The influence of finite and infinite wall cavities on the sound insulation of double-leaf walls.
Theories used to predict the sound insulation of double-leaf cavity wall systems are usually based on the assumption that the wall is of an infinite extent. To account for the effect of the finite extent of the wall, limiting the angle of incidence, a finite radiation efficiency model or the spatial windowing method is used in order to obtain realistic predictions. However, the effects of the finite extent of the cavity are often not included. This paper presents an extension of a finite two-dimensional cavity theory to include limp panels on each side of the cavity. It is shown that the oblique incidence mass-air-mass resonance can only occur for certain frequencies and certain angles of incidence. This is the reason why the infinite extent theories under-predict the sound insulation. The results of the predicted sound insulation agree with measurements when the wall cavity is empty. To obtain agreement when the cavity is full of a porous sound absorbing material, a flow resistivity of about one-fifth of the measured value has to be used. Use of the actual flow resistivity gives sound insulation values that are 10 dB too high.
Department of Mechanical Engineering, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand.
Jason E
JE
Cambridge
School of Science, Royal Melbourne Institute of Technology (RMIT) University, GPO Box 2476 Melbourne, Victoria 3001, Australia.
John L
JL
Davy
Department of Mechanical Engineering, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand.
John
J
Pearse