The importance of sound
Sound is a ubiquitous component of our environment from which there is no escape.
Even in the darkness of a deep underground cavern, the potholer hears the sound of the
operation of his or her body. In the dark depths of the ocean, creatures communicate by
sound, which is the only form of wave that propagates over long distances in water. Only
in the reaches of cosmic space, and in high vacuums created on Earth, are atoms so
isolated that the chance of interaction, and hence the existence of sound, is negligible.
Sound is one of the principal media of communication between human beings,
between higher animals, and between humans and domesticated animals. Sound
informs us about our environment; as a result of evolution we find some sounds
pleasant and some redolent of danger. The universal importance of music to human
beings, and its emotional impact, remain mysterious phenomena that have yet to be
satisfactorily explained. Unlike our eyes, our ears are sensitive to sound arriving from
all directions; as such they constitute the sensors of our principal warning system,
which is alert even when we are asleep.
So, sound is vitally important to us as human beings. But, apart from audio
engineers who capture and reproduce sound for a living, why should engineers
practising in other fields have any professional interest in sound? The short answer
has two parts. On the positive side, sound can be exploited for many purposes of
concern to the engineer, as indicated later in this chapter. On the negative side,
excessive sound has adverse psychological and physiological effects on human beings
that engineers are employed to mitigate, preferably by helping to design inherently
quiet machines, equipment and systems: but failing this, by developing and applying
noise control measures.
The adverse effects of excessive sound in causing hearing damage, raising stress
levels, disturbing rest and sleep, reducing the efficiency of task performance, and
interfering with verbal and musical communication, are widely experienced, recognized
and recorded. In recent years, noise has become a major factor in influencing the
marketability and competitiveness of industrial products such as cars and washing
machines, as evidenced by advertising material. Many products are required to satisfy
legal and regulatory requirements that limit the emission of noise into work places,
homes and the general environment. Failure to meet these requirements has very
serious commercial consequences. Aircraft are not certificated for commercial operation
unless they meet very stringent environmental noise limits. Road vehicles are not
allowed on the road unless they satisfy legally enforced limits on roadside noise. Train
noise is currently being subjected to the imposition of noise restrictions.
A less widely known adverse effect of excessive sound is its capacity to inflict serious
fatigue damage on mechanical systems, such as the structures of aircraft, space rockets
and gas pipelines, and to cause malfunction of sensitive components, such as the
electronic circuits of Earth satellites. Sound is vitally important to the military,
particularly with the advent of automated target recognition and ranging systems.
Sound is a tell-tale. It gives warning that mechanical and physiological systems are
not in good health. Sound generated by the pulmonary and cardiovascular systems
provides evidence of abnormal state or operation, as foreseen by Robert Hooke over
300 years ago. The production of equipment for monitoring the state of machinery via
acoustic and vibrational signals is a multimillion dollar business. The cost of
monitoring is small compared with the cost of one day's outage of a 600 MW
turbogenerator, which runs into more than one million dollars.
Taken together, these different aspects of the impact of sound on human beings and
engineering products provide convincing reasons why acoustics is a fascinating subject
of study and practice for engineers.
Even in the darkness of a deep underground cavern, the potholer hears the sound of the
operation of his or her body. In the dark depths of the ocean, creatures communicate by
sound, which is the only form of wave that propagates over long distances in water. Only
in the reaches of cosmic space, and in high vacuums created on Earth, are atoms so
isolated that the chance of interaction, and hence the existence of sound, is negligible.
Sound is one of the principal media of communication between human beings,
between higher animals, and between humans and domesticated animals. Sound
informs us about our environment; as a result of evolution we find some sounds
pleasant and some redolent of danger. The universal importance of music to human
beings, and its emotional impact, remain mysterious phenomena that have yet to be
satisfactorily explained. Unlike our eyes, our ears are sensitive to sound arriving from
all directions; as such they constitute the sensors of our principal warning system,
which is alert even when we are asleep.
So, sound is vitally important to us as human beings. But, apart from audio
engineers who capture and reproduce sound for a living, why should engineers
practising in other fields have any professional interest in sound? The short answer
has two parts. On the positive side, sound can be exploited for many purposes of
concern to the engineer, as indicated later in this chapter. On the negative side,
excessive sound has adverse psychological and physiological effects on human beings
that engineers are employed to mitigate, preferably by helping to design inherently
quiet machines, equipment and systems: but failing this, by developing and applying
noise control measures.
The adverse effects of excessive sound in causing hearing damage, raising stress
levels, disturbing rest and sleep, reducing the efficiency of task performance, and
interfering with verbal and musical communication, are widely experienced, recognized
and recorded. In recent years, noise has become a major factor in influencing the
marketability and competitiveness of industrial products such as cars and washing
machines, as evidenced by advertising material. Many products are required to satisfy
legal and regulatory requirements that limit the emission of noise into work places,
homes and the general environment. Failure to meet these requirements has very
serious commercial consequences. Aircraft are not certificated for commercial operation
unless they meet very stringent environmental noise limits. Road vehicles are not
allowed on the road unless they satisfy legally enforced limits on roadside noise. Train
noise is currently being subjected to the imposition of noise restrictions.
A less widely known adverse effect of excessive sound is its capacity to inflict serious
fatigue damage on mechanical systems, such as the structures of aircraft, space rockets
and gas pipelines, and to cause malfunction of sensitive components, such as the
electronic circuits of Earth satellites. Sound is vitally important to the military,
particularly with the advent of automated target recognition and ranging systems.
Sound is a tell-tale. It gives warning that mechanical and physiological systems are
not in good health. Sound generated by the pulmonary and cardiovascular systems
provides evidence of abnormal state or operation, as foreseen by Robert Hooke over
300 years ago. The production of equipment for monitoring the state of machinery via
acoustic and vibrational signals is a multimillion dollar business. The cost of
monitoring is small compared with the cost of one day's outage of a 600 MW
turbogenerator, which runs into more than one million dollars.
Taken together, these different aspects of the impact of sound on human beings and
engineering products provide convincing reasons why acoustics is a fascinating subject
of study and practice for engineers.
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