ABSTRACT
This chapter introduces the relation between sound power and sound pressure and discusses radiation field, near field and far field of a sound source. It examines sound power determination using sound intensity measurements, surface vibration measurements and sound pressure measurements, both in the laboratory and in the field. The chapter explores some uses of sound power information. Sound pressure is the quantity most directly related to the response of people and things to airborne sound and this is the quantity that is most often to be controlled. When the sound power level of a source is specified, unless otherwise stated, the assumption is implicit that the radiation impedance presented to the source is the same as it would be in a free unbounded space, commonly referred to as “free field”. The determination of the sound power radiated by a machine in the free field, using pressure measurements alone, requires that any reverberant sound be negligible.
