Patent GB-604357-A (GB)
Title: Improvements in apparatus for measuring, or for measuring and compensating for, hearing-loss
IPC: H04R29/00
Filed: 1944-11-28
Abstract: 604,357. Audiometers. HORVITCH, G. M. Nov. 28, 1944, No. 23749. [Class 81(ii)] [Also in Groups XIX and XXXIX] In an apparatus for measuring, or for measuring and compensating for hearing loss, the plotting of the loss at selected frequencies is made directly on the chart by a marking device actuated by a neuroreaction meter applied to the patient, that is, in accordance with the variation of his nervous condition brought about by his first hearing the note being transmitted. In Fig. 1, a variable frequency generator 4 is mechanically coupled to a frequency impulse transmitter 3; each successive movement of the contact arm 3b thereof corresponds to a frequency change of lOOc/sec. and transmits an impulse to relay 11 which moves the chart through a corresponding sub-division. The signal generated is taken via a volume correction adjuster 5 to a volume control 12a; each successive movement of the control member is mechanically transmitted to the movable contact arm 12d of a volume impulse transmitter 12b, an impulse being transmitted to relay 14 which moves the chart through a corresponding subdivision. The signal is amplified in amplifier 54. The secondary of the output transformer is provided with a number of tapping points 58 for variation of the impedance. A volume level indicator comprises a rectifying valve 62 connected through condenser 65 and stabilizing resistance 64 to a rectifying valve 63, the cathode of which is connected to a milli- or micro-ammeter 67 shunted by condenser 68 and variable resistance 68a. Switch 60 is connected to tapping points 69, 69a, each connected to a head phone 73 through attenuator 87, and a resonant filter 74, which is a band pass filter and a low and higher rejection filter, or a band reject filter 85, these filters being under the control of switch 79, 80. In operation, when the patient first hears the signal, the volume of which is progressively increased by control 12a, a neuro-voltmeter 28 records his nervous reaction, thereby energising through valve 26 a relay 25, and thereby the solenoid 20 which causes a marker to make an impression on the chart. Independently, he may also manually operate key 23 to energise the solenoid. If desired, means may be provided for operating the frequency and volume control sets automatically in accordance with the operation of the marking device. The apparatus also comprises a microphone 29 and gramophone pick-up 34, each with its amplifier 30, 35 and volume control 32, 37, switch means 39 for connecting either the microphone or pickup to a further switch 41 connecting either with a resonant high- and low-pass filter 44 with a variable band width and position, or with a rejection filter 47 of variable band width and position, and thence to switch 7. Thus, sound suited to the hearing characteristics of various individuals may be transmitted. A unit 105 containing band-pass, band-reject low-pass and highpass variable filters may also be used. The chart marking device, Fig. 2, comprises a drum 88 rotatably mounted on spindle 89 which in turn is rotatable in stand 90. On rotation of spindle 89 by the frequency rotary relay 11 the drum is moved parallel to its axis by the engagement of screw 91 with nut 92 secured to the drum. On rotation of worm 97, by the volume rotary relay 14, the drum is rotated through worm wheel 96 and driving pins 95. The chart 98 secured to the drum is thus moved along its frequency ordinates 100 and volume abscissae 101 relative to the punch or marker 102, the solenoid 20 of which is shown.