| SOUND 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, kindergartens etc as the voices of children ar particularly dominant in this frequency area. The below figure shows how the decibel and frequency range relate to common everyday sounds and the threshold of hearing curve. Sounds below this curve are not heard by the human ear.  Fig. A. The human ear responds to decibel changes in broadly the following way: • A 1 dB increase is the smallest audible change in level. It would only be noticed if the two sounds were presented in quick succession. • A 3 dB increase is the smallest audible change which could be detected over a period of time. • A 10 dB increase represents a doubling of loudness to the ear. |
