Читать книгу Engineering Acoustics - Malcolm J. Crocker - Страница 110

The sound intensity radiated by a dipole is seen to depend on cos² θ (see Figure 3.11). Most real sources of sound become directional at high frequency, although some are almost omnidirectional at low frequency. This phenomenon depends on the source dimension, d, which must be small in size compared with a wavelength λ, so d/λ ≪ 1 for them to behave almost omnidirectionally.

Figure 3.11 Polar directivity plots for the radial sound intensity in the far field of (a) monopole, (b) dipole, and (c) (lateral) quadrupole.