xviii Introduction
concerned, these are not covered in any detail except for the important area of vibration
isolation. The basis for this type of isolation is included as a part of the general
description of mechanical oscillations.
Some readers will certainly miss a chapter on the subjective aspects of sound — the
human hearing mechanism and the relationship between the objective, measurable
quantities and the subjectively adjusted measurement quantities such as the frequency
weighted sound pressure levels, using the A- or C-weighting curve, or the loudness or
loudness level expressed in sone and phon, respectively. These aspects are, however,
thoroughly treated in a number of books on noise and noise abatement allowing us to
leave it out here. This said, it should be stressed that our ears are among the best
instruments for acoustic analysis. A building acoustics “diagnosis” may often be put
forward more easily by placing your ear to the wall than using an instrument.
The understanding of the performance of simple mechanical vibrating systems is
basic for the understanding of the behaviour of complex systems such as the building
elements and constructions one finds in buildings. Chapter 1 gives an overview of how
oscillations of various types, periodic, transient as well as stochastic (random), are
characterized and analysed in the time domain as well as in the frequency domain. In
Chapter 2, the transfer of such oscillations through mechanical systems is treated, starting
from systems made up of the concentrated (lumped) elements mass, spring and damper.
This provides the base for a transition to continuous systems where wave phenomena
become dominant.
In Chapter 3, we describe wave phenomena in fluid as well as in solid media, the
sources of sound waves and their propagation in these media. Particular emphasis is
placed on the subject of bending (flexural) waves to provide the background for treating
sound transmission through building elements.
Chapter 4 is devoted to room acoustics with emphasis on the physical aspects.
However, an overview of the room acoustic parameters for characterizing the acoustic
quality with respect to transmission of music and speech is included. Important
measuring quantities, which must be determined in practice, e.g. determining sound
insulation, are also treated along with the expected measurement accuracy of these
quantities.
Chapter 5 is wholly devoted to acoustic absorbing materials and constructions,
modelling the absorption of sound in porous materials as well as the absorption offered
by absorbers based on a resonator principle, membrane absorbers and absorbers of
Helmholtz type. The last, based on microperforated panels, is given a broad treatment.
Measuring methods for absorption and for the determination of material properties,
important for modelling the absorption capability of absorbers, are thoroughly treated.
Chapter 6 introduces the measures used to characterize the sound isolating
capability of building elements and constructions; i.e. the sound reduction index (also
known as transmission loss) and impact sound pressure level, along with their frequency
weighted counterparts. The treatment of sound transmission phenomena starts with a
look at the ability of the elements to act as sound radiators, thereafter how these elements
are vibrating when forced, either by point or distributed forces (pressure field). The
treatment in this chapter is limited to single leaf partitions.
Statistical energy analysis (SEA) is a method for prediction of the dynamic
behaviour of complex systems, containing both acoustic and structural elements. The
method has gained wide acceptance for use in building acoustics and a short introduction
is therefore given in Chapter 7, partly to give some background to the results presented in
the remaining chapters.
Chapter 8 extends the treatment on sound transmission to composite elements such
as double leaf constructions, sandwich elements etc. and the last chapter, Chapter 9,