Building acoustics

[edit] Introduction

Building acoustics is the science of controlling noise in buildings. This includes the minimisation of noise transmission from one space to another and the control of the characteristics of sound within spaces themselves.

Building acoustics are an important consideration in the design, operation and construction of most buildings, and can have a significant impact on health and wellbeing, communication and productivity. They can be particularly significant in spaces such as concert halls, recording studios, lecture theatres, and so on, where the quality of sound and its intelligibility are very important.

Building acoustics can be influenced by:

• The geometry and volume of a space.
• The sound absorption, transmission and reflection characteristics of surfaces enclosing the space and within the space.
• The sound absorption, transmission and reflection characteristics of materials separating spaces.
• The generation of sound inside or outside the space.
• Airborne sound transmission.
• Impact noise.

[edit] Characteristics of sound

Sound intensity is measured in Decibels (dB). This is a logarithmic scale in which an increase of 10 dB gives an apparent doubling of loudness.

Sound pitch is measured in Hertz (Hz), the standard unit for the measurement for frequency. The audible range of sound for humans is typically from 20 Hz to 20,000 Hz, although, through ageing and exposure to loud sounds the upper limit will generally decrease.

As well as intensity and frequency, sound also transmits information. For example, music or speech, transmit information which people may perceive differently from other sounds.

[edit] Reverberation time

The ‘reverberation time’ of a space changes the way the space ‘sounds’ and can affect the intelligibility acoustic information. A high reverberation time can make a room sound muffled, loud and noisy. Rooms designed for speech typically have a low reverberation time, whereas a higher reverberation time can add depth, richness and warmth to music.

The reverberation time of a room is defined as the time it takes for sound to decay by 60 dB after an abrupt termination. It is linked to the total quantity of soft treatments and the volume of the room.

See Reverberation time for more information.

[edit] Sound absorption

Sound absorption is the loss of sound energy when sound waves come into contact with an absorbent material such as ceilings, walls, floors and other objects, as a result of which, the sound is not reflected back into the space. Acoustic absorption can be used to reduce reverberation times.

Absorbent materials are sometimes categorised from A to E, where A is highly absorbent and E is almost fully reflective.

Sound absorbers can be divided into three main categories:

• Porous absorbents, such as fibrous materials or open-celled foam.
• Resonance absorbents, which consist of a mechanical or acoustic oscillation system, such as membrane absorbers.
• Single absorbers such as tables, chairs or other objects.

See sound absorption for more information

[edit] Sound insulation

Sound transmission paths can be interrupted by sound insulation and by blocking air paths. The sound insulation of a single leaf of a material is governed by its mass, stiffening and damping.

The sound insulation across a good conventional, lightweight, office to office construction is typically in the order of 45 dB Dw. This means that if the sound level in the source room is around 65 dB (a typical level for speech), the sound level in the adjacent room, the receiver room, will be approximately 20 dB (barely audible).

If sound levels are increased in the source room however, to 75 dB (raised voice), sound levels within the adjacent room will also increase to around 30 dB (audible). Sound insulation therefore describes the level of sound lost across a partition and not the level of sound within an adjacent room.

Dw represents the sound insulation between rooms on-site. Rw represents the lab tested sound insulation of an element making up a partition wall/floor type. Standards achieved in labs may not be possible on site because of the quality of workmanship and due to sound ‘flanking’ acoustic elements, that is, travelling around them through an easier path, rather than only directly through them as under lab conditions.

The building regulations part E sets minimum standards for design and construction in relation to the resistance to the passage of sound.

See Sound insulation for more information.

[edit] Noise nuisance

Building acoustics can help to mitigate the effects of noise disturbance which can have negative effects on health, wellbeing and general quality of life.

The Noise Policy Statement for England (NPSE) defines noise pollution as:

• Environmental noise – which includes noise from transportation sources.
• Neighbour noise – which includes noise from inside and outside buildings.
• Neighbourhood noise – which includes noise arising from industrial and entertainment premises, trade and businesses, construction sites and noise in the street.

This can be an important consideration for the location, design and construction of new developments.

See Noise nuisance for more information.

[edit] Related articles on Designing Buildings Wiki

• Acoustic consultant.
• Airborne sound.
• Approved Document E.
• Ash deafening.
• Audio frequency.
• BREEAM Acoustic performance.
• Building Bulletin 93: acoustic design of schools.
• Building regulations.
• Decibel.
• Flanking sound.
• Impact sound.
• Noise nuisance.
• Pre-completion sound testing.
• Reverberation.
• Robust details certification scheme.
• Sound absorption.
• Sound insulation.
• Sound insulation in dwellings: Part 1: An introduction (GG 83-1).
• Sound reduction index (SRI).
• Sound v noise.
• Structure-borne sound.