AcousticsAcoustics

A Group 1 presentation

Presentation Outline

a) Define the following:

i. Room acoustics

ii. Sound absorption

iii. Sound reflection

b) Discuss different construction materials that can be used to improve

acoustical properties of a concert hall.

Room AcousticsRoom Acoustics

What is room acoustics?

• Also known as architectural acoustics, room acoustics is a science and engineering of achieving good sound within a building.

• It is concerned with the control of sound - how it is created, propagated, perceived, measured and modelled - in an enclosed space with the aim of providing the best condition for the production and reception of desirable sounds.

• Enclosed spaces can be dwellings, offices, workshops, factory halls, lecture rooms, auditoria, concert halls, transportation terminals, etc.

What is room acoustics?

• The sound within a room is mainly from two things which are

1. Reflection from various objects within a building and also

2. Sound from a particular source e.g. human voice or speakers.

Room

Acoustics

Fig 117

Structure-borne

sound transmission

Room

Acoustics• Sound incident on a solid

body is partly reflected,

partly absorbed (i.e.

converted into heat) and

partly transmitted into air

on the opposite side.

Room

Acoustics

Fig 119

Direct and

reverberant sound

Room Acoustics

• Acoustic requirements for different rooms depend on nature and purpose of the space and these

include:-

1. An adequate level of sound evenly distributed to all listeners in the room

2. Background noise and external noise reduction to acceptable levels

3. A rate of decay (reverberation time) suitable for the type of room

4. Absence of echoes

Room Acoustics

• Therefore, there are 3 ways to improve room acoustics:

A. Absorb (via drapes, carpets, ceiling tiles, etc)

B. Block (via panels, walls, floors, ceilings and layout)

C. Cover-up (via sound masking)

Sound AbsorptionSound Absorption

What is sound absorption?

• Sound, or acoustic absorption refers to a material, structure or object

absorbing sound energy when sound waves collide with it, as opposed to

reflecting the energy. Part of the absorbed energy is transformed into heat

and part is transmitted. The energy transformed into heat is said to have

been 'lost'.

What is sound absorption?

• Sound absorption (denoted by A) is the product of the absorption

coefficient (a) and the area of a given surface (s):

𝐴 = 𝑎 × 𝑠

• Absorption coefficient is used to indicate all the sound that is not reflected

by a surface (i.e. it includes the part actually absorbed and that which is

transmitted).

Sound

Absorption

r = reflected

a = absorbed

t = transmitted

r + a + t = 1

Sound ReflectionSound Reflection

What is sound reflection?

• Reflection is the change in direction of a wavefront at an interface between

two different media so that the wavefront returns into the medium from

which it originated.

• The reflection of sound follows the law of reflection, which says "angle of

incidence equals angle of reflection". The same behavior is observed with

light and other waves, similarly depicted by the bounce of a billiard ball off

the bank of a table.

Sound ReflectionFor a smooth surface the angle of incidence (θ1) equals the angle of reflection (θ2), as

measured with reference to the normal (line perpendicular) to the surface.

What is sound reflection?

• When sound is in an enclosed space, reflection will occur from the bounding

surfaces; the reflected part will reinforce the sound within the space and the

remainder will be lost for the system.

• It is essential to note that within an enclosed space there is a complex pattern

of interreflected sound, known as reverberant sound.

Acoustic MaterialsAcoustic Materials

The Concert Hall

• The boundaries of concert halls are used to control the acoustic. For instance, the walls can be made hard to reflect sound back into the room, soft to absorb sound or rough to disperse sound in different directions.

• The various materials that can be used to improve acoustical properties of a concert hall fall under these 3 major categories:-

1. Reflectors

2. Absorbers

3. Diffusers

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Bibliography

• What is Room Acoustics? www.bksv.com

• O. H. Koenigsberger, et al (1974), Manual of tropical housing and building, Part

one: Climatic design, Longman

• Acoustic reflection, www.acoustics.salford.ac.uk

• Concert Hall Acoustics: Art and Science, www.acoustics.salford.ac.uk

• Marshal Long (2006), Architectural Acoustics, Elsevier

The EndBlessing Mukome, Jnyr Mutaringe, Coster Bangwayo, Ngoni

Mudziki, Tatenda Chikadaya

©2014. A Building Services II Presentation