The Acoustic Lens

Author: N.H. Crowhurst

The effect of an acoustic lens

The best solution for wide ranges of frequency is the acoustic lens (a series of perforated or parallel plates). Like its counterpart in waveguide radio, it is effective above a certain limit frequency. As the ordinary horn construction, using a tractrix or similar mouth, can be effective up to a frequency where the bell ceases to have effect, the lens can be arranged to take over from there and effectively scatter all frequencies above that point.

Another system is based on the fact that high frequencies are subject to reflection by surfaces a wavelength or more in size. This method uses "deflector" plates inside a horn. The bell distributes the lower frequencies, and the deflectors take care of the higher ones.

The effect of deflector plates