# Need help with Acoustic Panel Construction



## gskinusa (Dec 21, 2008)

Hi
I got 4 boxes (4 sheets each box) of 2in by 4 ft 8lb Mineral wool that I thought would be useful for building some acoustic panels for the theater room. The room is 20ft lenth, 9ft 8in width and 9ft height. I have an AT screen 106" diagonal (16:9) around 4 ft from the wall and the front Left and Right speakers are behind the screen. The Center is little below the screen and the subwoofer is next to the right speaker close to the wall. The surround and surround back speakers are around 7ft heigh. My first viewing distance is around 11ft from the screen and the 2nd one is around 15 ft from the screen. The projector is at this time is shelf mount at around 17ft from the screen. The basic structure is like below. For details you can see the photos in the following website My Home Theater

----Window----
|....screen......|
|...................|
|...................|
|...................|
|...................|
|..1st seating..|
|..2nd seating..|
\...................|
\__________ |
Door


My thought is to have the left and right corner with a panel that will be 8ft tall and 2 ft wide. Then have 3 panels on each wall each 8ft by 2ft. In the back wall have a 3ft by 4 ft panel hung on the wall. Now the questions I have are:
Am I moving in the right direction to improve the sound.
Will the 8lb 2 in wool be a good bass trap. 
Do I need to cut the wool in to half vertically to make it 1in thickness so that I can use it for the left and right panel for absorption to reduce reflection or I can use it as it is even for that use. 

Can you please help me with the answers for these questions. Please let me know if you need additional information.

Thank you


----------



## bpape (Sep 14, 2006)

The 2" will be OK for reflection panels though the density is a bit high for this application.

For the corners and the rear wall where you're concerned more with bass, I'd go at least 4" thick. I'd also straddle the front corners instead of going flat on the wall to extend how low they'll be effective.

One other suggestion, your primary seating position is way too close to the middle of the room. You're sitting in a lot of bass problems from the room length. Try sitting 12.5-13' from the front wall to your seated ear position to help smooth things out.

You'll still want bass absorption from a decay time standpoint - just trying to get you into a better overall position for bass response from the start. One of the few 'free' things in this hobby of ours.

Bryan


----------



## gskinusa (Dec 21, 2008)

Hi Bryan
Thank you for the quick reply and suggestions. Regarding the seating area I will definetly try to move the seating to 12 to 13 feet. 

For the corner bass traps, so based on what you are saying should I stack 2 sheets together and still keep the height to 8ft (that means use 4 panels for each side) or just have a 4 ft tall panel on each corner with 4" thickness (2 sheets stacked). Please let me know.

Regarding the reflection panels, I too felt that 8lb may be little high but had to go for that as it was only available in bulk. Do you think I can cut that vertically in to half so it will 1". Does it help or that is no better or worse than having the 2" intact and use it as it is?

Thanks


----------



## bpape (Sep 14, 2006)

Cutting it into 1" thick is going to be basically impossible. It also doesn't impact the density. Density is purely weight per cubic unit.

For the corners, yes, double the thickness. This will extend how low they will function. However, this does not change the need for pure square footage. Haivng 4' instead of 8' and 4" instead of 2" will reach lower but with half the overall absorption exposed to the room.

Bryan


----------



## gskinusa (Dec 21, 2008)

Got it. Thank you. I will try your suggestions and will come back if I have few more questions.
Thanks
-Senthil


----------



## waldo563 (Apr 26, 2009)

gskinusa,

Have you considered "Superchunks" for the corner absorption where the material is cut into right triangles and stacked in the corner? I am not a technical expert on this but I believe that with this method you could get away with a smaller frontal area due to the fact that the material fills in all the way into the corner and so is less obtrusive. One potential pitfall may be the use of mineral wool which is probably much harder to cut into the multiple smaller pieces. I have not personally mineral wool but the rigid fiberglass insulation that I used was very easy to cut using an electric knife.


----------



## bpape (Sep 14, 2006)

Chunk absorbers are great and do take up less space. To do the same frontal area in chunks (17x17x24" triangles) takes the same amount as 6" of thickness straddling a corner.

Again, reducing the frontal surface area exposed to the room will reduce overall bass control, though the chunks will reach deeper. You just can't cheat surface area. I could make something 30 FEET thick and if it's 1/2 the surface area, it's 1/2 as much bass control.

Bryan


----------



## gskinusa (Dec 21, 2008)

waldo563 said:


> gskinusa,
> 
> Have you considered "Superchunks" for the corner absorption where the material is cut into right triangles and stacked in the corner? I am not a technical expert on this but I believe that with this method you could get away with a smaller frontal area due to the fact that the material fills in all the way into the corner and so is less obtrusive. One potential pitfall may be the use of mineral wool which is probably much harder to cut into the multiple smaller pieces. I have not personally mineral wool but the rigid fiberglass insulation that I used was very easy to cut using an electric knife.





bpape said:


> Chunk absorbers are great and do take up less space. To do the same frontal area in chunks (17x17x24" triangles) takes the same amount as 6" of thickness straddling a corner.
> 
> Again, reducing the frontal surface area exposed to the room will reduce overall bass control, though the chunks will reach deeper. You just can't cheat surface area. I could make something 30 FEET thick and if it's 1/2 the surface area, it's 1/2 as much bass control.
> 
> Bryan



Thank you for your suggestions. Unfortunately I am limited in budget and trying to work with the mineral wool that already have. By the way from the look of it, I think it can be cut in to a triangle but I am not sure whether I want to do that as anyway this will be hidden behind the screen. Is my thought correct?. I am thinking of having the panel reach a size of 8ft high, 4" thick and 2 ft wide. This means I will be using 8 of the 16 sheets I have for the corner bass trap (left and right). So I will be left with only 8 to use them as reflection panels. I was thinking I will do two 8' high, 2" thick, 2 ft wide panels on each wall (right and left). Previously I was thinking of doing 3 panels each wall. Do you think it is ok or should I reduce the height of the panels to be 4' that way I can do 4 panels on each wall horizontally instead of 2 vertically. Please let me know.

Thanks again for the suggestions.

-Senthil


----------



## bpape (Sep 14, 2006)

On the side walls, you don't need to go 8' tall. Just using 2x4 panels, likely 3 each wall will be plenty.

If you do 12x12x17 chunks, you can get 16 triangles (32") from each 2'x4' piece. Not as much surface area but it works within what you have and is a more balanced solution.

Bryan


----------

