FUNDAMENTALS OF ACOUSTICS FINN JACOBSE

FUNDAMENTALS OF ACOUSTICS
AND NOISE CONTROL
Finn Jacobsen, Torben Poulsen, Jens Holger Rindel,
Anders Christian Gade and Mogens Ohlrich

Department of Electrical Engineering, Technical University of Denmark
September 2011
Note no 31200

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CONTENTS
Page
1

An elementary introduction to acoustics ....................................................................1
Finn Jacobsen

1.1

Introduction ....................................................................................................................1

1.2

Fundamental acoustic concepts ......................................................................................1
1.2.1 Plane sound waves .............................................................................................4
1.2.2 Spherical sound waves .....................................................................................13

1.3

Acoustic measurements ................................................................................................15
1.3.1 Frequency analysis ...........................................................................................15
1.3.2 Levels and decibels .........................................................................................18
1.3.3 Noise measurement techniques and instrumentation .......................................21

1.4

The concept of impedance............................................................................................27

1.5

Sound energy, sound intensity, sound power and sound absorption ............................31
1.5.1 The energy in a sound field ..............................................................................32
1.5.2 Sound absorption ..............................................................................................35

1.6

Radiation of sound .......................................................................................................37
1.6.1 Point sources

References: London, 1994.