Acoustic Noise | Rumore acustico

MIL STD 810 G – Test Method 515.6 – Acoustic Noise

 

SCOPE

 

Purpose
The acoustic noise test is performed to determine the adequacy of materiel to resist the specified acoustic environment without unacceptable degradation of its functional performance and/or structural integrity.
Application
This test is applicable to systems, sub-systems, and units, hereafter called materiel, that must function and/or survive in a severe acoustic noise environment. This test is also applicable for materiel located where acoustic noise excitation is used in combination with, or in preference to mechanical vibration excitation for the simulation of aerodynamic turbulence (Method 523.3).
Limitations
Technical limitations restrict production and control of laboratory acoustic environments. Therefore, laboratory acoustic fields can be significantly different from many of the real fluctuating pressure loadings classed as “acoustic.” Consider these limitations when choosing a test type and test facility, as well as in interpreting test results. For example, diffuse field acoustic noise (see paragraph 2.3.3.1) better represents acoustics in internal cavities where local reflection and re-radiation from vibrating structures predominate. For external skins exposed to aerodynamic turbulence or jet noise, grazing incidence acoustic noise (see paragraph 2.3.3.2) more closely represents flow/acoustic wave propagation along skin surfaces.

 

TEST PROCESS

 

Procedure 1 – Diffuse field acoustic noise testing
  • Step 1. Install the test item in the reverberation chamber in accordance with paragraph 4.5.2.
  • Step 2. Select microphone positions for control, monitoring, and control strategy in accordance with paragraph 4.5.1.1.
  • Step 3. When using open loop control, remove the test item and confirm the specified overall sound pressure level and spectrum can be achieved in an empty chamber, then replace the test item in the chamber.
  • Step 4. Precondition the test item in accordance with paragraph 4.5.1.2.
  • Step 5. Conduct initial checks in accordance with paragraph 4.5.1.2.
  • Step 6. Apply the test spectrum for the specified time. If required, carry out inspections and operational checks in accordance with paragraph 4.5.1.2. If the test item fails to operate as intended, follow the guidance in paragraph 4.3.2 for test item failure.
  • Step 7. Record the test acoustic field at each microphone, any average used in test control, and other pertinent transducer outputs. Make the recordings at the beginning, midpoint, and end of each test run. Where test runs are longer than one hour, record every one-half hour.
  • Step 8. Carry out the final inspection and operational checks, and see paragraph 5 for analysis of results.
  • Step 9. Remove the test item from the chamber.
  • Step 10. In all cases, record the information required.
Procedure 2 – Grazing incidence acoustic noise testing
  • Step 1. Install the test item in accordance with paragraph 4.5.2.
  • Step 2. Select microphone positions for control, monitoring, and control strategy in accordance with paragraph 4.5.2.1.
  • Step 3. Precondition the test item in accordance with paragraph 4.5.1.2.
  • Step 4. Conduct initial checks in accordance with paragraph 4.5.1.2.
  • Step 5. Apply the test spectrum for the specified time. If required, carry out inspections and operational checks in accordance with paragraph 4.5.1.2. If the test item fails to operate as intended, follow the guidance in paragraph 4.3.2 for test item failure.
  • Step 6. Record the test acoustic field at each microphone, any average used in test control, and other pertinent transducer outputs. Make recordings at the beginning, end and midpoint of each test run. Where test runs are longer than one hour, record every one-half hour.
  • Step 7. Carry out the final inspection and operational checks, and see paragraph 5 for analysis of results..
  • Step 8. Remove the test item from the duct.
  • Step 9. In all cases, record the information required.
Procedure 3 – Cavity resonance acoustic noise testing
  • Step 1. Install the test item into the chamber in accordance with paragraph 4.5.2.
  • Step 2. Locate the control microphone in accordance with paragraph 4.5.2.1.
  • Step 3. Precondition the test item in accordance with paragraph 4.5.1.2.
  • Step 4. Conduct initial checks in accordance with paragraph 4.5.1.2.
  • Step 5. Apply the sinusoidal acoustic excitation at the required frequencies (see Table 515.6A-II). Adjust the test parameters to the specified levels and apply for the specified time. If required, carry out inspections and operational checks in accordance with paragraph 4.5.1.2. If the test item fails to operate as intended, follow the guidance in paragraph 4.3.2 for test item failure.
  • Step 6. Record the test acoustic field at each microphone, any average used in test control, and other pertinent transducer outputs. Make recordings at the beginning, midpoint, and end of each test run. Where test runs are longer than one hour, record every one-half hour.
  • Step 7. Perform the final physical inspection and operational checks, and see paragraph 5 for analysis of results..
  • Step 8. Remove the test item from the chamber.
  • Step 9. In all cases, record the information required.

 

NOTE: Tailoring is essential. Please, ask to your confidence laboratory for further details about tailoring of test methods.

 

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