminating individual room resonances?
(actually, a properly calculated cabinet with a bass reflex tube)

If so, how do they differ from the above absorbers?

 

And where is the publication of this well known fact? Auralex does research on their products, and foam tiles are not the only products they offer. There are other brands and types of professional acoustic environment control products, also. Like this, for instance. https://www.gcaudio.com/cgi-bin/store/showProduct.cgi?id=666 How many professional studios use rockwool, egg cartons, generic foam, or all the other half assed measures I see mentioned here often, compared to how many use professional products designed for this purpose? if you can afford it, get the proper tools or supplies to do the job right, and save a lot do-over.

 

There is plenty of research on this topic.

The absorption coefficients for 5 cm mineral wool (40kg/m³, Rockwool Sonorock has 30-100 kg/m³) mounted to wall (example a), 5 cm mineral wool (40 kg/m³) 30cm in front of wall (example b) and polyurethane foam, 2.5 cm thick (example c) are:

A 0.15/125 Hz, 0.70/250 Hz, 0.60/500 Hz, 0.60/1000 Hz, 0.85/2000 Hz, 0.90/4000 Hz
B 0.70/125 Hz, 0.45/250 Hz, 0.65/500 Hz, 0.60/1000 Hz, 0.75/2000 Hz, 0.65/4000 Hz
C 0.16/125 Hz, 0.25/250 Hz, 0.45/500 Hz, 0.84/1000 Hz, 0.97/2000 Hz, 0.87/4000 Hz

1.00 would mean total absorption.

(Source: Cox & D'Antonio (2005) Acoustic Absorbers and Diffusers, Spon Press: London, Apendix A)

So the conclusion is that foam can achieve sound absorption comparable to rock wool. The thing is, even if specialized acoustic foam might get better absorption than rock wool, the heftier price tag eats up the advantage imho.
If I would treat my studio (which I don't because I know to judge the sound in here as it is and I'm sure I would just improve it for the worse), I would go for qrd diffusors and corner absorbers like this:

And, of course, if you want to do it right, measuring your room acoustically would be the unavoidable first step. Otherwise, every move you make is just fishing in murky waters.

If you need some literature on this I can recommend Shea/Everest "How to build a small budget recording studio from scratch". The book I posted above is more for you if you want to design absorbers yourself.

 

I found this retailer that specializes in sound control. Package deals, blemished items on sale, etc. Just in case somebody is interested. http://truesoundcontrol.com/clearance/?gclid=CJv2o-_si8MCFQ-OaQodplsA4Q

 

@Algae

I've noticed that you are very enthusiastic about Auralex products (I've seen you mentioning them in lots of posts). Please excuse this being a bit off-topic from the original post... what would you recommend as a good brand option for acoustic curtains? I may need one soon.

Cheers.

 

Demon-PM at you. Auralex not the only people with similar products, but they seem to know a little about the science of acoustics and treatment. My longterm experience for almost all tools is: if you can afford it, go pro the 1st time. "Why half ass a job when you can just go ahead and whole ass the thing."

 

Owens 703 insulation is where it's at.

 

Oh, and this might be helpful: http://ethanwiner.com/acoustics.html

 

I wouldn't think four times the absorbtion. But maybe 2 and a bit times. Cos it's an exponential factor at play the thicker you go. and the lower the frequencies.

If you know the frequencies you want to control i'd look at limp mass membrane absorbers. There's a formula to the size of the traps ands the frequencies they control (similar to helmholtz) only you can dampen them with foam or rockwool to widen the range as desired.

http://www.acousticsciences.com/art-noxon/limp-mass-membrane-bass-traps
https://www.gearslutz.com/board/bass-traps-acoustic-panels-foam-etc/743040-tims-limp-mass-bass-absorbers.html (download attachment from first post)

 

If you use Auralex you are gonna end up spending a TON more $$$ than if you just went the DIY route with some Rockwool/Owens/Knauff insulation. Do some research on Gearslutz in the acoustics section, there are hundreds of threads to read and get info from.