Structure-borne sound sources in buildings

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Lievens, Matthias; Vorländer, Michael (Thesis advisor)

Berlin : Logos-Verl. (2013)
Dissertation / PhD Thesis

In: Aachener Beiträge zur technischen Akustik 15
Page(s)/Article-Nr.: V, 99 S. : Ill., graph. Darst.

Zugl.: Aachen, Techn. Hochsch., Diss., 2013

Abstract

Structure-borne sound sources are vibrational sources connected in some way to the building structure. The mechanical excitation of the building structure leads to sound radiation. This is an important source of annoyance in modern light-weight buildings. The prediction of the sound pressure level from structure-borne sound sources is highly complicated because of the complexity involved in the coupling between source and receiver structure. The current standard on characterisation of service equipment in buildings EN 12354-5, can deal with sources on heavy structures (high-mobility source) but to date, there is no engineering method available for the case of coupling between source and receiver. To develop a practical engineering method it is crucial to determine the important degrees of freedom. The coupling between source and receiver can theoretically be described by a mobility approach through six degrees of freedom at every contact point. This leads to an enormous amount of data that has to be simplified. One of the assumption frequently made in the field of building acoustics is to use the normal components only. This aspect is investigated in this thesis on a case study of a washing machine on a wooden joist floor. The directly measured sound pressure level is compared with the predicted sound pressure level. The prediction is based on normal components only. Moment excitation is minimised by reducing the contact area between source and receiver while the in-plane components are assumed negligible. In the first part of this thesis, measurements in the coupled state are conducted. It is shown that the normal components are sufficient to predict the sound pressure level. However, this only applies to the coupled state. In the second part, a true prediction is calculated from independently measured source and receiver quantities. The difference between predicted and directly measured sound pressure level leads to considerable errors of up to 20 dB at low frequencies. This shows that the normal components are not sufficient to predict the coupling between a washing machine and a wooden floor.