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Amplivox binaural deaf aid. Separate microphones and amplifiers are associated with each earpiece.
Excellent as is the performance of the modern single-microphone deaf aid from the point of view of quality of reproduction, there must inevitably be something missing comparison with ordinary listening where there are minute differences of intensity and phase at the two ears.
To simulate the conditions of normal binaural hearing, Amplivox, Ltd., 106, George Street, London, W1, have developed a deaf aid in which entirely separate microphone-amplifier-earphone channels, are provided for each ear. Each amplifier consists of three stages, and the microphones are of the piezo-electric type. These are provided with independent volume controls and are disposed on opposite panels of a case measuring less than 12 × 3.75 × 4.75 inches. The HT and LT batteries are-housed in a central compartment, and when it is realised that space must be found in addition for no fewer than six valves and their associated components, the reduction of the overall dimensions to the figures given must be regarded as no mean achievement.
We have had an opportunity of testing this instrument under a variety of conditions and there can be little doubt that it marks a distinct advance over ordinary monaural deaf aids, The directional effect at distances up to five or six feet is most striking, and it is easy for a person blindfolded to point to the exact position occupied by a speaker as he moves about the room.
The directional properties of the instrument do not, however, exhaust its virtues, There is less confusion from room reverberations with binaural listening and a general improvement in naturalness. This is easily proved by starting with one earpiece only and then bringing in the other by turning up the volume control.
The 2-Volt accumulator supplying the filament current to the miniature valves gives 20 hours service on a charge, and the HT battery life is of the order of two months. We understand that the price of the complete instrument is 30 guineas.
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