Audio Engineering

Loudspeakers

Ian Sinclair

The conversion from electronic signals to sound is the formidable task of the loudspeaker.
In this chapter, Ian Sinclair examines principles and practice of modern loudspeaker
design.

A loudspeaker is a device that is actuated by electrical signal energy and radiates acoustic
energy into a room or open air. The selection and installation of a speaker, as well as
its design, should be guided by the problem of coupling an electrical signal source
as effi ciently as possible to an acoustical load. This involves the determination of the
acoustical load or radiation impedances and selection of a diaphragm, motor, and means
for coupling the loaded loudspeaker to an electrical signal source. The performance of
the speaker is intimately connected with the nature of its acoustic load and should not be
considered apart from it.

23.1 Radiation of Sound................................................................................................

Sound travels through the air with a constant velocity depending on the density of the
air; this is determined by its temperature and the static air pressure. At a normal room
temperature of 22°C and static pressurepo of 751 mm Hg (10^5 N/m^2 ), the density of the
ambient air is 1.18 Kg/m^3. Under these conditions, the velocity of sound is 344.8 m/s,
but 340 m/s is a practical value. The wavelength of a sound ( X ) is equal to the velocity of
propagation described by its frequency:

λ

340 m/s

.

f

(23.1)

CHAPTER 23