MIL-DTL-5589E
the vacuum tube voltmeter (VTVM No. 1). For first article inspection, the frequency response shall be
measured and recorded in accordance with 4.6.2.1. For conformance inspection the frequency response
shall be measured and recorded in accordance with 4.6.2.1 or 4.6.2.2, at the option of the supplier.
4.6.2.1 Automatic recorder. The acoustic output shall be recorded on a direct writing strip graph using
an automatic plotter or curve tracer with a minimum writing speed of 10 inches per second and a
maximum chart speed of 30 inches per minute. The output shall be recorded in the dB value above
0.0002 dyne per square centimeter. The writing speed and chart speed shall be noted.
4.6.2.2 Point to point. Measure the acoustic output from the calibrated microphone and preamplifier
unit as indicated by the reading of VTVM No. 2 (see figure 2), and convert this reading to the equivalent
dB value above 0.0002 dyne per square centimeter, using the most recent available calibration curve for
the test microphone. Measure and record the dB increments of 100 Hz from 100 Hz to 1,000 Hz and at
increments of 250 Hz from 1,000 Hz to 8,000 Hz. The graph shall show the dB values on the ordinate
scale, reading from 80 dB to 140 dB above 0.0002 dyne per square centimeter, and the Hz value on the
abscissa scale, reading from 100 Hz to 10,000 Hz inclusive.
4.6.3 Impedance (see 3.4.2). Impedance measurements shall be made at 1,000 Hz with the earphone
mounted on the coupler as shown on figure 2. The 1,000 Hz voltage applied across the terminals of the
earphone element during impedance measurements shall be between 0.9 and 1.3 volts rms. The
impedance shall be measured by measuring the voltage across and the current through the earphone.
4.6.3.1 Voltage method. At the option of the manufacturer, the impedance may be calculated by
using a voltmeter. Using a circuit similar to that shown on figure 2, measure the voltage across the 300
ohm resistor and across the earphone under test. The earphone impedance (z) is equal to
VB
300 X
Va - Vb
4.6.4 Harmonic distortion (see 3.4.3). The earphone shall be tested while connected to the test circuit
and mounted on the coupler as shown on figure 2. Distortion shall be measured at 200 Hz and at
frequencies between 400 Hz and 7,000 Hz, as are required to determine at what frequencies (in this
range) maximum distortion exists.
4.6.4.1 Distortion analyzer. The total harmonic distortion shall be determined by a distortion analyzer,
having the following minimum requirements:
a. Frequency range: Fundamental frequency from 20 Hz to 20,000 Hz.
b. Frequency calibration: ±2 percent from 20 Hz to 20,000 Hz.
c. Harmonic measurement: ±3 percent of full scale value for distortion levels as low as 0.5
percent.
4.6.5 Dielectric withstanding voltage (see 3.4.4). The earphone shall be tested in accordance with
method 301 of MIL-STD-202. The following details shall apply:
a. Test voltage: 500 volts.
b. Nature of potential: 60 Hz.
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