Testing that Reaches the World

 MIL-STD-810, Method 515, covers acoustic noise testing for equipment. Clark testing conducts MIL-STD-810G, Method 515, to evaluate equipment's performance and suitability in environments with high levels of acoustic noise. The purpose of acoustic noise testing is to assess the equipment's ability to withstand and operate in environments with high levels of acoustic noise, such as industrial or military settings.  Clark Testing can help to identify potential issues related to noise-induced failures, degradation of performance, and adverse effects on human operators or nearby equipment. 

Method 515.6 provides detailed procedures for conducting acoustic noise testing that typically involves subjecting the equipment to controlled levels of acoustic noise generated in an acoustic chamber or other test facilities. The noise levels, frequency range, and exposure duration are specified based on the equipment's intended use and the expected noise conditions.

This test is applicable to systems, sub-systems, and units that must function and/or survive in a severe acoustic noise environment. This test is also applicable for equipment located where acoustic noise excitation is used in combination with, or in preference to mechanical vibration for the simulation of aerodynamic turbulence. 

Like vibration impact, the effects of acoustically induced stresses may affect equipment’s performance under other environmental conditions, such as temperature, humidity, pressure, electromagnetic, etc. When it is required to evaluate the effects of acoustic noise together with other environments, and when a combined test is impractical, expose a single test item to all relevant environmental conditions in turn. Consider an order of application of the tests that is compatible with the Life Cycle Environmental Profile (LCEP) and sequence guidance in the individual methods. 

MIL-STD-810G defines the noise conditions for testing, including the desired noise level and frequency range. The specific noise conditions are determined based on the equipment's intended use and the anticipated noise exposure scenarios. These conditions may include steady-state noise, impulsive noise, or a combination of both. 

The standard also defines acceptance criteria for acoustic noise testing including allowable noise-induced degradation in performance, adherence to specified performance requirements, and other factors related to the equipment's functionality and human factors considerations. The equipment is assessed based on its ability to operate effectively within the specified noise conditions.  

PROCEDURES. 

MIL-STD-810 Method 515 includes three acoustic noise test procedures. While all procedures involve acoustic noise, they differ on the basis of how the acoustic noise fluctuating pressure is generated and transferred to the equipment. 

1. Procedure I – Diffuse Field Acoustic Noise. Procedure I has a uniform intensity shaped spectrum of acoustic noise that impacts all the exposed materiel surfaces.
2. Procedure II – Grazing Incidence Acoustic Noise. Procedure II includes a high intensity, rapidly fluctuating acoustic noise with a shaped spectrum that impacts the materiel surfaces in a particular direction – generally along the long dimension of the equipment.
3. Procedure III – Cavity Resonance Acoustic Noise. In Procedure III, the intensity and, to a great extent, the frequency content of the acoustic noise spectrum is governed by the relationship between the geometrical configuration of the cavity and the equipment within the cavity.

TEST PROCESS. 

Regarding the test process, it is important to select a test facility that has the appropriate chambers and instrumentation to perform the acoustic test including sufficient capacity to reproduce the input requirements.  Test equipment that produces uniform acoustic noise tests in the field above 165 dB are rare. Therefore, for high level acoustic input (above 165 dB), consider testing using grazing incidence acoustic noise. For measured data that indicates tonal input, consider a facility that can be configured to produce a cavity resonance condition. 

The control set up depends upon the type of test and the size of the equipment.  There can be single point control or multiple point control in the chamber.  Clark’s test engineers will define the single point, providing an optimum control position in the chamber or progressive wave tube.  For multiple point noise control, we select the control points to define a controlled volume within the reverberation chamber and base the controls upon the average of the sound spectrum levels at each microphone. Where the range of measurements at the monitoring 

Where it is necessary to achieve a given vibration acceleration response on the test item, we will adjust the acoustic test spectrum to achieve the required response that may be monitored at a single point or as the average from multiple monitoring points. Refer to Method 514  for further guidance. 

Contact the test engineering team at Clark Testing to ensure your equipment will function and maintain its performance while operating in an accelerated noise environment.  Call or email the Clark Dynamics Test Laboratory for assistance in developing a test plan and conducting the appropriate test to validate your equipment in accordance with MIL-STD-810 Method 515.