Downloaded from https://www.everyspec.com MIL-STD-81OD 19 July 1983 (2) Assembled externally-carried stores (3) Ground support equipment on the flightline Acouetic testing “is performed if the operational acoustic level exceeds 135 dB or vibration testing ie impractical. b. ~. This method is not applicable to space and water .vehicleeand is not for hearing safety.’ Nor is it “applicableto items which, because of their construction, are insensitive“to acoustic noise. Examples of such equipment are items that have small surfaoes, high ratioa of maas-to-area, and high internal damping. Examplee are (1) high density modtilee,particular y ?.
‘if they are encapsulated and (2) equipment that is surrounded by a he,avymetal caee, particularly if the equipment is potted. A practioal guideline is that acoustic tests are not required if equipment is exposed to broadband random noise at a sound.preseuqe level leas than 130 decibels (ref 20 !.’Pa)overall, and if its exposure in every one-Hertz band is less than 100 decibele (ref 20 u Pa). -. .. c. ~. Acoustic testing may be performed anywhere in the test procese.
The accumulated effects of acoustic atress may affect equipment performance under other environmental conditions, euch aa temperature, altitude, humidity, or EMI/EMC.“ When it ia desired to evaluate the cumulative environmental effects of acouetic noise (paragraph I-2) and other environments, a eingle teet item should be exposed to all environmental conditions, with acouatic noise testing performed firet. d. XfietvariaLL9mi .(1) ~a. This “method is composed of four procedures -. the environmental worthiness test, the qualification teet, the mission”profile test, and the cavity resonance test. (2) leet c~. Within eaoh procedure, values muet be assigned to the following variables:
(a) Sound spectrum (b) Dynamic pressure level (c) Duration (d) Tolerances or jet engine. Acouetic excitation’field -- reverberant, pr0gre9sive wave, I-3.1 ~. The choice of test procedure(e) depends on: a. The stage of the item in the design process. b. Whether or not accelerated teeting is desired. c. Whether an open cavity on an aircraft or aircraft.store is involved. METHOD 515.3 1 19 July 1983 515.3-2