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Learn Sound Control

Why controlling sound is so important

Acoustic absorption is essential in creating a controlled listening environment, whatever the application may be. Without treatment, a space can have long, unpleasant reverb times which will inevitably mask the original sound source. Read More

Excess noise or reverb is caused by sound bouncing off hard surfaces within a space. The sound is then exacerbated in certain frequencies creating distortion and what is known as peaks and troughs. This effect can break up a sound, make it difficult to hear conversation and create an overall irritable experience. Acoustic panels placed within the space will absorb this excess noise and give the sound source more clarity.

High performing insulation such as glass and rock-wool are great low cost materials that provide effective acoustic absorption. Designed specifically for inside the walls of factories and other high SPL (sound pressure level) environments, when the material is placed on the outside of the wall, it can create a quieter listening environment within that space.

How sound absorption actually works

For sound to be effectively absorbed using a minimal amount of space and depth, it has to pass through a porous material that contains a high number of air pockets in its structure. Each time it hits matter and then air, it causes friction and the sound energy is converted into heat energy (extremely low amounts) - this is known as disapacion. Read More

This makes fibrous or foam like structures highly efficient at the sound absorption process. Typical products are those made from fibreglass, mineral rock wool, polyester and other synthetic materials which usually make up foam.

The thickness and density of the absorption material will also determine the bandwidth of the frequencies being absorbed. The thicker the absorber, the lower the bandwidths cut off frequency that is being absorbed. But density (or gas flow resistivity, read below) must also be in correspondence to this, otherwise it starts becoming reflective. The general rule is; thicker = less dense, thinner = more dense.

Other commonly used techniques are also used when absorbing sound also. Having an air gap equivalent in depth behind the absorption material will increase the efficiency and low end absorption. This is true because porous absorbers are most effective when particle velocity is at its highest, i.e when the air particles being moved by the sound wave are traveling its fastest. When a sound wave encounters a hard fixed surface (i.e. a wall), this point of maximum particle velocity occurs at a distance that is ¼ of the sound waves wavelength (see diagram below).

The air gap/material depth rule applies because of the varying wavelengths across the frequency spectrum. As the air gap exceeds the depth of the absorption material, the law of diminishing returns is applied. Resonating materials such as MLV are also used for sub bass frequencies where the sound waves are far too long for any practical broadband absorber.

Diffusion and absorption

Diffusion and absorption are technically the opposites of each other but are often used hand in hand. Timber or other hard surfaces that are generally designed with mathematical equations are used to create pleasant sounding reflections when absorption removes the sound all together. Read More

Diffusion has the intention of keeping sound energy in a space by having it randomly diffused, when absorption removing the sound creates a much quieter environment. Diffusion is often used in recording spaces to give depth and tonality to recordings when the particular room sound is desirable. Absorption is more preferred in mixing or critical listening spaces where less room noise is wanted and speaker noise is prioritised. Even though there are methods and common procedures for the approach of these types of rooms with the use of absorption and diffusion, the decision will often come down to personal preference.

Treatment Vs Proofing

Sound treatment and proofing are commonly misinterpreted as the same thing, but they are two distinctly different procedures. Treatment refers to creating a more controlled listening environment and will minimise the sound within a given space. Sound proofing on the other hand is a whole different ball game and more specifically refers to the elimination of sound transfer between spaces. Read More

Proofing can be quite complex and depends on each particular situation. Porous absorbers such as acoustic panels, are poor sound insulators. This means sound will travel quite easily through them and will not be very effective at stopping sound from travelling from one room to the next. What they can do is lower the level of reverberation in a room, therefore lowering the overall sound that could be transferred.

Our panels are designed to absorb sound and will do just that, but they are not specifically designed to stop noise transfer. Proper proofing should be considered before the time of construction of a building and is generally difficult to achieve after the fact. Unfortunately there is often no cheap alternative and proofing is not a service we provide. Commonly used sound proofing materials include MLV (mass loading vinyl), bricks, concrete and other highly dense substances.

Densities and gas flow resistivity

There is often some confusion in the audio community relating to densities and different absorption materials. The most common misunderstanding is that density is mostly relevant as it is titled on most insulation products, when in fact a more translatable unit of measurement is 'gas flow resistivity’. Read More

Two materials for example, glass wool and rock wool, with the same densities will have slightly different absorption performances as the core material is different. Gas flow resistivity is measured in rayl/m2 or Pa.s/m2 and is the resistance provided by the material that impedes the flow of sound energy. There are a number of forums on Gearspace.com about this topic.

When sound energy transfers from one medium (air) to another (insulation material), there is usually an impedance difference at the interface where they meet. What this means is that when the sound wave reaches the surface of the material, if the material is too dense or too torturous a sound path due to the complexity of the fibres with the core structure; then the impedance that the sound wave encounters is too high, and most of the sound energy cannot penetrate and is reflected. If the impedance encountered is too low, then the sound wave will travel through the material without losing much energy (i.e. not absorbed).

There is an optimum balance where the impedance encountered is low enough to allow the sound energy to enter the material easily, but high enough to absorb it. Unfortunately this is not a single number, as it is entirely dependent on frequency.

10,000Hz = oscillating air particle 10,000 x per second
100Hz = oscillating air particles 100 x per second

High frequency sound waves lose energy much quicker than low frequencies as they are moving much faster at each time losing energy as they interact with the material. So for example, a low density porous material will absorb more high frequencies than low frequencies. If you increase the density, it will start absorbing more low frequencies also. If you keep increasing the density, sound energy will begin to be reflected and this will usually start occurring at the higher end of the frequency spectrum.

Absorption coefficients, Noise Reduction Coefficients (NRC) and R-values

Absorption coefficients are often found on charts for displaying the performance of sound performance on a given insulation. Read More

Each coefficient represents the fraction of sound energy that is either being absorbed or transmitted; i.e. the fraction of sound energy that is not reflected and is usually given in 1/1 octave band frequencies (i.e. 250Hz, 500Hz, 1000Hz etc.)

Noise Reduction Coefficient (NRC) is the average of absorption coefficients over 250-2000Hz and is a commonly used single number rating. It is used to more easily determine the products over all performance.

R-values are often misinterpreted as being related to sound, but is a thermal performance rating and not associated with acoustics (they are designed to go in walls after all).

Polyester vs other insulation absorbers

We use Polyester insulation in all of our products for a number of reasons. One standout factor that Polyester has over other insulation materials is that it's 100% allergy free. The batts contain no breathable fibers and poses no potential health risks, whereas others do. Read More

Polyester is also extrememly durable and will last a lifetime. The material is made from recycled plastic bottles minimising its environmental impact and is relatively lightweight. Polyester insulation is one of the most recent inventions in the building industy and can be used for a number of applications. Modern acoustic treatment products are almost all made from Polyester due to its flexibility and ability to be coloured, shaped and moulded to any size without the need of covering.

The mis-marketed achrosity, ‘foam’

Often when people treat a room, they do so with low density, inexpensive foam. Why? Because it’s cheap to make and lightweight, it is easily sent around the world from large manufacturers. Read More

Foam has unfortunately flooded the market for quite some time and should really not be considered an effective absorber. Companies often market them as ‘studio grade foam’ or ‘sound proofing foam’ which is falsely advertised. These products target only the high end of the frequency spectrum, unaffecting the mid and lows which is necessary for critical listening spaces. Therefore, thicker and denser materials such as insulation are far more suited.