Acoustical testing of a wide range of products is performed in the National Voluntary Laboratory Accreditation Program (NVLAP) accredited laboratory (NVLAP Lab Code 100286-0) located at our headquarters in Cedar Park, Texas. In addition to standardized testing, our Acoustic Research Lab conducts customized test programs to answer client-specific product research and development needs, provide independently proven product noise emission information, and ensure product compliance requirements. We are proud of our unique distinction as the first NVLAP accredited lab in the U.S. that can provide testing per the aural non-detectability requirements specified in MIL-STD-1474E.
ETS-Lindgren’s Acoustic Research Laboratory is comprised of multiple acoustic test chambers with state-of-the-art measurement equipment and customized software. The lab uses a reverberant chamber suite for determining sound transmission loss, sound absorption, and noise isolation, and a hemi-anechoic chamber for noise emissions and sound power determinations. Our chambers are:
The ETS-Lindgren Acoustic Research Laboratory includes a precision-grade, double-walled hemi-anechoic chamber for product noise emission testing and other acoustic testing requiring an acoustic free-field environment over a reflecting plane. Equipment available for use in our chamber includes a multiple-channel data acquisition system, and high accuracy microphone and specimen positioning systems, signal generators, and reference sound sources. The chamber is qualified to ISO 26101 (Acoustics – Test methods for the qualification of free-field environments). The qualified frequency range is 63 Hz to 20 kHz to a distance of 2.5 meters.
Types of testing commonly performed in our hemi-anechoic chamber include product noise emission testing (including sound power determinations defined by ISO 3744, operator/bystander sound pressure level measurements defined by ISO 11201/ISO 7779, prominent tone evaluation, loudness calculations, and advanced sound quality analysis), waveform recording and waveform analysis. The extremely low-noise and free-field environment also allows for testing audio component frequency response, source directionality, and signal fidelity. Aural non-detectability of Department of Defense devices (per MIL-STD-1474E) is also available. The hemi-anechoic chamber is configurable for client testing requirements, including data lines, electric power, air supply/exhaust, etc. A large acoustically isolated control room adjacent to the chamber allows incorporation of any client-supplied equipment into the test program as needed.
The Reverberation Test Suite is comprised of a 408 cubic meter chamber, designated the receive room, and a 208 cubic meter chamber, designated the source room. The two rooms are connected by an operable tunnel that accommodates a single 105 inch wide by 105 inch tall test fixture that is capable of supporting test specimens that are up to 96 inches wide by 96 inches tall by 16 inches deep with many inserts to accommodate smaller specimen sizes as needed. Specimens deeper than 16 inches can be accommodated if the specimen can be broken down to 16 inches or less before placing it in between the reverberation chambers. The reverberation test suite includes a 5 ton capacity overhead bridge crane that allows for a wide variety of specimens to be transported into and out from the test area rapidly and efficiently.
The acoustic reverberation test suite at ETS-Lindgren is currently accredited to perform ASTM E90, ASTM C423, and one of 4 laboratories in the United States accredited by NVLAP to perform ASTM E596 testing utilizing our state of the art data acquisition systems. We are capable of performing large test programs with many different test specimens as part of the test program. Data for each specimen is obtained and is provided, at minimum, in the format required by the test method utilized. Additional data can be provided by request. Standard data that is provided with each specimen is the 1/3rd octave band spectrum, STC (Sound Transmission Class), OITC (Outdoor-indoor Transmission Class), Rw (Airborne Sound Reduction Index), NRC (Noise Reduction Coefficient), SAA (Sound Absorption Average), and NIC (Noise Isolation Class) based on the appropriate measurements for the test method utilized.
The Acoustic Research Laboratory at ETS-Lindgren stands ready for our men and women in uniform by being the only testing laboratory In North America accredited by NVLAP to perform MIL-STD-1474E accredited tests for aural non-detectibility. The United States Department of Defense has strict requirements for devices that soldiers utilize in the field. Among the DOD requirements is the aural non-detectibility requirement to ensure a soldier's position will not be given away by the tools the soldier utilizes to monitor, react, and report situations in the field.
The design and construction of our Hemi-Anechoic test suite ensures that our ambient noise levels inside of the test chamber remain well below 0dB from 100Hz to 20kHz. In the newest revision of 1474E chambers are additionally required to be qualified to ISO 26101 as well as the ambient noise levels described in MIL-STD-1474E. Our hemi-anechoic chamber is tested regularly to ensure conformance to the qualification standards of ISO 26101. We take great pride in knowing that we are helping to keep our soldiers out of harm’s way in the field by remaining accredited to perform this vital test.
Normal Incidence Sound Absorption testing is performed the ARL's 24 inch, 12 inch, 8 inch, and 2 inch impedance tubes. Unlike sound absorption testing performed in the reverberation room, which utilized a diffuse, random incidence field to determine the sound absorption properties of a specimen, the normal incidence method utilizes a long tube that is driven at one end by a broadband noise source (in this case pink noise). Planar waves, or sound waves with relatively flat wave fronts, are produced in the tube, and our data acquisition system is able to measure the difference between the incident wave (the sound wave traveling from the source to the specimen), and any reflected sound waves from the specimen to calculate the normal incidence sound absorption properties of the specimen.
From houses of worship to movie theaters sound absorption is utilized to control the sound quality in a space. Acousticians have several criteria that they strive to control in many different kinds of spaces. One of those criteria is reverberation time. Reverberation time, or RT60 for short, is a measure of the time it takes for a sound to reduce, or decay, by 60dB in a space. Typically the longer this time is the more difficult it becomes to discern details in the program audio that is being presented, whether that is speech, music, or a mixture of both. To be able to control the reverberation times within a space acousticians will generally add absorptive materials within the space. One of the challenges that acousticians face is the fact that reverberation times will not always be consistent over the audible frequency range, in fact most of the time they are not. Similar to random incidence absorption testing, normal incidence absorption testing allows the interested parties the ability to observe the absorption of a specimen throughout the frequency range to determine if the material would work well for an application. Random incidence absorption testing that is completed in a reverberation chamber will provide the user with data within 1/3rd octave band frequency ranges, while normal incidence testing provides data at discrete frequency steps allowing the user of the data to see the absorption of the specimen in greater detail than with random incidence absorption testing.