MIL-DTL-25547C
3.5 Voice coil polarity (see 4.6.3). When tested as specified in 4.6.3, the polarity of the voice coil shall be
determined and the positive terminal of the voice coil shall be marked with a red dot. The marking shall not interfere
with the electrical connections and shall not be impaired by soldering or unsoldering operations.
3.6 Stray magnetic field. When tested as specified in 4.6.4, the loudspeaker shall not cause a deflection of more
than 5° on a magnetic compass.
3.7 Sensitivity.
3.7.1 At sea level. When loudspeakers are tested as specified in 4.6.5.1, the average sensitivity above a reference
level of 0.0002 dyne per square centimeter for each of the indicated frequency bands, shall be not less than the values
shown in table I.
TABLE I. Sensitivity.
Frequency
Average
band
sensitivity
dB
Hz
97.0
500 - 800
102.0
800 - 1250
103.0
1250 - 2000
106.0
2000 - 3200
103.5
3200 - 5000
103.0
500 - 5000
3.7.2 At altitude. When loudspeakers are tested as specified in 4.6.5.2, the sensitivity measured at an altitude of
15,000 feet, shall not differ by more than ±3 dB from the sensitivity measured at ground level (see 4.3).
3.8 Frequency response. When loudspeakers are tested as specified in 4.6.6, the frequency response shall be
within the limits specified on figure 2, except that sharp peaks and dips may extend beyond these limits provided the
width of the extension is not greater than 0.1 octave at the limit, and the number of extensions does not exceed 1 peak
or dip per octave below 3,000 Hz, and 3 peaks or dips above 3,000 Hz.
3.9 Directional characteristics. When loudspeakers are tested as specified in 4.6.7, the sound pressure measured 4
feet away from the loudspeaker in a free field at the indicated angles in all four quadrants with respect to the principal
axis shall not deviate from the sound pressure measured on the principal axis by an amount greater than the values
shown in table II for a frequency of 1,000 Hz. The same input signal shall be applied for both on-axis and off-axis
sound pressure measurements.
TABLE II. Directional characteristics.
Maximum sound pressure
deviation (dB)
Frequency (Hz)
Off-Axis Angles
15°
30°
-6.0
-3.0
1,000
3.10 Linearity. When loudspeakers are tested as specified in 4.6.8, the acoustic output of the loudspeaker shall not
deviate from a linear function of the input voltage by more than 1 dB.
3.11 Distortion. When loudspeakers are tested as specified in 4.6.9, the harmonic distortion in the acoustic output
shall not exceed the values given in table III.
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