Sound Definitions

Sound Absorption

The sound absorption property of a material expresses the ratio of incident sound and absorbed sound. The sound absorption material can vary, depending on how it is installed and the depth of any air space behind it.

Room Acoustics

This is the behaviour of sound within a room, which is linked to the room size and shape together with the performance of the internal surfaces and the construction type. The mixture of “hard” surfaces that reflect sound and “soft” surfaces that absorb sound will create the room acoustics.

Reverberation Time

Reverberation time is defined as the time it takes for the sound pressure level to drop by 60 dB. A short reverberation time gives the best possibilities for a clear and distinct sound picture, good speech intelligibility and minimising annoying background noise.

Long reverberation times, which are typical in rooms with many hard surfaces, lead to poor speech intelligibility and echoes and often contribute to an unpleasant indoor environment.

Speech Intelligibility

This can be defined as how clear speech communication is, and it is directly related to the reverberation time and the background noise level in a room. The speech intelligibility of a room can be measured through innovative software and is particularly important in lecture halls and theatres, where voices need to “carry” without losing the crispness of the sound.

Sound Insulation

Sound insulation is about preventing sound from spreading to surrounding areas. Sound insulation can be measured from “room to room” or from “plenum to room” and is recorded in dB.

Sound is a form of energy, which is transmitted through the air and perceived by the human ear. Sound is described by its “sound pressure level”, which is measured in decibels (dB) and its frequency, which is measured in Hertz (Hz).

The human ear can typically hear sounds in the decibel range 0-120 dB and can detect sounds in the frequency range 20-20,000 Hz, but it is not equally sensitive across these ranges.

The human ear is most sensitive at around 4000 Hz and so high sound absorption is required around 4000 Hz. This is particularly important in schools, kindergardens etc as the voices of children are particularly dominant in this frequency area.

Whatever the sound, it can be perceived in a pleasant or unpleasant way and this is greatly influenced by the acoustics of the space.