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acoustic sound absorption panels

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cello

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i reside in west bengal and im planning to have all the walls and the ceiling covered with some acoustic absoption panel. please advise
 

manu4panjab

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in my house..,
i reside in west bengal and im planning to have all the walls and the ceiling covered with some acoustic absoption panel. please advise

use simple bed foams that you can buy from that shop where you purchase all you bed mattress,cusions ,curtains,pillows etc etc

get foams in different size

1 inch for high frequency absorption

2 inch for mid frequency absorption

and 4 to 8 inch for bass traps
for your back wall use diffusers made from thick materials that don't absorb any sound like thermocoal,wood
 
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Hi-Fi

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If you want to build a simple working sound trap, build a thick mattress of the lowest density loose Rockwool. Rockwool is manufactured by Minwool Rock Fibers Ltd based in Hyderabad. There are also many other companies too, that manufacture rockwool.

The depth of the mattress should be slightly more than the size of the quarter wavelength of the lowest frequency you want to absorb. For example, if you want to absorb all the frequencies above 80Hz, the full wavelength of 80Hz is about 4.3m so the quarter wavelength is about 1.07m. A rockwool mattress that about 1.1m depth will absorb all frequencies above 80Hz.

Such traps are best located across the back wall of the room, that is the wall behind you when you are looking at your speakers.
 
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vaibhav

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Hi,
I did ask a dealer what he used in his demo room (they are rather well padded :)
He suggested buying glasswool rolls (for about 3.5K INR per roll), plus basic wooden frame and cloth of own choice (his suggestion was to use anything that doesnt absorb /retain moisture). With these, you should be able to build you panels.
I think the previous poster has referred to rockwool (which is probably the same thing) - then this would be the right way to go. Thickness is about 1 inch or more.
else you can use egg crates (ive seen it used when i was a broke student .. heheee)
cheers!
 
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manish26264

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Recently I have used 'CERA WOOL' for heat insulation, while inspecting the material I thought it could be used for sound absorption too, it is similar to glass wool but does not have itching property and is available in sheet form of size 1" / 2" thick, 24" width and 24' (foot) length.
Can we use gypsum board on the wall to absorb sound?
 
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Hi-Fi

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Rockwool is quite similar to Glasswool. However exposure to fine Glasswool fibers may be bad for health whilst Rockwool is considered safer
 
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Guns

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The depth of the mattress should be slightly more than the size of the quarter wavelength of the lowest frequency you want to absorb. For example, if you want to absorb all the frequencies above 80Hz, the full wavelength of 80Hz is about 4.3m so the quarter wavelength is about 1.07m. A rockwool mattress that about 1.1m depth will absorb all frequencies above 80Hz.

Hi, Sorry i didnt understand "A rockwool mattress that about 1.1m depth will absorb all frequencies above 80Hz." did you mean 1.1 meter depth or 1.1cm or 1.1inch depth.
 
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anm

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1 meter thick foam!!! where will I get it? I think there won't be any space left in my room for furniture if I sacrifice 2 meters of space in each dimension!
 
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Hi-Fi

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Perhaps this ideal room attached drawing will explain things more clearly. To calculate the quarter wavelength, take the speed of sound which is 343 meters per second and divide it by the frequency, which gives you the full wavelength. Then divide it by four to get the quarter wavelength

343 100 = 3.43 4 = 0.86 meter
343 90 = 3.81 4 = 0.95 meter
343 80 = 4.29 4 = 1.07 meter
343 70 = 4.90 4 = 1.23 meter
343 60 = 5.72 4 = 1.43 meter

So if you want to trap all the frequencies from 100Hz & above, the trap depth has to be more than 0.86 meter. If you want to trap all the frequencies above 60Hz, the trap depth has to be more than 1.43 meter ..... and so on. Its advisable to have a rear wall trap of 1.1 meter so that all the directional frequencies above 80Hz are totally kept under control.

Attached is a sketch of an ideal Reflection Free Zone (RFZ) also known as Controlled Image Design (CID) room. Notice how all the reflections are diverted into the rear bass trap and absorbed there. It is impractical to try and absorb the side wall reflections with massive traps. Whilst it is easy to put lots of absorption on the rear wall and perhaps even on the ceiling. This way the natural ambiance of the room is maintained keeping the side walls hard and bare. All the hard walls are non parallel, eliminating standing waves.

So building an ideal listening room is not that difficult if you have the space.
 
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venkatcr

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Its advisable to have a rear wall trap of 1.1 meter so that all the directional frequencies above 80Hz are totally kept under control.
So building an ideal listening room is not that difficult if you have the space.

Though this sounds idealistic, building a full wall bass trap that is nearly 4 feet thick is practically impossible. It may make more sense to build a full wall book case and line it with book for dispersion. Even hanging a thick curtain some 2 or 3 feet from the wall and using it only during music or movie session makes more sense. Rest of the time the curtains can be drawn back to make the place look better.

It will be easier and (maybe less expensive) to build small absorption boards and hang then on the parallel walls, as well as build floor to ceiling bass traps on two corners.

Cheers
 
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Surrealistix

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You should consider using Rigid Glass wool Boards of 48kg/m3 density for first reflection points on the walls and ceiling and 96kg/m3 mineral wool for bass traps.

The RFB came in a box with 8 boards each measuring 3 feet by 4 feet and 2 inches thick and costs around Rs. 1200. I doubled these boards to get 4 inches of thickness for the boards placed against the wall and 6 inch thickness for the ceiling trap. Remember to maintain a couple of inches of air gap between the wall and the panel. I have a 6 inch air gap on the ceiling panel.

For the corner traps I used 2 inches of RFB backed by 4 inches of Mineral wool to make it 6 inches thick.

I found the ceiling trap to make the biggest difference in sound.

The corner traps helped my room to a small extent as low as 100 Hz, but I found that careful subwoofer placement is more effective between 35 to 120 Hz.

The RFB boards cost me about Rs. 1200 for a box of 8 boards.
Mineral wool was cheaper.

Acoustics is tricky business - spend a lot of time reading about it on the Internet before you do anything or just buy a box of these boards and try it out :)

I hope this helps.
 
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reju

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Hi there,

I need to make sound absorbtion panels, to cover 60% wall and 50% ceiling of room 35' x 20'

So I was considering softboard (12mm) + fibre glass wool (16kg/m3) covered with felt wool cloth. In panel sizes of 4'x2' and placing them with a gap of 1 foot from each other.

Now I have heard about Rigid Glass wool Boards 48kg/m3. Can this be used directly with wool cloth cover or the base softboard (Jolly board) is still required?

Thanks for your inputs.
 
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jls001

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So building an ideal listening room is not that difficult if you have the space.

Hi Hi-Fi,
What you wrote is the scientific principles and the scientific solution. There's no arguing with that:)

Now, do tell us the engineering solution to the problem. By engineering solution I mean something that is do-able, yes, a compromise from the ideal, but a solution for about 95% of the problem, while retaining the floor space and room aesthetics (and not being thrown out by partners/wives/rest of the family:lol:). Many of us use our living rooms as listening room and sacrificing 0.86 meter (2.82 feet!) of rear wall is impractical.
Joshua
 
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pdhanwada

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I dont think 25% of wave length is not need for flat absorbtion. Please read the following post. It can be even 3.5% of the wavelength to get that frequency absorbed.


AVARE writes in gearslutz.com

Q 4 Avare - Gearslutz.com

Thanks Dan. You hit the nail on the head, or rather identified exactly the point that has been holding me back on the article about gas flow resistivity. Specifically the effect of gaps between porous absorbers and reflective surfaces. I have not been able to determine the best manner in which to explain the effect and that gaps greater than the thickness of the porous material provide flat absorption.

There. I wrote the important thing. Now I just thave to expain it in an effective manner.
In the following explanation I will try to work from the basics in a way that other readers can hopefully understand the priniciples involved also.

The classic way that the effect of gaps is explained is by use of graphs of thin absorbent material spaced away from a wall. The graphs show high values of ? where the distance from the wall is 1/4 wavelength and 0 when the wavelength is 1/2. In other words the porous material is effective only where the particle velocity is high. These graphs are appropriate for thin material. The porous materials that we consider when discussing the use of gaps are not thin at the wavelengths significant to us. Therefore the graph is not accurate for our use of gapping!

Gapping is used to lower the effective frequencies of the sound absorption. It is usefull to start with the effect of thickness of homogenous porus material against a solid surface. This the mounting of material used in the reporting of the absorption of materials as used traditionally in studios. With typical porous material, using 703 for the example, at 4" thickness, ? is 1 down to ~250 Hz and usually considered effective down to ~125 Hz. At 250 Hz the wavelength is 4.52 feet. Dividing the thickness of the material by the wavelength (.333/4.52)gives us a ratio of .0737, or ~7%. So the thickness of a porus absorber has to be at least 7% of the wavelength for flat absorption. If we consider 703 material absorption at 125HZ to be practically 1, this gives a ratio of 3.5%.
Remember, the previous paragraph deals porous material against a solid surface. This is the area where the particle velocity is lowest in the sound wave. The efectiveness of a non thin absorber is not significantly reduced when located in the relatively low region of particle velocity.

Having shown what the depth of a porous absorber has to be in order to be effective, this leaves the question of the required material depth to gap ratio for effective absorption. This is not as clear as the overall depth calculation due the physics involved and some other non-intuitive factors. The usual belief is that the path of sound sound through an absorber is straight through the material. This is also named the normal incidence. However when sound impinges on an absorber at a non normal angle, the path is greater. The significance of this is a reduction, up to a complete removal, of the point on the thin absorber graph where no absorption occurrs.

When sound travels in air, it doing so in an isothermal manner. That is that at the points where the presuure increases, and the temperature (the combined gas law), the additional heat remains that area. That is, there is movement of the energy in the sound wave. In porous material, the material conducts the heat away from the ares of high temperature to areas of lower temperature.

This is called adiabatic. The ratio of the square root of specific heats of air for constant volume vs constant pressure is the same as the ratio of the speeds of sound in air when traveling isothermally vs. adiabatically. The effect is that that porous absorbers behave with effective thicknesses ~120% greater than the physical depth. The practical result is that for acoustic matching to the peak velocity of a sound wave and covering the full 1/4 cycle, the depth of the gap is 1.2 times the depth of the depth of material.

There is of course the variable sound path length from the various angles of incidence also. So the true effective depth for a gapped porous absorber is more than 1.2 times the material thickness. This leads to the question of how much more? In acoustics, we have the ultimate arbiter of test data. Gapped porous absorbers are used in thousands of spaces with gap to depth ratios up to 20:1. These absorber systems are called acoustic ceilings. This sort of mounting is calld E-405. It consists of absorbent material suspended 405 mm (16") away from a solid surface. The acoustic tiles are as thin as ~20 mm(3/4"). Studying test data on such mounted materials does not show any dip at the 1/2 wavelength frequency implied by the thin absorber graph.

An example of a purpose built absorber using a 2:1 gapping ratio is in the Heinieken Music Hall, construction details in fig 5 in Acoustics for Large Scale Indoor Pop Events. There is an internationally recognized studio designer, who in the process of designing a wolrd class facility did testing on gaps and used gap to material ratios of up 2.2:1. He is a rather quiet person regarding his work and out of respect for him, I am not disclosing his name or the studio.

The point to answer your question, is no, 1:1 is not a limiting ratio for gap to absorbent material ratios. Ratios up to 20:1 are used regularly in non-critical acoustic spaces, and ~2:1 for critical acoustic spaces, including studios.

I hope this helps with the ostensible question. Reaction to this post and thread and this post will help me compose the major piece on soound absorption and porous absorbers. You got me started in getting past the stumbling block Dan.

Well spaced,
Andre
__________________
Good studio building is 90% design and 10% construction.
 
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raghumailbox

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Hi there,

So I was considering softboard (12mm) + fibre glass wool (16kg/m3) covered with felt wool cloth. In panel sizes of 4'x2' and placing them with a gap of 1 foot from each other.

Try Anutone's Subtex panels which is available from 15mm to 25mm thickness and it is light weight.

Anutone has N number of products for acoustical solutions.
Anutone - makes you feel good
 
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harkoc

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Should I buy rockwool or GlassWool for sound absorption ? Please suggest.I am very Confused .
 
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sdurani

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Glasswool is essentially fibreglass, which is annoying to work with (makes your skin itch) and unhealthy to breathe. Much easier to work with Rockwool.
 
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