Are 12-inch panels an overkill for just a voice recording studio?

[themylogin]

I am planning to build some acoustic absorption panels to treat the room where I will be recording my speaking voice. Using the Porous Absorber Calculator (http://www.acousticmodelling.com/porous.php) suggests that to achieve an absorption coefficient of 0.7 at 100 Hz, I need a 12-inch panel consisting of 6 inches of 5000 rayls/m Rockwool and a 6-inch air gap.

However, most of the ready-made products are 4-inch panels (6-inch at most) designed to be installed directly on the wall. Inputting their parameters into the calculator yields significantly inferior performance: almost no absorption at 100 Hz and mediocre absorption at 200-500 Hz (aren't these the frequencies responsible for a "boxy" voice sound?)

Blue line is the 12" panel I think I need, green line is the 4" panel they sell, claiming it'll be sufficient.

Am I missing something, or is 0.4 absorption at 200 Hz enough? Or 4-inch panels are merely well-marketed room decorations, and I really need to build giant 12-inch panels? My room dimensions are (L x W x H) 352 x 252 x 274 cm.

 

[Folkcafe]

Coefficients below .75 are pretty much ineffective. 2.4m is about the wavelenth of aprox 200hz. (Rough guess, check my math) Cube room you'll have that in 3 axis'. 1/2 wavelenth 100hz and 1/4 50hz.

Male Frequency range is 85-180 typical. Female 165-255hz.

My first question is where did you get that air flow resistivity ratings from? Rockwool would be much higher.

I'd first start with some accurate measurements of the space then calculate out the modes. Then figure out what insulation products are available to you, then I can help you find accurate numbers on resistivity.

No matter what, you'll likely have to play with mic placement in this space to find just the right spot and height that is just between null and node.

 

[themylogin]

My first question is where did you get that air flow resistivity ratings from? Rockwool would be much higher.

Sonorock Eco datasheet suggests > 5 KPa · s/m2 https://www.diaterm.com/wp-content/uploads/2019/07/FT_Sonorock-Eco_ES.pdf

We also have Alpharock 225 which is > 20 KPa · s/m2 https://www.diaterm.com/wp-content/uploads/2019/07/FT_Alpharock-Premium_ES.pdf

I can probably find something in-between. There also panels like https://www.don-audio.com/CARUSO-ISO-BOND-WLG-040-100mm-Akustikvlies-Schallabsorber_3 that are 3000, 5000 or 10000.

I'd first start with some accurate measurements of the space then calculate out the modes. Then figure out what insulation products are available to you, then I can help you find accurate numbers on resistivity.

Thank you! Actually, my original message was incorrect. The room dimensions are (L x W x H) 352 x 252 x 274 cm.

 

[Folkcafe]

Sonorock Eco datasheet suggests > 5 KPa · s/m2 https://www.diaterm.com/wp-content/uploads/2019/07/FT_Sonorock-Eco_ES.pdf

We also have Alpharock 225 which is > 20 KPa · s/m2 https://www.diaterm.com/wp-content/uploads/2019/07/FT_Alpharock-Premium_ES.pdf

I can probably find something in-between. There also panels like https://www.don-audio.com/CARUSO-ISO-BOND-WLG-040-100mm-Akustikvlies-Schallabsorber_3 that are 3000, 5000 or 10000.

Thank you! Actually, my original message was incorrect. The room dimensions are (L x W x H) 352 x 252 x 274 cm.

I found a reference listing about 6k so pretty low density product compared to some of the product regionally avaible where I live (cold climate)

Picking material for this is about finding what works best out of what you can get. The problem, as you might be aware, is that as the densitiy goes higher, so does the effective thickness at low frequencies. Run the calculator numbers from 3000 to 15k at various thicknesses and see what I mean. It will graph out what I am saying.

Good luck finding the most effective product at a reasonable thickness. It seems like you are on the right track.

If this was a new build, I'd suggest using double wallboard on the outside and skipping it on the inside. just cover the inside with fabric and make the entire space absorptive.

 

[rob aylestone]

I love these ‘rules’. Heavy on the science, light on common sense. Imagine you have EQ with a cut/boost knob scaled -10 through to +10, but your mixer has a dodgy knob that only allows -5 to +5, you'd still cope. 12” is great, but few people have the money or space, and 3” seems very common as it fits inside commonly used timber, or typical cavities. Before building my past studios i read as much as i could and came to the conclusion that in almost every area i had to compromise for cost, physical but often skill reasons. One i built in the 90s was built in a bigger space than i needed, allowing people to walk around the gap between studio and building. There was the inside structure, then the gap and then the outside freestanding frame as usual but them two feet till the building brickwork. We decided to use this wasted space for storage, so added an outside skin of plasterboard to make it people proof. The figures tell you what reduction in transmission you get, in and out. It was undetectable to us, but clearly it did something. We just couldn't detect it.

 

[Folkcafe]

I love these ‘rules’. Heavy on the science, light on common sense. Imagine you have EQ with a cut/boost knob scaled -10 through to +10, but your mixer has a dodgy knob that only allows -5 to +5, you'd still cope. 12” is great, but few people have the money or space, and 3” seems very common as it fits inside commonly used timber, or typical cavities. Before building my past studios i read as much as i could and came to the conclusion that in almost every area i had to compromise for cost, physical but often skill reasons. One i built in the 90s was built in a bigger space than i needed, allowing people to walk around the gap between studio and building. There was the inside structure, then the gap and then the outside freestanding frame as usual but them two feet till the building brickwork. We decided to use this wasted space for storage, so added an outside skin of plasterboard to make it people proof. The figures tell you what reduction in transmission you get, in and out. It was undetectable to us, but clearly it did something. We just couldn't detect it.

I had thought to add to my post that Rob would be along any moment to let me know I am wrong. I don't know where I lacked "common sense" but I answered the questions as presented with some practical advice. Yes, even backed by a bit of heavy science. When I took all those courses in acoustics and audio measurement, I didn't see any courses available in that illusive branch of science called "common sense". Acoustics is among the least intuitive branch of science. It's an area where common sense doesn't get you far.

This is where my issue with your comment stems from. I didn't comment nor did I address any of the above. I do know that vocal booths are among one of the most difficult types of rooms to make sound natural. The OP is looking to fabricate some absorption panels. In doing so, there is often a range of products to pick from. There is the old adage, any job worth doing, is worth doing right. I offered advice on where the product he had considered would be effective and detailed the frequencies he needs to treat for vocals wouldn't be covered effectively by those panels. I even took the time to look at the spec sheets and run some numbers. Sometimes when attempting to treat a problem area, you inadvertently treat the frequencies above it which only serves, to increase the ratio of the problem frequencies to the rest. Now those frequencies are spot lit.

As to EQ, it will require the fundamental along with all the relative nodes. So your advice is going to be to high pass 50hz, then EQ 100, 200 & a bit of 400hz?

In the 70's most of the local studios I recorded in were really bad. I'm talking the types of old rooms with egg cartons on the walls bad. We learned all about mic and source placement as a workaround. Problem is this solution is a lot more difficult in a 7ft room.

In these types of posts, I advocate first understanding the problem then analyzing the effectiveness of the proposed solutions. I'm certainly not in the "any treatment is better than no treatment" camp. I've read too many "I treated my room now it sounds worse" posts on studio building forums where someone has poorly treated a room only to highlight bigger issues.

Don't get me wrong, I have a great deal of respect for you and value your opinions generally. It's just that you seem to have this odd bias in these types of posts. I've read enough of them over the years. It would certainly be worth a discussion.