Analysis methods for acoustical systems based on the FFT and intensity techniques

Dissertation

Tapio Lahti

Research output: ThesisDissertationMonograph

Abstract

A two-part study on the measurement and analysis of acoustical systems is presented, consisting of the development of various new methods based on the FFT and intensity, and a collection of experiments for testing their applicability.The common factor in the studies is the FFT: the measurements were made with a dual-channel FFT analyser, and the 2-D space-wavenumber FFT is used in some subsequent analyses.Most of the methods and experiments are further related to the two-transducer sound intensity techniques either directly or via some extension.In the method development part, the main theme is the direct measurement of acoustic impedance with the intensity technique. This is followed by additional developments for the determination of the incident power of an arbitrary sound field, the radiation efficiency, absorption coefficient and transmission loss.Two versions of the incident power method were formulated, one employs direct calculation of the Rayleigh integral the space domain, and the other uses holographic approach in the wavenumber domain.The impedance technique is also used in the 3-D acoustic modal analysis of cavities.Measurements of the flow intensity are treated as well.In addition, some current advanced techniques, including multiple input coherence analysis, spatial Fourier transform and nearfield acoustic holography are reviewed, for use in the supporting analyses of the applicability experiments with the new methods.In the experimental part, a number of simple acoustical systems are analysed using the new developed methods and, whenever possible, other wellknown methods for comparison purposes.The investigated systems include a wool absorbent, grass-covered ground surface, a loudspeaker, a two-pane window, a wind tunnel, and a simple model silencer.The main results of the experiments indicate that: (a) the direct impedance technique seems to work satisfactorily in a wide range of applications both for boundaries with incoming sound and for radiation from sources; (b) the direct determination of incident power was successful in both the tested cases, the well absorbing wool and the highly reflecting window; (c) acoustic modal analysis of simple cavities is possible using standard structural analysis software and intensity instrumentation; and (d) intensity-based methods offer a number of new applications for analysing sound propagation and attenuation in ducts.Consequently, the presented methods considerably extend the possibilities available for investigating more complicated acoustical systems such as the window.
Original languageEnglish
QualificationDoctor Degree
Awarding Institution
  • Helsinki University of Technology
Award date18 Aug 1990
Place of PublicationEspoo
Publisher
Print ISBNs951-38-3760-2
Publication statusPublished - 1990
MoE publication typeG4 Doctoral dissertation (monograph)

Fingerprint

fast Fourier transformations
wool
acoustics
impedance
silencers
sound intensity
grasses
cavities
acoustic impedance
sound propagation
transmission loss
loudspeakers
wind tunnels
absorbents
radiation
sound fields
ducts
structural analysis
holography
absorptivity

Keywords

  • acoustic measurements
  • sound waves
  • methods
  • intensity
  • impedance
  • radiation
  • absorption
  • transmission
  • modal analysis
  • holography

Cite this

Lahti, T. (1990). Analysis methods for acoustical systems based on the FFT and intensity techniques: Dissertation. Espoo: VTT Technical Research Centre of Finland.
Lahti, Tapio. / Analysis methods for acoustical systems based on the FFT and intensity techniques : Dissertation. Espoo : VTT Technical Research Centre of Finland, 1990. 291 p.
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abstract = "A two-part study on the measurement and analysis of acoustical systems is presented, consisting of the development of various new methods based on the FFT and intensity, and a collection of experiments for testing their applicability.The common factor in the studies is the FFT: the measurements were made with a dual-channel FFT analyser, and the 2-D space-wavenumber FFT is used in some subsequent analyses.Most of the methods and experiments are further related to the two-transducer sound intensity techniques either directly or via some extension.In the method development part, the main theme is the direct measurement of acoustic impedance with the intensity technique. This is followed by additional developments for the determination of the incident power of an arbitrary sound field, the radiation efficiency, absorption coefficient and transmission loss.Two versions of the incident power method were formulated, one employs direct calculation of the Rayleigh integral the space domain, and the other uses holographic approach in the wavenumber domain.The impedance technique is also used in the 3-D acoustic modal analysis of cavities.Measurements of the flow intensity are treated as well.In addition, some current advanced techniques, including multiple input coherence analysis, spatial Fourier transform and nearfield acoustic holography are reviewed, for use in the supporting analyses of the applicability experiments with the new methods.In the experimental part, a number of simple acoustical systems are analysed using the new developed methods and, whenever possible, other wellknown methods for comparison purposes.The investigated systems include a wool absorbent, grass-covered ground surface, a loudspeaker, a two-pane window, a wind tunnel, and a simple model silencer.The main results of the experiments indicate that: (a) the direct impedance technique seems to work satisfactorily in a wide range of applications both for boundaries with incoming sound and for radiation from sources; (b) the direct determination of incident power was successful in both the tested cases, the well absorbing wool and the highly reflecting window; (c) acoustic modal analysis of simple cavities is possible using standard structural analysis software and intensity instrumentation; and (d) intensity-based methods offer a number of new applications for analysing sound propagation and attenuation in ducts.Consequently, the presented methods considerably extend the possibilities available for investigating more complicated acoustical systems such as the window.",
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author = "Tapio Lahti",
year = "1990",
language = "English",
isbn = "951-38-3760-2",
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}

Lahti, T 1990, 'Analysis methods for acoustical systems based on the FFT and intensity techniques: Dissertation', Doctor Degree, Helsinki University of Technology, Espoo.

Analysis methods for acoustical systems based on the FFT and intensity techniques : Dissertation. / Lahti, Tapio.

Espoo : VTT Technical Research Centre of Finland, 1990. 291 p.

Research output: ThesisDissertationMonograph

TY - THES

T1 - Analysis methods for acoustical systems based on the FFT and intensity techniques

T2 - Dissertation

AU - Lahti, Tapio

PY - 1990

Y1 - 1990

N2 - A two-part study on the measurement and analysis of acoustical systems is presented, consisting of the development of various new methods based on the FFT and intensity, and a collection of experiments for testing their applicability.The common factor in the studies is the FFT: the measurements were made with a dual-channel FFT analyser, and the 2-D space-wavenumber FFT is used in some subsequent analyses.Most of the methods and experiments are further related to the two-transducer sound intensity techniques either directly or via some extension.In the method development part, the main theme is the direct measurement of acoustic impedance with the intensity technique. This is followed by additional developments for the determination of the incident power of an arbitrary sound field, the radiation efficiency, absorption coefficient and transmission loss.Two versions of the incident power method were formulated, one employs direct calculation of the Rayleigh integral the space domain, and the other uses holographic approach in the wavenumber domain.The impedance technique is also used in the 3-D acoustic modal analysis of cavities.Measurements of the flow intensity are treated as well.In addition, some current advanced techniques, including multiple input coherence analysis, spatial Fourier transform and nearfield acoustic holography are reviewed, for use in the supporting analyses of the applicability experiments with the new methods.In the experimental part, a number of simple acoustical systems are analysed using the new developed methods and, whenever possible, other wellknown methods for comparison purposes.The investigated systems include a wool absorbent, grass-covered ground surface, a loudspeaker, a two-pane window, a wind tunnel, and a simple model silencer.The main results of the experiments indicate that: (a) the direct impedance technique seems to work satisfactorily in a wide range of applications both for boundaries with incoming sound and for radiation from sources; (b) the direct determination of incident power was successful in both the tested cases, the well absorbing wool and the highly reflecting window; (c) acoustic modal analysis of simple cavities is possible using standard structural analysis software and intensity instrumentation; and (d) intensity-based methods offer a number of new applications for analysing sound propagation and attenuation in ducts.Consequently, the presented methods considerably extend the possibilities available for investigating more complicated acoustical systems such as the window.

AB - A two-part study on the measurement and analysis of acoustical systems is presented, consisting of the development of various new methods based on the FFT and intensity, and a collection of experiments for testing their applicability.The common factor in the studies is the FFT: the measurements were made with a dual-channel FFT analyser, and the 2-D space-wavenumber FFT is used in some subsequent analyses.Most of the methods and experiments are further related to the two-transducer sound intensity techniques either directly or via some extension.In the method development part, the main theme is the direct measurement of acoustic impedance with the intensity technique. This is followed by additional developments for the determination of the incident power of an arbitrary sound field, the radiation efficiency, absorption coefficient and transmission loss.Two versions of the incident power method were formulated, one employs direct calculation of the Rayleigh integral the space domain, and the other uses holographic approach in the wavenumber domain.The impedance technique is also used in the 3-D acoustic modal analysis of cavities.Measurements of the flow intensity are treated as well.In addition, some current advanced techniques, including multiple input coherence analysis, spatial Fourier transform and nearfield acoustic holography are reviewed, for use in the supporting analyses of the applicability experiments with the new methods.In the experimental part, a number of simple acoustical systems are analysed using the new developed methods and, whenever possible, other wellknown methods for comparison purposes.The investigated systems include a wool absorbent, grass-covered ground surface, a loudspeaker, a two-pane window, a wind tunnel, and a simple model silencer.The main results of the experiments indicate that: (a) the direct impedance technique seems to work satisfactorily in a wide range of applications both for boundaries with incoming sound and for radiation from sources; (b) the direct determination of incident power was successful in both the tested cases, the well absorbing wool and the highly reflecting window; (c) acoustic modal analysis of simple cavities is possible using standard structural analysis software and intensity instrumentation; and (d) intensity-based methods offer a number of new applications for analysing sound propagation and attenuation in ducts.Consequently, the presented methods considerably extend the possibilities available for investigating more complicated acoustical systems such as the window.

KW - acoustic measurements

KW - sound waves

KW - methods

KW - intensity

KW - impedance

KW - radiation

KW - absorption

KW - transmission

KW - modal analysis

KW - holography

M3 - Dissertation

SN - 951-38-3760-2

T3 - Publications / Technical Research Centre of Finland

PB - VTT Technical Research Centre of Finland

CY - Espoo

ER -

Lahti T. Analysis methods for acoustical systems based on the FFT and intensity techniques: Dissertation. Espoo: VTT Technical Research Centre of Finland, 1990. 291 p.