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Sound absorption is the process by which sound waves are reduced in intensity as they encounter an absorptive material.

When sound passes through a material, some of the energy waves are converted into heat or other forms of trace energy, causing the sound to become quieter or less noticeable.

In certain settings, sound can prove to be troublesome since it can travel easily.

In larger buildings with high ceilings for example, echoes and reverberations are commonplace.

In controlled environments such as recording studios, sound needs to be controlled and calibrated to create an acoustically viable setting, optimise acoustic performance and maximise the recorded sound quality.

In both instances, sound absorption can help to improve the overall impact of sound and how it travels.

In the following chapters, we outline how sound absorption occurs, how absorptive materials are used to improve sound and how to apply them.

What is Sound Absorption?

Sound absorption is the term used to describe ways with which sound reverberation and echoes in a space are reduced via absorption, in order to enable a cleaner sound quality.

By means of sound absorption, there will be a noticeable loss of sound energy due to the soundwaves being absorbed by the material in question.

These materials can be porous or non-porous, and may include things like foam, open cell mineral, fiberglass, fabrics, cushions, throws, curtains or carpets.

Sound Absorption vs Soundproofing

Sound absorption and soundproofing are often thought to be one and the same, but this is far from being the case.

There are actually very distinct differences between these two terminologies.

As noted above, sound absorption refers to reducing echoes and reverberations.

By doing so, the overall volume of noise is reduced, and consequently clarity is increased.

As a general rule, sound waves bounce off solid surfaces.

While the direction of the sound may change, the echo will sound the same as the original sound but with an amplified effect.

As a result, the louder the source is, the more energy the soundwaves will have.

The longer the reverberation time is, the louder and more noisy a room will become.

That is why in some settings, sound absorption is very important, as the acoustic value in the space can become uncontrollable and unusable if it isn’t dealt with.

Some common examples where sound absorption is important include school classrooms, sports halls, concert venues, cinemas, theatres and recording studios.

Generally sound absorption is applied where possible or feasible – floors and walls, as well as ceilings and partition surfaces.

Soundproofing on the other hand refers to isolating and blocking noise from being transferred through the structures.

The sound energy is stopped from making its way to another room for instance.

With soundproofing, the main aim is to prevent as much sound energy as possible from being transferred by whatever means to the outside of the subject space.

This may be in way of varying principles of decoupling of the structure, absorption, deflection and thermal conversion.

Thermal conversion (Acoustiblok 3mm Isolation Membrane) is where the energy is converted into trace heat energy via vibration, or else, transmitted away from the location.

What Happens When Sound is Absorbed?

When sound is absorbed, the sound energy is transformed into heat energy.

This conversion is partly transmitted through the absorptive material.

If the sound is not absorbed it would be reflected or transmitted, thereby causing reverberations and echoing.

Generally, soft and pliable materials are good acoustic insulators as they manage to absorb more sound than hard and impenetrable materials.

The ability of a material to absorb sound is measured by its sound absorption coefficient or noise reduction coefficient, which ranges from 0 (perfectly reflective) to 1 (perfectly absorbing).

The coefficient is a function of the frequency of the sound wave, the angle of incidence, and the thickness and density of the material.

Material Sound Absorption Coefficients

Materials	Absorption Coefficients by Frequency (Hz)
Acoustic Ceiling Tile	.80	.90	.90	.95	.90
Brick	.03	.03	.03	.04	.05
Carpet on Concrete	.08	.25	.60	.70	.72
Heavy Curtains	.15	.35	.55	.75	.70
Marble	.01	.01	.01	.01	.02
Painted Concrete	.10	.05	.06	.07	.09
Plaster on Concrete	.10	.10	.08	.05	.05
Plywood on Studs	.30	.20	.15	.10	.09
Smooth Concrete	.01	.01	.01	.02	.02
Wooden Floor	.15	.11	.10	.07	.06

Type of Sound Absorbers

Sound absorbers can be divided in three categories, namely;

Porous Absorbents

Porous absorbents can be subdivided in two types, which are:

a) Fibrous

Such materials absorb soundwaves because as soon as they make contact with the material, the fibres will bend and generate heat energy.

Since the acoustic energy is converted to heat energy, the sound will be absorbed effectively.

b) Open-cell

In this case, air movement is generated as the soundwaves push through air particles.

This results in a viscous loss and heat is generated too.

Resonance Absorbents

Resonance absorbents, such as membrane absorbers, are composed of an acoustic or mechanical oscillation system.

This consists of a solid plate behind which there is an airtight space.

The sound absorption will reach its maximum at the resonance frequency.

The cavity might also be filled with a porous material in order to further broaden the absorption over the various frequency ranges.

Single Absorbents

Single absorbers can be any objects in the room or space, such as tables, chairs and bookcases.

Hence the sound absorbing characteristics of such materials will vary significantly.

Low frequency sounds which are lower than 500 Hz will be more difficult to absorb.

Conversely, high frequency sounds in excess of 500 Hz can generally be absorbed more easily by single absorbers.

Acoustic ceiling panels and acoustic wall panels are also classified under this category of sound absorbers.

Acoustiblok AcoustiClouds and Acoustiblok Absorber Panels can be used as ceiling panels or wall panels.

These panels are very effective when it comes to absorbing sound as they have a Class A sound absorption level (40mm & 50mm options) or Class C sound absorption level (25mm).

As a result, these panels increase acoustic absorption, thereby reducing the unwanted regeneration, reverberation, and resonance of the soundwaves.

They are also designed to enhance the appearance of the room since they are available in a vast assortment of colours and sizes.

Moreover, they are exceptionally easy to install.

They’re available with varying methods of installation – wall mounts systems, ceiling hooks, cable systems or with a self adhesive backing, which makes mounting them to walls and ceilings quick and effortless.

Simple and effective with easy installation to the intended surface.

Absorber panels come in standard or bespoke sizes, and have a fibrous core thickness of 25mm or 40mm (Class 0 fire rating).

Self adhesive panels are a non fibrous core of 50mm (fire resistant).

AcoustiWall panels and AcoustiCloud Ceiling Absorber Panels are designed with a fabric finish which is available in an extensive range of colours.

Fabric facing complies with Class 1.

Class 0 fabrics are also available on request.

How Do Sound Absorbing Acoustics Panels Work?

Sound absorption acoustic panels are one of the top options for effective sound absorption.

Such panels are made from a soft material which is specifically designed to absorb sound energy.

The panels will stop the sound energy from bouncing around the room, and will not reflect off the walls, ceiling and other surfaces.

As a result, the highest acoustic performance can be achieved, allowing for a better environment in terms of acoustic comfort and improving speech intelligibility.

That is why such acoustic panels are used in schools, hospitals, offices, restaurants and other commercial spaces, as well as in domestic settings.

Where are Sound Absorption Principles Used?

Sound absorption principles are used in various applications and settings.

Some examples include:

• Sound recording
• Sound reproduction
• Room and architectural acoustics
• Loudspeaker design
• Noise barrier walls
• Sonar
• Social spaces such as halls, schools, restaurants and bars
• Office space

What is an Anechoic Chamber?

An anechoic chamber is a room which is designed to absorb as much sound as possible.

In such a room the walls are made from a number of baffles that have highly absorptive materials.

The arrangement ensures that even if a fraction of the sound is reflected, it will be in the direction of another baffle rather than in the room.

As a result, such a chamber is essentially devoid of any echoing.

Setting up such a room is rather expensive and they are only created when there is the need to carry out experiments or to measure sound pressure levels, for example.

Large absorptive foam wedges are used on walls, ceilings and floors, and it is crucial for them to be big in order to be effective even for low frequencies.

The doors must be sealed well and ventilation, if any, needs to be very carefully set up to ensure that there are no leakages anywhere.

Conclusion

Spaces where noise can be amplified, reverberated or echoes need to be dealt with to reduce such problems.

It is important to consider the space as well as its particular purpose in order to choose a sound absorption solution that can be as effective as possible.

If you have a space in a commercial or residential setting that requires better sound control, contact us to arrange an expert acoustic consultation.

One of our acoustical experts will be able to help you to decide on the best way to improve overall sound quality and noise control within your space.