Impedance and Absorption of Acoustical Materials ASTM E1050

Impedance and Absorption of Acoustical Materials ASTM E1050

ASTM E1050 test method evaluates normal incidence sound absorption coefficients and normal specific acoustic impedance ratios of materials. An impedance tube, two microphone locations, and a digital frequency analysis system are used to carry out the test. The properties measured with this Impedance and absorption test method are useful in basic research and product development of sound absorptive materials.


    ASTM E1050 test method can be applied to measure sound absorption coefficients of absorptive materials at normal incidence, that is, 0°. It can also be used to determine specific impedance and admittance ratios. 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. Estimates of the random incidence absorption coefficients can be obtained from normal impedance data for locally reacting materials.

    Test Procedure:

    The two-microphone transfer method based on the standing wave impedance tube method is mentioned in order to determine the acoustic properties, i.e. absorption coefficient, reflection coefficient, surface impedance and surface admittance. Using the ASTM E1050 test method for acoustic material testing, it is very simple and convenient to determine the normal acoustic properties. It is a very fast and accurate method to determine the acoustic properties, and is applicable in a large frequency range, as well.

    Sample size:

    Two identical impedance tubes of different  length are used to measure Impedance and Absorption of Acoustical Materials by ASTM E1050.


    The values stated in SI units are to be regarded as standard.

    Field of Application:

    Normal incidence sound absorption coefficients can be quite useful in certain situations where the material is placed within a small acoustical cavity close to a sound source, for example, a closely fitted machine enclosure. Care should be exercised to sample non uniform materials adequately.


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