Patent GB-244147-A (GB)
Title: Improvements in the testing and measurement of audition
Filed: 1924-08-13
Abstract: 244,147. Western Electric Co., Ltd., (Western Electric Co., Inc.). Aug. 13, 1924. Ear instruments.-A system for the testing and measurement of audition, particularly of deaf persons, comprises an electrical circuit including a source of vibratory current of adjustable frequency, a telephone receiver for detecting these currents, and an attenuator comprising series and parallel resistances for adjusting the intensity of the current, and giving upon an associated scale a direct reading of the attenuation of the currents at different frequencies. In the arrangement shown in Fig. 1, a vacuum tube oscillator 10 of adjustable frequency, is connected through an ammeter 12, an attenuator 14, and an equalizing network 16, to a telephone receiver 18. The variable attenuator 14 comprises a number of series resistances 25, and' number of shunt resistances 27. Ten taps are taken from each series resistance and connected to circularly-arranged contact-studs engaged by a brush 24, adaped to be rotated by a knob, which carries a pointer moving over a scale. An additional artificial line 32 may be introduced by throwing a change-over switch 30. The ammeter 12 is required if the oscillator 10 produces different values of currents for different frequencies. It is calibrated in units, corresponding to those used for indicating the amount of attenuation 14 included in the circuit, below an arbitrary standard value of currents, so that the total attenuation is the sum of the readings of the ammeter 12 and the indicator for the attenuator 14. Another method of correcting for unequal currents at different frequencies consists in mechanically connecting the spindle of the condenser 35, Fig. 3, used for varying the frequency, to series and shunt resistances 37, 39 arranged so as to ensure a constant current for all frequencies. This arrangement may be utilized to compensate for the variation in the response of the receiver 18 due to different frequencies, in which case the network 16 may be dispensed with. The network 16 may also be omitted if the receiver 18 is damped sufficiently to give a constant response at all frequencies in the desired range. Alternatively a chart may be employed for making these frequency corrections. In use, the system is first adjusted to produce a maximum tone for use as a standard of comparison. The ear is then tested at different frequencies note being taken in each case of the indicator reading at which the sound in the receiver becomes inaudible. The indicator shown in Figs. 4 and 5 is arranged to measure deafness taking normal bearing as a standard. The zero reading of the pointer 43 on the scale is arranged to represent threshold or minimum audibility of the normal ear, and as this point is different at different frequencies, the pointer 43 is made adjustable on the spindle carrying the knob 41 and the brush 24<1>, a spring 47 on the pointer being adapted to engage in notches 45 in the knob, and the correct frequencies being indicated opposite the notches. The frequency calibrations may also be positioned to correct any frequency irregularities in the system thus permitting the previously-described corrective devices to be dispensed with. The pointer 43 may be omitted and a visual comparison made of the two scales.