Let us examine the behaviour of sound in a gas or in a liquid medium. From a physical point of view, the sound we hear is created by the pressure change in the medium surrounding us that is sensed by our ears. The equations describing the behaviour of a liquid or a gas are based on well-known equations of fluid mechanics. Therefore in acoustics, they are often referred to as fluids. In the following sections we present a simple wave equation, which is the simplest of (linear) equations used to model acoustical phenomena. Even though the wave equation is quite a simplified model, it has proven to be extremely useful for describing the behaviour of sound in the most common fluid we face every day, namely air.
KeywordsSource Term Sound Source Helmholtz Equation Dipole Source Eigenfunction Expansion
- 4.Karjalainen, M., Ikonen, V., Antsalo, P., Maijala, P., Savioja, L., Suutala, A., Pohjolainen, S.: Comparison of numerical simulation models and measured low-frequency behavior of loudspeaker enclosures. J. Audio Eng. Soc. 49 (12), 1148–1166 (2001)Google Scholar
- 5.Morse, P.M., Ingard, U.K.: Theoretical Acoustics, 2nd edn. Princeton University Press, Princeton (1986)Google Scholar
- 6.Pierce, A.D.: Acoustics, an Introduction to Its Physical Principles and Applications. Acoustical Society of America, Woodbury (1989)Google Scholar
- 7.Rankonen, T.: Akustinen materiaaliominaisuuksien mittaus ja mallinnus (Modelling and Measuring Material’s Acoustical Properties) (In Finnish). Master’s thesis, Tampere University of Technology (2002)Google Scholar
- 8.Suutala, A.: Matemaattinen mallinnus akustiikassa (Mathematical Modelling in Acoustics) (In Finnish). Master’s thesis, Tampere University of Technology (1998)Google Scholar