1703 Recording Audiometer
1. Independent testing of both ears at seven frequencies The 1703 automatically presents seven pure-tone signals successively — 500, 1000, 2000, 3000, 4000, 6000 and 8000 Hz, each sustained for 30 seconds. This sequence is presented first to the subject's left ear, then automatically switched and repeated for the right ear. When the test signal is switched between ears, the signal automatically decreases to -10 dB HTL before the new test begins, a precaution which ensures that the right ear will not receive a tone at the quite possibly elevated level required by the left ear at 8 kHz. 2. Automatic retest at 1 kHz After both ears have been tested at all seven frequencies, the 1703 automatically re-presents a 1 khz tone to the right ear. The comparison of the subject's threshold during this retest tone with that recorded under the previous 1 kHz signal provides a useful indication of the test reliability. 3. Bekesy-type measurement of hearing acuity As long as the subject indicates that he hears the signal, its intensity is continuously decreased: the moment he indicates that he no longer hears the signal, its intensity is increased. This procedure is implemented through a handswitch electrically connected to the intensity drive circuit in the 1703. Pressing the switch causes the intensity to decrease. The result is that the subject, instructed to keep the tone at a level he can just hear (“Press when you hear the signal; release when you don’t.’’), regulates the intensity of the signal and tracks his own threshold. Such a threshold tracking technique is simple enough for even naive subjects to use, and provides a stable, repeatable indication of hearing acuity. 4. Variable intensity change rate In addition to controlling the direction of attenuation, the subject’s responses also determine the rate of attenuation. At the start of each test frequency, the sound level is changed more rapidly (10 dB/sec) than it is after the subject's approximate hearing threshold is reached (2.5 dB/sec.) Moreover, if 5 seconds elapse without a subject response, the attenuator rate speeds up to minimize time lost in regaining the threshold region. The result of both of these speed regulators is the rapid attainment of the subject's threshold, with minimum time spent at intensity levels unmeaningfully above or below the threshold. The effect of this procedure is a reliable, repeatable definition of the individual’s threshold. 5. Permanent record of the subject’s hearing The same circuitry which presents the signal to the subject also works, through an X-Y recorder integral to the 1703, to provide a graphic representation of the subject's threshold across all frequencies. A specially designed audiogram form placed on the recorder has a vertical axis corresponding to intensity of the signal from -10 dB to -90 dB Hearing Level.
From left to right the project team consisted of Jack Goldberg, Rick Issacs, Jack Propsma, Ben DeRuzzo, Warren Hills, Joseph Mihaly, Don Spinney and John Andrews.
