Glossary

This page provides brief descriptions and definitions of some key acoustical terms.

frequency (f) = the number of cycles per second of a vibrating object or medium

Hertz (Hz) = the unit of frequency equal to 1 cycle per second

1 kHz = 1000 Hz

sound pressure level (SPL) = 200 log10 (Prms / P0) dB where Prms is the sound pressure level at the measurement position and P0 is the reference pressure, 0.00002 Pa

sound power level (SWL) = 10 log10 (W / W0) dB where W is the sound power of the source and W0 is the reference acoustic power, 10^-12 watt

dB(A) - the sound pressure level as measured with a sound pressure level meter using an A-weighting network which differentiates between sounds of differing frequencies in a similar way to the human hearing system

dB LAeq,t - the equivalent continuous A-weighted sound pressure level having the same energy as a fluctuating sound over a specified time period t

dB LA10,t - the A-weighted sound pressure level which is exceeded for 10% of a specified time

period T - this parameter is frequently used for road traffic noise monitoring and prediction, although LA10 figures are often converted to LAeq figures for assessment purposes

dB LA90,t - the A-weighted sound pressure level which is exceeded for 90% of a specified time

period t - this parameter is often taken to represent the background noise level

dB LAmax - the maximum A-weighted sound pressure level recorded during a noise event or noise

Monitoring period - the sound level meter time-weighting (fast or slow) is normally stated

Vibration Dose Value (VDV) as defined in BS6472 is calculated by taking the fourth root of the integral of the fourth power of acceleration after it has been frequency-weighted - the frequency- weighted acceleration is measured in m/s 2 and the time period over which the VDV is measured is in seconds, which yields VDVs in m/s^1.75