California Code of Regulations › Title 8 - Industrial Relations › Division 1 - Department of Industrial Relations › Chapter 4 - Division of Industrial Safety › Subchapter 7 - General Industry Safety Orders › Group 15 - Occupational Noise and Ergonomics › Article 105 - Control of Noise Exposure › Appendix D - Acoustic Calibration of Audiometers

Current through Register 2024 Notice Reg. No. 28, July 12, 2024
I. Audiometer calibration shall be checked
						  acoustically, at least annually, according to the procedures described in this
						  Appendix. The equipment necessary to perform these measurements is a sound
						  level meter, octave-band filter set, and a National Bureau of Standards 9A
						  coupler. In making these measurements, the accuracy of the calibrating
						  equipment shall be sufficient to determine that the audiometer is within the
						  tolerances permitted by ANSI S
						  3.6-1969.
(a) Sound Pressure Output Check.
(1) Place the earphone coupler over the microphone of
						  the sound level meter and place the earphone on the coupler.
(2) Set the audiometer's hearing threshold level (HTL)
						  dial to 70 dB.
(3) Measure the sound pressure level of the tones at
						  each test frequency from 500 Hz through 6000 Hz for each earphone.
(4) At each frequency the readout on the sound level
						  meter should correspond to the levels in Table D-1 or Table D-2, as
						  appropriate, for the type of earphone, in the column entitled "sound level
						  meter reading."
(b) Linearity Check.
(1) With the earphone in place, set the frequency to
						  1000 Hz and the HTL dial on the audiometer to 70 dB.
(2) Measure the sound levels in the coupler at each
						  10dB decrement from 70 dB to 10 dB, noting the sound level meter reading at
						  each setting.
(3) For each 10-dB decrement on the audiometer, the
						  sound level meter should indicate a corresponding 10 dB decrease.
(4) This measurement may be made electrically with a
						  voltmeter connected to the earphone terminals.
(c) Tolerances.
When any of the measured sound levels deviate from the
						  levels in Table D-1 or Table D-2 by 3 dB at any test frequency between 500 and
						  3000 Hz, 4 dB at 4000 Hz, or 5 dB at 6000 Hz, an exhaustive calibration is
						  advised. An exhaustive calibration is required if the deviations are 15 dB or
						  greater at any test frequency.
Table D-2
Reference Threshold Levels for
									 Telephonics TDH-39 Earphones
Frequency,
Reference
								  Threshold Level for TDH-39 Hz Earphones, dB
Sound Level Meter Reading, dB
500..........................
11.5
81.5
1000..........................
7
77
2000..........................
9
79
3000..........................
10
80
4000..........................
9.5
79.5
6000..........................
15.5
85.5
Table D-2
Reference Threshold Levels for
									 Telephonics-TDH-49 Earphones
Frequency, Hz
Reference Threshold Level for TDH-49 Earphones,
								  dB
Sound Level Meter Reading,
								  dB
500..........................
13.5
83.5
1000..........................
7.5
77.5
2000..........................
11
81.0
3000..........................
9.5
79.5
4000..........................
10.5
80.5
6000..........................
13.5
83.5
Note: Authority cited and Reference: Section
							 142.3, Labor
							 Code.