Downloaded from https://www.everyspec.com MIL-STD-81OC 10 March 197S METHOD 515.2 ACOUSTICAL NOISE 1. PURPOSE. The acoustical noise test is performed to determinethe effects on e-t of fluctuating pressure fields associated with turbulent aero- dynamic flow and acoustic noise that are characteristicof aircraft,missiles, and other high-performancevehicles. The acoustical”noise test complements conventional sinusoidal and random vibration tests which are for structure borne vibrations. 2. APPARATUS. A suitable type test chamber shall be used to apply the conditions as specified in the following procedures. Measuring equipment shall be suitable to accomplish the required analysis. 3. PROCEDURE.
The basis for selecting a test procedure for a particular category shall be according to 3.1.1. 3.1 Definitions and terms. A comprehensive list of standard terminology is titled Acoustical Terminology (includingMechanical Shock and Vibration) contained in ANSI-SI.1-1960. 3.1.1 Test selection. For the purpose of this test method, equipment is categorized as follows: a. Equipment mounted either external or internal to the vehicle structure (see 3.2, 3.3, and 3.4). In general, equipment located in”areas where noise levels are 130 dB overall or less will not require testing to noise environments.
This test is not a substitute for the conventional sinusoi- dal or random vibration tests of Method 514.2. b. Assembled externally carried aircraft stores (see 3.5). This test is performed to determine if a complete store as a system is constructed to withstand its expected aerodynamic environment and to insure that performance degradations or malfunctions will not be produced by the service environment. 3.2 Criteria for application. Some equipment is insensitiveto acoustic stimulation even at very high levels. Other equipment may respond in a manner that will modify or disrupt the equipment function and in extreme cases mechanical failure may result.
Equipment that is sensitive to vibra- tion is usually sensitive to sound field exposure. For this reason a suitable vibration test is often a good indicator of acoustic sensitivity. However, it is possible that high frequency resonances of some responding equipment elements may be overlooked during the vibration test due to the 515.2-1 METHOD 515.2 10 March 1975