ASTM E1050: Standard Test Method for Impedance and Absorption of Acoustical Materials Using a Tube, Two Microphones and a Digital Frequency Analysis System
Standard: ASTM E1050 – Standard Test Method for Impedance and Absorption of Acoustical Materials Using a Tube, Two Microphones and a Digital Frequency Analysis System
Certification Required: The ASTM E1050 test is currently not required by building codes but it is used for research and development purposes to determine the acoustical performance of sound absorptive products. This small scale test method is specified by some automotive manufacturers and the products may need to meet minimum sound absorption coefficient requirements.
Scope: This test method covers the use of an impedance tube, two microphones, and a digital frequency analysis system for the determination of normal incidence sound absorption coefficients and normal specific acoustic impedance ratios of materials. This test method allows one to compare relative values of sound absorption when it is impractical to procure large samples for accurate random-incidence measurements in a reverberation room.
Applicable Products: This test method is applicable for hood liners, headliners, fiberglass, mineral fiber and cellulose boards or blankets, as well as other fibrous materials. It also applicable for foam products, facing materials, fabrics, papers and screens. The test apparatus will accommodate 100 mm diameter samples up to 6” thick.
Test Procedure: This test method describes how to measure the normal incidence sound absorption of acoustical products in an impedance tube. The impedance tube apparatus consists of a tube with two microphones mounted in the side wall, a speaker attached to one end and a sample holder attached to the other end. The 100 mm diameter tube is used to make measurements in the frequency range of 50 to 1,600 Hertz. The 57 mm diameter tube is used to make measurements in the frequency range of 200 to 3,150 Hertz. The 29 mm diameter tube is used to make measurements in the frequency range of 500 to 6300 Hertz. The test specimens are cut so that they fit snugly into the sample holder. The samples can be placed directly against the backing plate or the backing plate can be adjusted to provide an air space behind the test specimen. Broadband sound is then generated in the tube. The amplitude and phase of the sound is measured by the microphones and a two-channel Fast Fourier Transform (FFT) analyzer. Three test specimens from each product are tested and then the results are averaged.
End Result: The individual test datasheets can be provided for R&D purposes or a formal test report can be generated which will include the individual and average sound absorption coefficients at the standard 1/3 octave band frequencies.
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