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

6.15. Directivity characteristics

The response curve of Fig. 6.7 and the information of the previous three paragraphs reveal that above the frequency where ka   =   2 (usually between 800 and 2000   Hz), a direct-radiator loudspeaker can be expected to radiate less and less power. The rate at which the radiated power would decrease, if the cone were a rigid piston, is between 6 and 12   dB for each doubling of frequency. This decrease in power output is not as apparent directly in front of the loudspeaker as at the sides because of directivity. That is to say, at high frequencies, the cone directs a larger proportion of the power along the axis than in other directions. In addition, the decrease in power is overcome in part by the resonances ...