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Fast Accurate Non-Destructive Measurement of Absorber Impedance and Absorption
ISSN: 0148-7191, e-ISSN: 2688-3627
Published June 5, 2019 by SAE International in United States
Annotation ability available
Cabin acoustic comfort is a major contributor to the potential sales success of new aircraft, cars, trucks, and trains. Recent design challenges have included the increased use of composites, and the switch to electrically powered vehicles, each of which change the interior noise spectral content and level. The role of acoustic absorption in cabins is key to the optimisation of cabin acoustic comfort for modern vehicles, with acoustic impedance data needed in order to assess and optimise the impact of each component of a given lay-up.
Measurements of absorbing interior trim are traditionally performed using either sample holder tests in a static impedance tube (impedance and absorption), or through tests in reverberation rooms (absorption only). Both of these procedures present challenges. In-tube absorption and impedance measurements are destructive, requiring highly accurate sample cutting and sealing. Reverberation room absorption measurements are subject to the effects of varying room diffusion, along with the impact of edge diffraction, sample geometry, and location. Finally, while non-destructive methods using hand-held probes also measure absorption, they are not able to measure impedance accurately.
This paper describes fast non-destructive tests using a portable flanged impedance tube, and how they be used to quantify and optimise the absorption of interior trims. Measurements are made on non-locally reacting lay-ups, with the results corrected to equivalent in-tube results using a flanged-to-sample holder correction factor. The corrected flanged tube results are then compared with baseline in-tube measurements. Discussions address data quality and how the non-destructive measurements may be used to optimise lay-ups for increased absorption.
CitationMurray, P., Alexander, J., Kunio, J., and Larsen, F., "Fast Accurate Non-Destructive Measurement of Absorber Impedance and Absorption," SAE Technical Paper 2019-01-1584, 2019, https://doi.org/10.4271/2019-01-1584.
- ASTM C423-09a, “Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method.”
- ISO 354:2003, “Acoustics - Measurement of Sound Absorption in a Reverberation Room.”
- ASTM E1050-12, “Standard Test Method for Impedance and Absorption of Acoustical Materials Using a Tube, Two Microphones, and a Digital Frequency Analysis System.”
- ISO 10534-2, “Acoustics - Determination of Sound Absorption Coefficient and Impedance in Impedance Tubes - Part 2: Transfer-Function Method.”
- Kunio, J., Yoo, T., Hoo, K., and Enok, J., “A Comparison of Two and Four Microphone Standing Wave Tube Procedures for Estimating the Normal Incidence Absorption Coefficient,” in Internoise, Aug. 2009.
- CEN/TS 1793-5:2003, “Road Traffic Noise Reducing Devices - Testing Method for Determining the Acoustic Performance - Part 5: Intrinsic Characteristics - In Situ Values of Sound Reflection and Airborne Sound Insulation.”
- Tijs, E. and Druyvesteyn, E., “An Intensity Method for Measuring Absorption Properties In Situ,” in ACTA ACUSTICA, 98, 2012.
- Jambrošić, K., Suhanek, M., and Petošić, A., “Comparison of Two Methods for In-Situ Measurement of the Absorption Coefficient,” in EURONOISE, Oct. 2009.
- Barnard, A.R. and Rao, M.D., “A Comparison of Acoustic Absorption Coefficient Measurements from the In-Situ Method with Traditional Methods,” in NOISE-CON, July 2004.
- Murray, P., Kunio, J., Christensen, L., and Larsen, F., “Use of a Portable Flanged Impedance Tube for Absorber Design and Measurement,” SAE Technical Paper 2015-01-2201, 2015, doi:10.4271/2015-01-2201.