GB1185064A - Apparatus for the Testing and Treatment of Hearing Deficiencies - Google Patents

Abstract

1,185,064. Testing and treating hearing; amplifying circuits. M. S. DEMAREE. 16 Aug., 1967 [31 Oct., 1966], No. 37724/67. Headings H3W and H4J. In apparatus for testing and treating a hearing defect, a plurality of sound signals having distinct frequencies within the audio frequency range is produced sequentially, the magnitude of each of the plurality of sound signals is adjusted so that the patient has the sensation of substantially normal hearing, and the apparatus then provides for mixing signals over the entire audio frequency range. The apparatus (Fig. 4) comprises a cabinet 10 having a well 11 for storing a microphone 12 and earphones 13. A front panel 14 includes a volume control 15, an attenuator 16, a calibrator 17, a power switch 18, a meter 19 indicating the level of the incoming signal and attenuator controls 20 mounted to move in slots 21. Horizontal lines 22 indicate in dB the attentuation in each control 20, maximum attenuation being provided in the lowest position. A key card 23 (Fig. 1) has nine frequency values at which the patient's minimum sound perception level is determined and a graph is plotted by dots in boxes at frequency values of 250, 500 . . . &c., c/s. A curve (25), Fig. 2 (not shown) is drawn connecting the dots and the key card 23 is cut along the curve (25). The lower portion (27) of the key card 23 is inserted in a holder 31 of the apparatus and the attentuator controls 20 are brought downwardly until they engage the upper surface (29) of the card portion (27), thereby setting the attentuator controls 20. The patient then hears speech and music through the earphones 13 substantially normally. The attentuator 16 and volume control 15 permit the sound to reach a sufficient level to allow persons formerly considered stone deaf to hear adequately. Circuit.-Seven band pass filters 100 (Fig. 5) have centre frequencies set approximately one octave apart at 250 c/s., 500 c/s. . . . &c. A microphone 112 is coupled into a pre-amplifier 111, the output of which is connected to a master volume control 115. A VU meter 119 is connected to the output of an amplifier 117, and the output of amplifier 117 connects to one terminal of a stepped attentuator 116, the other terminal of which is connected to a common input line 118. Resistors 121 couple to the input terminals 122 of the filters 100. Further resistors 123 provide bias for the filters 100. The output of each filter 100 couples to a voltage divider 120 and this connects with the attentuator control 20 (Fig. 4). The voltage divider outputs are coupled to a power amplifier 125, the output of which is coupled directly to a headphone jack 113. A power supply 114 is provided.