Acoustics: Sound Fields, Transducers and Vibration, 2nd Edition

7.2. Unbaffled direct-radiator loudspeaker

A baffle is a structure for shielding the front-side radiation of a loudspeaker diaphragm from the rear-side radiation which can potentially cancel it at low frequencies. The necessity for shielding the front side from the rear side can be understood if we consider that an unbaffled loudspeaker at low frequencies is the equivalent of a pair of simple spherical sources of equal strength located near each other and pulsing out of phase (see Fig. 7.2). The rear side of the diaphragm of the loudspeaker is equivalent to one of these sources, and the front side is equivalent to the other.

If we measure, as a function of frequency f, the magnitude of the rms sound pressure p at a point A, fairly well removed ...