Computed directivity $D(\theta ,\frac{\pi }{4})$ in the $\phi =\frac{\pi }{4}$ plane for each octave band between 125 Hz and 1 kHz simulated with COMSOL Multiphysics (plain lines) and compared to the theoretical expression of equation (10) (plus markers), for different values of μ _t : (a) omnidirectional (μ _t  = 0); (b) subcardioid (μ _t  = 0.3); (c) cardioid (μ _t  = 0.5); (d) supercardioid (m u _t  = 0.63); (e) hypercardioid (μ _t  = 0.75); (f) bidirectional (μ _t  = 1).