Measurement of the sound-absorption coefficient in situ: The reflection method using periodic pseudo-random sequences of maximum length

The accuracy of a method [Wijnant et al., Proc. of ISMA 31, Leuven, Belgium (2010), Vol. 31] for measurement of the effective area-averaged in situ sound absorption coefficient is investigated. Based on a local plane wave assumption, this method can be applied to sound fields for which a model is not available. Investigations were carried out by means of finite element simulations for a typical case. The results show that the method is a promising method for determining the effective area-averaged in situ sound absorption coefficient in complex sound fields.

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“…(6). After completion of a series of point measurements, the incident sound intensity distribution over S 0 is obtained.…”

Section: Theorymentioning

confidence: 99%

“…[1][2][3][4][5] Exceptions are methods that employ a time-windowing technique. [6][7][8] However, in small enclosures, measurements at low frequencies cannot be performed as the length of the time window needs to be very short to gate out spurious reflections.…”

Section: Introductionmentioning

confidence: 99%

A numerical study of a method for measuring the effective in situ sound absorption coefficient

Kuipers

Wijnant

Boer

2012

The Journal of the Acoustical Society of America

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“…It will be referred to as the reference model hereafter.An umber of methods [5,6,7,8] assume plane wave incidence, whereas other methods consider spherical wave incidence [9,10,11,12,13,14,15,16]. Adifferent approach is applied in the in situ method by Takahashi et al [7], further studied by Otsuru [17], and Din [8].…”

Section: Introductionmentioning

confidence: 99%

“…The first cause for such ad eviation may be the presence of reflections other than from the specimen, such as room reflections. Astrategytoeliminate these, is to gate these so-called parasitic or spurious reflections out from the impulse response by employing atime-windowing technique [9,10,11,12,16]. Formethods that do not use an impulse response, one may place the source near the surface [18] so that the relative amplitudes of the unwanted reflections are reduced.…”

Section: Introductionmentioning

confidence: 99%

Measuring Sound Absorption: Considerations on the Measurement of the Active Acoustic Power

Kuipers¹,

Wijnant²,

Boer³

2014

Acta Acustica united with Acustica

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SummaryUsing alocal plane wave assumption, one can determine the normal incidence sound absorption coefficient of a surface by measuring the acoustic pressure and the particle velocity normal to that surface. As the measurement surface lies in front of the material surface, the measured active and incident acoustic power will generally deviate from those at the material surface, leading to ap ossibly inaccurate sound absorption coefficient. This phenomenon is particularly pronounced for poorly absorbing surfaces if sound is not normally incident overthe whole material surface. Based on an analytical model, it is shown that the accuracycan be improvedbyextending the measurement surface upon which the active acoustic power is measured. Experimental results demonstrate the usefulness of this approach, in particular for poorly absorbing surfaces.

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“…Multiple methods [3,4,5,6,7,8,9,10] can be applied to determine the oblique incidence sound absorption coefficient. These methods mostly determine the specific acoustic surface impedance or the complex sound pressure reflection coefficient, using a model that typically describes the overall acoustic field in front of a planar surface of infinite extent in a semi-free field.…”

Section: Introductionmentioning

confidence: 99%

Measuring oblique incidence sound absorption using a local plane wave assumption

Kuipers¹,

Wijnant²,

Boer³

2014

Acta Acustica united with Acustica

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SummaryIn this paper a method for the measurement of the oblique incidence sound absorption coefficient is presented. It is based on a local field assumption, in which the acoustic field is locally approximated by one incident-and one specularly reflected plane wave. The amplitudes of these waves can be determined with an unidirectional sound intensity probe. The local active-and incident acoustic intensity are straightforwardly obtained. The area-averaged sound absorption coefficient is calculated after spatial integration of these quantities over the surface area of interest. Alternatively, one may use a three-dimensional intensity probe. In that case, the determination of the amplitudes of the plane waves can be formulated as a least-squares problem. Measurements performed for a sound absorbing foam demonstrate that accurate results can be obtained, even under non-ideal acoustic conditions. Measurements carried out for a periodic absorber show that the method is accurate below the cuton frequency of scattering as long as the amplitude of the evanescent surface waves is significantly smaller than that of the specularly reflected wave. PACS no. 43.20El, 43.55Ev, 43.55Dt

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Measurement of the sound-absorption coefficient in situ: The reflection method using periodic pseudo-random sequences of maximum length

Cited by 81 publications

References 17 publications

A numerical study of a method for measuring the effective in situ sound absorption coefficient

A numerical study of a method for measuring the effective in situ sound absorption coefficient

Measuring Sound Absorption: Considerations on the Measurement of the Active Acoustic Power

Measuring oblique incidence sound absorption using a local plane wave assumption

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