martes, 18 de diciembre de 2012

Difference between acoustic absorption and sound insulation

Estos dos conceptos son utilizados indistintamente cuando no debería ser así.

In this post we will try to clarify these concepts and move them to everyday situations to help understand them better.

We begin with the sound absorption, this is a property that present all materials which absorb part of the acoustic energy index on them in the form of sound pressure waves, transforming it into other forms of energy (usually heat).

The following graph (obtained courtesy of World of acoustic) illustrates these concepts, part of the incident energy (Ei) is reflected (Er), another part is absorbed by the material (Ea) and some is transmitted (Et), fulfilling provided that Ei = Ea + Er + Et



Most of the materials identified with the label "absorbent material" acoustic property should this entrapped air within as small cells. The acoustic energy is converted to heat energy due to rubbing. The advantage of such materials is that their good properties as combine sound absorbers with a reduced weight due to its greater part are formed by air. Examples of such materials are rock wool and glass widely used in construction.

The manufacturers of absorbent materials apport the absorption coefficient curves in function of the frequency of the incident sound wave, ls usual values ​​of the absorption coefficient is in the order of 0.9 to 0.95 for medium and high frequencies. This means that 90% of the incident acoustic energy is dissipated by the material in this frequency range.

Although acoustic absorbing materials dissipate a high percentage of incident sound energy by themselves do not solve the problems of acoustic isolation

Sometimes absorbent materials are attached directly to the walls of the enclosures to be treated, this treatment improves acoustics barely inside the premises diminishing its reverb but does not improve the sound insulation of the fences. This is due to the nonlinear nature of the sound.

But what does it mean to "non-linear"?, I will try to explain as clearly as possible with an example. If you have a stereo emitting a sound level of 60 dB and bring another team to 60 dB emitting identical the result will be 120 dB (thank God) but will have only 63 dB.

If the same thing happens absorbent materials, dissipating much energy even fail to dissipate enough to get rid of the noise transmitted to the trouble (just cut a few decibels of noise incident).

Absorbent materials are useful in architectural acoustics, but as we will see always in combination with other materials.

With regard to acoustic insulation property is presented a material or set of materials that form a closure to prevent the sound passing through ensuring the comfort across the enclosure in which sound is generated.
The mechanism of action is as follows: part of incident sound wave is reflected by the material while another portion thereof is irradiated by the material in the form of vibration, this vibration causes starts moving the air in the side material opposite the sound. A fraction of the energy that is dissipated through the material.

The sound insulation of a material has a strong dependence on the mass because the heavier material greater fraction of incident sound energy is reflected.

The materials have different characteristics in terms of energy dissipation through them, resulting generally best for soundproofing those which combine a high mass with a high energy dissipation capability.

The best results in terms of soundproofing materials are combined with consequent high surface mass with absorbent materials.

viernes, 14 de diciembre de 2012

Acoustic absorption coefficients (II)

For certain types of rooms used to be occupied by a large number of people in its design question arises how will its acoustic behavior in different conditions for optimal occupancy of the same design.

It is necessary to estimate the sound absorption provided by people and furniture from the corresponding sound absorption coefficients.
 
We complete the table acoustic absorption coefficients publishedwith the following table:


MaterialsCoefficients
125Hz250Hz500Hz1000Hz2000Hz4000Hz
Area of empty chairs with upholstered high percentage of surface0.720.790.830.840.830.79
Area of empty chairs with upholstered surface average percentage0.560.640.700.720.680.62
Area of empty chairs with upholstered surface low percentage0.350.450.570.610.590.55
Area occupied chairs with upholstered high percentage of surface0.760.830.880.910.910.89
Area occupied chairs with upholstered surface average percentage0.680.750.820.850.850.86
Area occupied chairs with upholstered surface low percentage0.560.680.790.830.830.86
Wooden seat0.010.020.030.040.060.08
Wooden seat occupied0.340.390.440.540.560.56
Seat upholstered with leather or vinyl0.100.150.250.250.250.25
Seat upholstered with plastic0.200.200.250.300.300.30
Seat upholstered with velvet0.300.320.270.300.330.33
Group of people standing0.250.440.590.560.620.50


miércoles, 12 de diciembre de 2012

How to soundproof a room

Neighborhood noises are one of the main reasons for dissatisfaction and discord in neighboring communities.
Different customs, schedules and lifestyles of people living together with insufficient acoustic performance of buildings cause most of the noise nuisance.

In this post I will raise a solution for soundproofing a room in order to avoid disturbing the neighbors.

The main objective should be to achieve maximum possible dissipation of sound energy transmitted to adjacent enclosures.

First indicate that the solution to such problems is to treat all surfaces of the room and not only shared with the site/s to which you want to avoid transmitting sound.

A possible proposal for soundproofing a room is as follows:

Acoustic treatment room ceiling

For the treatment room ceiling we propose the implementation of a ceiling with  gypsum plaster boards. This solution will decrease by at least 15 cm the room's height.
The construction details of the proposed solution is as follows:

1- Gypsum plasterboards.
2- Absorbent material (mineral wool 40 mm thick).
3- Metal fork
4- Multilayer panel.
5- Wrought

The steps for implementation are as follows:

Covering the surface of the original roof with panels that combine a multilayer composite foil which combine a viscoelastic sheet  with mineral wool at least 4 cm in thickness. These panels will be placed to the side of viscoelastic sheet seen. I leave two links of such commercial products:
Through this type of solution the sound reduction index of a unidirectional wrought based 30 cm beams can be improved by 15 dB , vaults and compression layer of reinforced concrete.

Then run the metal frame for fixing plasterboard plates following these steps:
    • Attach the threaded rods of the roof joists.
    • Place the metal brackets for attaching the metal profiles.
    • Place the metal sections that join the gypsum plasterboards.

Aliminium profiles structure

I leave some links of such commercial products:
Screw plasterboard plates to metal profiles seal the joint between plates.
Plasterboard plates bolted to metal profiles

Place mineral wool thickness of 40-50 mm on plaster boards and metal profiles.

Sound absorbing material

I leave some links of such commercial products:
Acoustical treatment of walls

When a room is to soundproof the walls of the enclosure require acoustic treatment to prevent the transmission of noise to adjacent enclosures.

A common mistake is to consider that only other premises adjoining enclosures require treatment.

Here we propose a cladding with the following elements:
  • Viscolelastic sheet.
  • Mineral wool.
  • Plasterboard plates bolted to aluminum profiles.
The following figure shows a construction detail:

Cladding detail

1. Viscoelastic sheet.
2. Mineral wool.
3. Plasterboard plates.

The implementation process is as follows:

First you must remove the baseboard and then set the sheet with adhesive on the surface of the treated wall.


These films improve insulation to airborne sound especially in the low frequency spectrum. Sheets are recommended with a minimum mass of 6 kg/m2.

The sheets are supplied in rolls, usually 1 m wide, which may present the adhesive already incorporated.

The installation mode is recommended from the bottom up, occupying the full height of the wall. The different sections should overlap each other by about 2 cm.

I leave two links of such commercial products:
This is followed by placing the metal profiles, which must be removed about 2 cm of the sheet, to enable the creation of a small air chamber. Profiles must be assembled with a modulation of 60 cm.



This is followed by the insertion of the acoustic absorption material between the uprights. It can be used mineral wool thickness of 40 mm and a density of 35-40 kg/m3. Its function is to dissipate the sound waves that are stationary in the air. To perform this function should allow air flow through its interior, so that the sound energy is converted into heat energy by the effect of friction. The use of higher density mineral wool does not provide better performance. Thereof may be employed absorbent materials suitable for the roof.


Finally we proceed to the junction of the plates by screwing plasterboard to metal profiles.


Floor acoustic treatment

Last but not least, you should proceed to the acoustic treatment of the room floor.

The aim is to prevent the transmission of noise to the walls of the room. This requires executing a floating floor avoiding any rigid connection with the walls.

We propose as a platform floating placed directly on battens:


1- Wrought.
2- Absorbent material 40 mm thick.
3- Polyethylene sheet.
4- Battens.
5- Prints laminated flooring.

This constructive solution can be run directly on the floor or on the existent slab. The only thing to keep in mind is that the area that serves as support does'nt present slopes greater than 1 cm.

The steps in implementation are the following::

First play must verify that the supporting surface is clean, free of defects and with a height of less than 1 cm.

Adhere to the two faces of each batten crosslinked polyethylene layer, uniformly distributed over the surface battens spaced about 60 cm and fix the cleat and lag wrought by each 90 cm.

I leave two links of such commercial products:
Fixing the battens to the slab

Then absorbing material is placed between the strips. Thereof may be employed absorbent materials suitable for the roof and walls.


Acoustic absorption material

Finally set the stage blades on battens, in the encounter with the walls should be placed polyethylene band which is placed on the baseboard.

Floorboards on battens

Constructive solutions described allow a substantial improvement in airborne sound insulation in walls of a room without a significant loss of usable space in the same.


martes, 11 de diciembre de 2012

Sound absorption coefficients for various materials


The following table shows the sound absorption coefficients as a function of frequency for various materials commonly employed in construction:


MaterialsCoefficients
125Hz250Hz500Hz1000Hz2000Hz4000Hz
Brick, unplastered0.030.030.030.040.050.07
Brick, without plastering, painting0.010.010.020.020.020.03
Lime and sand plaster0.040.050.060.080.040.06
Plasterboard0.290.100.050.040.070.09
Carpet on concrete0.020.060.140.370.600.65
Porous lightweight concrete block0.360.440.310.290.390.25
Painted concrete block0.100.050.060.070.090.08
Concrete or terrazzo flooring0.010.010.0150.020.020.02
Marble tiles0.010.010.010.010.020.02
Wood0.150.110.100.070.060.07
Plywood panel thickness of 1 cm0.280.220.170.090.100.11
Chipboard panel0.470.520.500.550.580.63
Hardwood0.040.040.070.060.060.07
Hardwood on concrete0.040.040.070.060.060.07
On hardwood slats0.200.150.120.100.100.07
Rubber carpet 0.5 cm thick0.040.040.080.120.030.10
Curtain 475 g/m20.070.310.490.750.700.60
Polyurethane foam 35 mm (Fonac)0.110.140.360.820.900.97
Polyurethane foam 50 mm (Fonac)0.150.250.500.940.920.99
Polyurethane foam 75 mm (Fonac)0.170.440.991.001.001.00
Polyurethane foam 35 mm (Sonex)0.060.200.450.710.950.89
Polyurethane foam50 mm (Sonex)0.070.320.720.880.971.00
Polyurethane foam 75 mm (Sonex)0.130.530.901.001.001.00
Glass wool 14 kg/m3 and thickness 25 mm0.150.250.400.500.650.70
Glass wool 14 kg/m3 and thickness 50 mm0.250.450.700.800.850.85
Glass wool of 35 kg/m3 and 25 mm thick0.200.400.800.901.001.00
Glass wool of 35 kg/m3 and 50 mm thick0.300.751.001.001.001.00
Ordinary window glass0.350.250.180.120.070.04
Brick wall plastered with gypsum0.0130.0150.020.030.040.05
Swimming pool surface0.0080.0080.0130.150.0200.25
Doors and windows opened1.001.001.001.001.001.00