Shape of Studio

[FLZapped]

Originally Posted by Mike Sommer

There are only two things that kill sound: mass and distance.

That's why 703 Rockwool and high density cellulose batts trap and control sound. Look at OC's data sheets.

The fluffy batts are full of air, which is good for insulating from heat and cold, and 703 is not.

Fluffy batts will knock out some frequencies, but not the wide range we are looking for here.

You're wrong. R-19 has an absorption coefficient of 0.64 at 125Hz, 1.14 at 250Hz, and an NRC of 1.04. The use of faced R-19 and put the paper out and it jumps to 0.94 at 125Hz, but you loose some on the high end. Standard 2" 703 is 0.17 at 125Hz, 0.86 at 250Hz, and has an NRC of 1.0.

Even unfaced R8 is better at 125Hz, although 2" 703 exceeds it after that point, but it just shows that you cannot dismiss standard fiberglass insulation.

If you only have 2" to work with, 703 is the way to go. But if you're looking at stuffing some of those rafters, which appear to be at least 6" deep, standard insulation will work great and save you money.

-Bruce

[Mike Sommer]

Yes the fluffy stuff does control low frequency velocity, but that's all it does for the most part. My comment -though I should been more descriptive- was only addressing the confines of controlling a broad spectrum of frequencies. Where as with proper understanding of 703 or other high density materials, effective and efficient installations can be achieved.

Understanding the entire Absorption Coefficients Chart is most important.
Realize those numbers for 703 are for a 'Type "A" Mounting' -directly on the wall. With 2" of 703 with an air gap between wall, an absorption coefficient of 0.65 @ 125Hz, 1.01 @ 250Hz is achived. The larger the air space the more effective the 703 becomes at controlling bass. Mass and Distance effectively controlling low frequencies, or controlling sound by controlling its velocity.

So if he stuffs 6" of 703, with a 4" or larger air gap, he will effectively control bass build up along that ceiling, if he really wanted to go crazy stuffing the entire ceiling joist will eliminate any and all problems.

Then again bass does not tend build up along the ceiling, bass builds up in the rooms corners, which is why I recommended bass traps there. Also holding off 4" of 703, 2 to 4 inches from the wall will effectively control sound at and above low frequencies. Also a bass trap can be installed along one of the shirt walls, by building a frame 16" to 24" from wall and install 4 to 6 inches or 703. Bass in that room should be effectively controlled in that room.

All this noted without sound measurements being made or the total room dynamics understood.

[FLZapped]

Originally Posted by Mike Sommer

Yes the fluffy stuff does control low frequency velocity, but that's all it does for the most part.

Understanding the entire Absorption Coefficients Chart is most important.
Realize those numbers for 703 are for a 'Type "A" Mounting' -directly on the wall. With 2" of 703 with an air gap between wall, an absorption coefficient of 0.65 @ 125Hz, 1.01 @ 250Hz is achived. The larger the air space the more effective the 703 becomes at controlling bass. Mass and Distance effectively controlling low frequencies, or controlling sound by controlling its velocity.

OK, so lets look at the numbers as provided by Bob Gold:

table.doc

So, looks like the whole mass thingy doesn't work out so well here. And it also appears as though good ol' fluffy fiberglass IS effective across a broad frequency spectrum.


-Bruce

[Mike Sommer]

That would be 6.25 inches vs 2 inches of material. Yes it would seem the denser 703 is performing better, and better yet when you compare 6 inches of 703 to 6 inches of batt fiberglass fluff.



After crunching some numbers, I will concede that the stuffing the ceiling joist with fluffy batts can and would be a real option. Now find 20" batts

[edwinoldfield]

Looking at the chart from Bob Gold. when it says in the air, versus on the wall. What does this refer to? Is that a space of 16 inches between the insulationn and the wall behind the insulation versus directly on the wall. I know leaving a space has been mentioned in this post but is it 16 inches in the chart? I know the leaving of space between the insulation and the barrier/wall behind it has been mentioned. If I understand these figures in a pedestrian way the greater the number the more the absorbtion.

[Mike Sommer]

Yes the reference is 16 inches, between the wall and fiberglass, I think the wall is plywood in the reference model.

Distance from the wall increases the the efficiencies of the lower frequencies control. What happens is, low frequencies pass through the 703, reflects off the wall and back into the 703; distance and mass controlling low frequencies. Another factor of the control of bass is the finish wall material. Walls made of gypsum are a very effective bass controller, these walls act as a sort of membrane absorber. Which leads me to the question what is the finish of your interior walls, plaster or drywall?


But understand that bass builds up in the corners, i.e. the corners where two walls come together, a floor and wall or the ceiling and wall. So for your needs, building a floor to ceiling bass trap, 6" thick, 2' wide, will effectively controlled the build up of bass. The golden-orange panels in this illustration below, show how they are set. (You can also fill the backs of these bass traps with scrap insulations for better control)

I also suggested building a "bass trap wall" (yellow trap in pic) along one of the short walls, six inches thick, and 16 to 20 inches from the wall. This may be total overkill but it will suck out a lot of bass. But I would not do this unless you are having real problems.


Your best bet for broad band frequency control would be to use 703 floor to ceiling, along the length of one of the long walls and the two shorter walls; Two or four inches of 703, with an air space of about two to four inches between the 703 and the wall. This will just about kill just about all the refections in this room. You will need to do something with the second long wall. Either cover the second long wall with 703 like the other -this might be best- depending the finish of this wall material, and how the room sounds. Or you can install 4" 2x4 or 2x8 panels along the wall.


Here is a fabric a lot of people use:
http://www.soundaway.com/acoustic_fabric_p/21005.htm

[FLZapped]

Originally Posted by Mike Sommer

That would be 6.25 inches vs 2 inches of material. Yes it would seem the denser 703 is performing better, and better yet when you compare 6 inches of 703 to 6 inches of batt fiberglass fluff.

R8, which is 2.5", was also included and is is pretty close. However, the examples used were for the most commonly available materials.

There are a couple different things here that need to be differentiated.

1) Transmission loss
2) Absorption


For transmission loss, there is no doubt that using 703, or even 705, in a wall cavity is superior to regular fiberglass. Here, the mass equation works every time.

In terms of absorption, the depth of the absorber has as much effect as the material used. There is also an edge effect that comes into play which makes the absorber seem to be larger than it is. So it is possible to save some money here and use the lesser expensive fiberglass insulation.

As for modes, they all terminate in the corners, so a proper broadband corner trap will be effective for all room modes. However, it must be done right - which means it should be as big as one can possibly make it and it needs to seal against the walls and the floor and the ceiling to be maximally effective.

In the example we have here, the room is a long rectangle, so additional absorbers will be needed to control echos along the four parallel surfaces. (Don't forget the ceiling and floor) Usually about 40% coverage is all that is required.

Careful placement can not only control echos, but also help tamp down modal responses.

-Bruce

[FLZapped]

Originally Posted by Mike Sommer

I also suggested building a "bass trap wall" (yellow trap in pic) along one of the short walls, six inches thick, and 16 to 20 inches from the wall. This may be total overkill but it will suck out a lot of bass. But I would not do this unless you are having real problems.

This is not really needed. Another set of corner traps will be sufficient. If more traps are needed, sure add them, but covering the whole wall uses more material than needed. One can take advantage of the edge effect of individual traps which makes them seem larger than they physically are and save on material.

As for the speaker end of the room, you need to create a Reflection Free Zone (RFZ) so placement of the absorbers will need to align with the first reflection point on the walls. EDIT: Need to add, that includes the ceiling, too.

-Bruce

[FLZapped]

Originally Posted by Mike Sommer

That would be 6.25 inches vs 2 inches of material. Yes it would seem the denser 703 is performing better, and better yet when you compare 6 inches of 703 to 6 inches of batt fiberglass fluff.

R8, which is 2.5", was also included and is is pretty close.

There are a couple different things here that need to be differentiated.

1) Transmission loss
2) Absorption


For transmission loss, there is no doubt that using 703, or even 705, in a wall cavity is superior to regular fiberglass. Here, the mass equation works every time.

In terms of absorption, the depth of the absorber has as much effect as the material used. There is also an edge effect that comes into play which makes the absorber seem to be larger than it is. So it is possible to save some money here and use the lesser expensive fiberglass insulation.

As for modes, they all terminate in the corners, so a proper broadband corner trap will be effective for all room modes. However, it must be done right - which means it should be as big as one can possibly make it and it needs to seal against the walls and the floor and the ceiling to be maximally effective.

In the example we have here, the room is a long rectangle, so additional absorbers will be needed to control echos along the four parallel surfaces. (Don't forget the ceiling and floor) Usually about 40% coverage is all that is required.

Careful placement can not only control echos, but also help tamp down modal responses.

-Bruce