Question for Ethan and all other pros.

[Graal]

Hello Ethan!

I would like to start off by saying that I admire your work and you as a person (from what I've seen and read).
I love the fact that you always try to help people and debunk myths.

I, myself, am always an advocate for Acoustics as top priority before more and more gear.

If I may, I would like for you to help me understand the following better:

I want to build some acoustic panels for a club.
The club will also have a small stage, 10' x 8', for bands.
I want to use rockwool (I hope this is the corect term for mineral wool made from volcanic rock - bazalt)

I understand that rockwool is somehow slightly better than glass fiber wool, right?

What density do you think I should go for?
What is the real norm/theory behind one's choice?

Up until now I thought that denser might be better. I think these were your thoughts too, in those tests you made.
But how dense?

I thought about using 100mm thick (2 x 2") rockwool that has a density of 135 Kg/m3 or 150 Kg/m3.

But then looked at some charts today and different absorption coefficients.
http://www.bobgolds.com/AbsorptionCoefficients.htm

After that I thought 135 Kg/m3 or 150 Kg/m3 might be overly excessive.

From what I saw, I reckon I should use 4" (2x2") thick insulation with a density of between 48 Kg/m3 and 72 Kg/m3 for the best broadband absorption and bass trapping.

What do you think?

And should I space the panels from the walls or not?

How do you feel about triangle corner bass traps as opposed to panel corner bass traps(that leave air between them and the corner)?


Thank you for your time,
I really appreciate it!


Alex.

[Graal]

PS: About your mineral wool density and frk test.
Rigid fiberglass density tests

Do you think the result would have been different, say you had the same number of 6" panels as you had for the 3" ones - i.e. 12?
Because, in the test, the upper side of the corners remained untreated.

[Ethan Winer]

The general recommendation for rock wool density is between 40 and 100 kgm3. Higher density might be okay. I honestly don't know because I've never measured or compared material that dense.

Rock wool that's four inches thick should be very good. Adding an air gap can only help, though it's more difficult to attach the panels to the walls. You'll need to come up with a way to hang the panels with a gap. For panels four inches thick I'd use a gap of 2 to 6 inches, with the larger gap size being better.

Filling a corner solid is better than a four-inch panel straddling the same corner. But it's only a little better, and uses three times more material. So if cost is not a concern, go ahead and fill the corners. Otherwise you're better off using the same amount of material to have more 4-inch thick panels.

--Ethan

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The Acoustic Treatment Experts

[Graal]

Another question, if you don't mind...for my room at home this time.


Do you consider that at first reflection points, a 24"x48" - 4" thick panel would suffice or should i double that and make it a square 48"x48" panel?

Any other suggestions?


One other thing:

If I alternate panel thickness in the room (2",4",6",8") to make away with simetry, would it make a difference?



PS: My room is aproximately 18' x 13' x 8.5'.

Thanks!

[Glenn Kuras]

Do you consider that at first reflection points, a 24"x48" - 4" thick panel would suffice or should i double that and make it a square 48"x48" panel?

24"x48" area is fine, but I always recommend larger when possible. When mixing you may move your head around so covering more area on the sides (and ceiling) will widen the zone.

[Glenn Kuras]

If I alternate panel thickness in the room (2",4",6",8") to make away with simetry, would it make a difference?

I would recommend using the same thickness when it comes to the early reflection points on the side walls.

[nosebleedaudio]

Originally Posted by Graal

Another question, if you don't mind...for my room at home this time.


Do you consider that at first reflection points, a 24"x48" - 4" thick panel would suffice or should i double that and make it a square 48"x48" panel?

Any other suggestions?


One other thing:

If I alternate panel thickness in the room (2",4",6",8") to make away with simetry, would it make a difference?



PS: My room is aproximately 18' x 13' x 8.5'.

Thanks!

I would go at least 48" by 48"..for ALL first reflection..
I prefer more like 60" high and 5 to 6 feet wide for the side walls in a room that is that size. IF you are using it 18' length wise..IMHO..

[Ethan Winer]

Originally Posted by Graal

Do you consider that at first reflection points, a 24"x48" - 4" thick panel would suffice or should i double that and make it a square 48"x48" panel? ... PS: My room is aproximately 18' x 13' x 8.5'.

Reflection "points" are not really points but areas. In a room 18 feet long you may be far enough away from the speakers that 4x4 feet is needed. Or even larger as Mike suggested. Better too large than too small.

--Ethan

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The Acoustic Treatment Experts

[Graal]

Another Question:

Where does the limp mass membrane go?

In front of the panel (toward the room) or on the back (toward the wall) or how about on both sides?

Does the limp mass membrane need to be spaced 1-2 inches or more from the panel? Does it hang freely or can you attach it on 2 or all 4 sides?


Thank you a bunch!

Alex.

[Ethan Winer]

The membranes I've used are similar to the FRK paper that comes bonded to rigid fiberglass. You can either just buy FRK fiberglass and be done with it, or spray-glue your own paper or thin plastic onto the front surface that faces the room.

--Ethan

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The Acoustic Treatment Experts