Downloaded from https://www.everyspec.com MIL-STD-81OC 3.4.2 Performance of test Step 1 - The overall sound pressure level for the specified test table S15.2-1 shall be introduced into the test chamber-to conform to the octave band spectrum specified on figure 515.2-2. The average sound pressure distribution (overall level) shall be uniform within -2 to +4 dB of the desired value. The sound pressure field shall be measured without the test item mounted in the test chamber. Measure- ments shall be made by using a microphone (more than one category of if desired) to define the sound field within the test volume (central 10 percent of the chamber volume).
Step 2 - The test item shall be placed in the chamber as specified in 3.4.1. At least three microphones shall be monitored. They shall be located in proximity to each major dissimilar test item surface, at least 18 inches from the test item surface or one-half the distance to the nearest chamber wall, whichever is less. The average overall sound pres- sure distribution around the test item shall be measured and be uniform within -2 to +4 dB of the desired value’. However, for large or irregularly shaped items where this tolerance cannot be achieved, the tolerance shall be *6 dB. Test times shall be as specified in table 515.2-1.
The operation of the test item during the test shall be monitored when and as specified. When measurements are made during or following the test, they shall be compared with the data obtained in accordance with General Require- ments, 3.2. At the conclusion of the test, the test item shall be inspected in accordance with Gbneral Requirements, 3.2. J 3.5 Procedure II acoustic testing for assembled externally carried aircraft stores 3.5.1 This acoustic test is performed to determine that the assembled store is constructed to withstand and perform in the expected dynamic environment.
Procedure IIB of Method 515.2, assembled externally carried store vibration test, shall also be conducted to insure thorough testing from 20 to 2,000 Hz. Acoustic testing of assembled externally carried , stores is not required if the minimum value of f. of 4.6.:3.2.3 of procedure 118 ~ of Method 514.2 is greater than 1,200 Hz. MSTHOD 515.2 515.2,-4