A new technique for the measurement of the normal incidence absorption coefficient using an impedance tube and a single microphone with fixed position

2008 ◽  
Vol 123 (5) ◽  
pp. 3500-3500
Author(s):  
Cedric Vuye ◽  
Steve Vanlanduit ◽  
Karl Van Nieuwenhuyse ◽  
Patrick Guillaume
Keyword(s):  
Absorption Coefficient ◽  
Normal Incidence ◽  
New Technique ◽  
Fixed Position ◽  
Impedance Tube ◽  
A New Technique

Sound Absorption Characteristics of Porous Steel Manufactured by Lost Carbonate Sintering

2009 ◽  
Vol 1188 ◽  
Author(s):  
Miao Lu ◽  
Carl Hopkins ◽  
Yuyuan Zhao ◽  
Gary Seiffert
Keyword(s):  
Absorption Coefficient ◽  
Pore Size ◽  
Sound Absorption ◽  
Single Layer ◽  
Normal Incidence ◽  
Sound Absorption Coefficient ◽  
Absorption Coefficients ◽  
Impedance Tube ◽  
Absorption Characteristics

AbstractThis paper investigates the sound absorption characteristics of porous steel samples manufactured by Lost Carbonate Sintering. Measurements of the normal incidence sound absorption coefficient were made using an impedance tube for single-layer porous steel discs and assemblies comprising four layers of porous steel discs. The sound absorption coefficient was found not to vary significantly with pore size in the range of 250-1500 μm. In general, the absorption coefficient increases with increasing frequency and increasing thickness, and peaks at specific frequencies depending on the porosity. An increase in porosity tends to increase the frequency at which the sound absorption coefficient reaches this peak. An advantage was found in using an assembly of samples with gradient porosities of 75%-70%-65%-60% as it gave higher and more uniform sound absorption coefficients than an assembly with porosities of 75%.

Measurement Signal Effects on the Normal-Incidence Absorption Coefficient

Volume 1 ◽  
2004 ◽  
Author(s):  
Kuang-Yih Tsuei ◽  
Wen-Wang Jiang ◽  
Shu-Fen Kuo
Keyword(s):  
Plane Wave ◽  
Absorption Coefficient ◽  
Coherence Function ◽  
Normal Incidence ◽  
Measurement Procedure ◽  
Test System ◽  
Test Method ◽  
Impedance Tube ◽  
Measurement Results ◽  
Measurement Signal

This paper will demonstrate the signal effects on the normal-incidence absorption coefficient. The test method covers two microphones located in impedance tube to measure this coefficient. It should analyze the measurement procedure and formulae theoretically, furthermore to propose the coherence function as the criteria for measurement results. Experimentally, different signals, generated by a sound source, input to the loudspeaker in impedance tube to produce the plane wave and two microphones can measure the sound pressures. Through different time weightings and average times on the two microphone signals, and after analyzing results of the frequency response, the coherence function and the normal-incidence absorption coefficient, the coherence function is a major factor to check the normal-incidence absorption coefficient reliable, even the test system stable or not.

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