Acoustic Panels 

An acoustic panel is material that controls the sound or noise level in a room. These panels reduce or absorb the sounds that echo, reflect or reverberate in a room or studio, thus improving the sound quality for listening or recording.  Acoustic panels are available in different types, such as wall panels, ceiling panels and door panels.

Acoustic treatment

Sound emanates from your speakers and strikes your ears, but also continues past your ears and bounces off the surfaces of your walls, floor and ceiling. This reflected sound distorts and exaggerates the sounds cape. This can make a room sound boomy or muddy and difficult to clearly hear the dialogue in a movie or vocals in a musical performance.

Acoustic treatment is a systematic approach to improve the audibility in a room. It involves improving the quality of desired sound and reducing the unnecessary sound waves by using acoustic panels, baffles and absorbers.

Acoustic insulation

Sound travels in waves and flows much like water or air. Any hole or opening that could let a draft in will let noise in.

Acoustic insulation prevents sound from traveling from one room to another by using materials that resist transmission of sound waves. Acoustic panels are very useful for the purpose of acoustic insulation in residential and commercial applications.
There are normally three approaches to controlling or eliminating noise:

1.   Contain the noise at the source
2.   Identify, isolate, and treat the paths noise will take
3.   Reduce noise entering specific spaces

Acoustic foam

Acoustic foam (also known as studio foam) is an acoustic insulation material which provides strong sound absorption and noise reduction over a wide range of frequencies with its eggcrate structure and is easy to install. This foam absorbs undesired sound and thus, improves quality of desired sound.

Decibel (dB)

A decibel is the unit for the measurement of sound energy. One decibel is the minimum change in the volume that can be perceived by a human ear. In the field of acoustics, sound intensity is expressed in decibels.

It is a dimensionless unit which denotes the ratio between two quantities that are proportional to power, energy or intensity. One of these quantities is a designated reference by which all other quantities of identical units are divided. The sound pressure level in decibels is equal to 10 times the logarithm (to the base 10) of the ratio between the pressure squared divided by the reference pressure squared. The reference pressure used in acoustics is 20 micro Pascals.

Absorption coefficient

Absorption of a surface is characterised by the Absorbtion Coefficient, defined as the proportion of the sound (intensity) absorbed by the surface. It is frequency dependant and has a value of 1 for a perfect absorber and 0 for a perfect reflector.

Comparing the absorption of materials should involve a comparison of their respective absorption coefficients in the different bands. Provided the materials are tested in a similar fashion, the material with a higher absorption coefficient in a particular band will absorb more sound in that band when you use it in your room. Be careful though: Materials are tested using different mounting methods. For example, if one material is tested by laying the materials out on a predetermined area of the floor – called A mounting – and another tests their materials by spacing them off the floor by several inches, then the comparisons are “apples and oranges.” To truly compare, find numbers derived from tests that used the same layout of materials in the test chamber. Also, there are three main standard methods used to test materials for absorption. Two of them are reverberation chamber methods – ASTM C423 in the U.S.A. and ISO 354 in Europe. These two methods are quite similar, but the ISO method – in general – will produce slightly lower overall numbers than the ASTM method. The other method is the impedance tube method, or ASTM C384. This method places a small sample of the material under test at the end of a tube and measures the absorption. Again, the numbers from this test are usually lower since a different method of calculation is used. They are also not as representative of real-world applications of materials relative to the reverberation chamber methods.

Absorbers

An absorber’s function is to absorb the unnecessary sound that is reverberated or echoed. Absorber products are made of different materials as per application requirements.

Physical Properties: Porous fibrous and sometimes covered with protective membranes. Noise enters the absorber and is partly dissipated (abosrbed) within the material. Some is transmitted. Some is reflected. Absorber performance is expressed as a decimal value. A perfect absorber is rated at 1.00. The higher the decimal value the more effective the absorber will be.

Effectiveness is expressed as NRC (Noise Reduction Coefficient).

NRC: Percentage of acoustical energy absorbed calculated as an average of laboratory test data at several frequencies.

Brick, unglazed
.05
Concrete block
.05
1/8″ pile carpet
.15
5/16″ pile carpet and foam
.35
Concrete floor
.00
Plaster, smooth finish
.05
Plywood paneling, 1/4″ thick
.10
Water surface (as in swimming pool)
.00
1″ thick fiberglass curtain
.70
3″ thick “SONEX” wedge foam
.86
4″ thick smooth surface foam
.89
4″ thick metal panel
.95

Diffusers

A diffuser is a device that diffuses the echo or unnecessary sound reflected from walls or ceilings of a room. These devices work through scattering or random reflection of a sound wave from a surface. The directions of reflected sound is changed so that listeners may have sensation of sound coming from all directions at equal levels and this way the sound quality improves and the radiated energy is less direct or coherent.

For example, a flat concrete wall produces a pretty distinct echo when sound reflects off of it. However a brick wall, while still pretty reflective, tends to diffuse the sound reflections and produces a much less distinct echo. This is due to both the surface of the brick itself and the mortar between the bricks (more specifically the edge diffraction of the joint between the two). All surfaces will of course differ and it is usually a variety of surfaces that create the most randomized diffusion of sound. Diffusion is a very important consideration in acoustics because it minimizes coherent reflections that cause problems. It also tends to make an enclosed space sound larger than it is. Diffusion is an excellent alternative or complement to absorption in acoustic treatment because it doesn’t really remove much energy, which means it can be used to effectively reduce reflections while still leaving an ambient or live sounding space.

Sources:

http://www.business.com/guides/acoustic-panels-key-terms-37810/

http://www.sweetwater.com/expert-center/glossary/t–Diffusion

http://www.acousticalsolutions.com/glossary-of-terms

http://www.acoustics101.com/definitions.asp