Perception of Square-Wave and Sinusoidal-Wave Response from Direct-Radiator Subminiature Loudspeaker

Abstract

The operation of a portable counter requires the audible perception of square-wave impulses covering the 300–3000-Hz band; weight and size limitations indicate the use of a reproducer weighing only a few grams; and safety to the ear precludes the use of a hearing-aid type ear insert. These specifications appear mutually contradictory unless it is noted that the rich harmonic content of square waves may make possible the identification of relatively low frequencies by perception of the harmonics. Thus, to perceive a 300-Hz signal it may be necessary only to hear actually a 600- or 1200-Hz sine wave. A practical solution is to utilize a hearing-aid type button receiver, with the fundamental resonance of the diaphragm and associated acoustical network located at as low frequency as possible, i.e., around 1200 Hz. Free-space measurements show response from below 1000 to above 4000 Hz. It is found experimentally that this meets the above requirements. Refinements on the systems will be described.