Sound paths in rooms

· A sound path or sound ray is the direction of the wave vibrations as they travel through a material such as air.

· The behaviour of sound paths inside an enclosed space can be affected by the:

1. Reflection
2. Absorption
3. Diffraction
4. Transmission

A. Sound Reflection

· Reflected sound is produced by the direct sound bouncing off the walls, floor etc.

· The sound loses some energy at each reflection, depending on the nature of the surface.

· Interiors that contains a lot of hard surfaces such as glass, stone, metal are said to be "live" because their high reflectivity.

· Soft or porous materials like carpeting, draperies and upholstered furniture, are sound deadening.

· There are two types of reflection from room surfaces:

a. Concave surfaces tend to focus sound.

b. Convex surfaces tend to disperse sound.

B. Sound Absorption

· Sound absorption is a reduction in the sound energy reflected from a surface.

· Sound absorption is a major factor in producing good room acoustics when controlling reverberation.

· The absorption coefficient is a measure of the amount of sound absorption provided by a particular type of surface.

· The amount of sound energy not reflected is compared with the amount of sound energy arriving at the surface.

Absorption coefficient (a) = Absorbed sound energy

Incident sound energy

Unit: none – its value expressed in a ratio.

For example, a surface that absorbs 40% of incident sound energy has absorption of 0.4.

· The absorption coefficients of a surface depends on:

1. Type of building materials
2. Frequency of the incident sound

· The effective absorption of a particular surface depends on:

1. The absorption coefficient of the surface material
2. The area of that particular surface exposed to the sound.

Absorption of surface = Area of surface x Absorption coefficient of that surface

Unit: m² sabin

C. Sound Diffraction

· The acoustical phenomenon which causes sound waves to be bent or scattered around obstacles such as corners, columns, walls, beams is called sound diffraction.

· In general, diffraction means sound is interrupted by an obstruction and a sound wave can spread out beyond small openings.

· Diffraction also happens at convexly curved terrain surfaces, e.g. at the edges of slopes and hills. Diffraction formed by upward refraction sound waves contributes sound energy into shadow zones. Therefore, it is not completely quiet in shadow zones.

Diffraction into an acoustical shadow behind a hill

The Figure below shows the noise barrier constructed on side of roads to avoid traffic noise from disturbing tenants and dwellers in buildings and houses nearby. Although building a noise barrier, the noise is not totally omitted. This kind of phenomenon with sound coming around from behind is called “Sound diffraction”. The barrier can effective minimize noise that has high frequency with short wavelength but not low frequency sound. This is because low frequency has long sound wavelength that can bend into the sound shade area.

D. Sound Transmission

Noise is transferred into buildings and between parts of building by two main mechanism:

Дата добавления: 2015-11-14