ABSTRACT
By sound radiation power is transmitted to the surrounding space but sound radiation is not necessary to generate audible sound. Depending on the movement characteristics of the loudspeaker driver’s diaphragm (the local amplitude and phase of vibration over its surface), the wavelength of sound in air, and the acoustic environment, there may be either:
• sound power radiated to the far eld (acoustic energy is transmitted away from the diaphragm) or
• a local reactive near-eld sound pressure, that is, the diaphragm is moving the air in its vicinity but without power radiation to the far eld (close to a plate carrying bending waves below the critical frequency)
From the viewpoint of audio, however, the latter can of course be considered as sound generation as well since there is sound pressure in the near-eld and this is what we hear.
