BUILDING UTILITIES 3
ACOUSTICS AND LIGHTING SYSTEMS
1.1 DEFINITION
ACOUSTICS
ACOUSTICS
• Acoustics is a science which deals with the
production, control, transmission, reception and
effects of sound in an enclosed space.
• The science of sound, including the generation,
transmission, and effects of sound waves.
ACOUSTICS
1.1 DEFINITION
SOUND
• Sound is the human ear’s response to
pressure fluctuations in the air caused by
vibrating objects; is a vibration at various
frequencies in any elastic medium.
• Generated by a source
• Requires path of transmission (gaseous, liquid,
solid)
ACOUSTICS
1.1 DEFINITION
SOUND
• For example, a tap on the wall produces sound
because the tap makes a wall vibrate. The
vibrating wall produces pressure fluctuations in
the air.
• Sound travels in space by a phenomenon
called wave motion. Wave motion in air is like
the motion of a ripple produced by dropping a
pebble into a water pond.
ACOUSTICS
1.1 DEFINITION
BASIC SOUND THEORY
Sound is an aural sensation caused by
oscillation or vibration in an elastic medium
such as air, water, building materials, such
medium returns to its normal state after
sound waves pass through it. Sound travels
in any medium except in a vacuum because
there is no carrier of sound.
ACOUSTICS
1.1 DEFINITION
SOUND GENERATION
Any change of stress or pressure producing a
local change in density or a local displacement
from equilibrium in an elastic medium can serve
as a source of sound. Other illustrations are
provided by struck solids such as a drum, violin,
or piano string, flow of air in a jet and underwater
explosion.
ACOUSTICS
1.1 DEFINITION
VIBRATION OF PARTICLE IN AIR
A full circuit by displaced particle is
called a cycle.
The time required for one complete
cycle is called the period
And the number of complete cycles per
second is the frequency of vibration.
Frequency is measured in cycles per
second, the unit for which is called the
hertz (hz).
ACOUSTICS
1.1 DEFINITION
SOUND TRANSMISSION
• Transmission of sound takes place through an
elastic medium by means of wave motion. A wave is
the motion through the medium of a disturbance as
distinguished from the motion of the medium as a
whole.
• For example, when you flick the rim of a glass, the
glass will vibrate imperceptibly. These vibrations
move through the air and strike the ear drum of
anyone within hearing range. In fact, these
vibrations, or sound waves, can move through any
medium: gas, liquid or solid.
• Sound needs a material medium for their
propagation like solid, liquid or gas to travel because
the molecules of solid, liquid and gases carry sound
waves from one point to another. Sound cannot
progress through the vacuum because the vacuum
has no molecules which can vibrate and carry the
sound waves.
ACOUSTICS
1.1 DEFINITION
SOUND TRANSMISSION
• Velocity of sound in still air of
normal atmospheric composition
at 0°C is 331.45m/s.
• Another important property of
sound transmission is intensity,
measured by the average rate of
flow of energy in the wave per
unit of time and per unit area
perpendicular to the direction of
propagation.
• The intensity of all practical
sound waves diminishes with
distance from the source, a
property known as attenuation.
ACOUSTICS
ACOUSTICS
1.1 DEFINITION
SOUND DETECTION AND EFFECT
• The detection of sound is made possible by the
incidence of transmitted sound energy or an
appropriate acoustic transducer. For human
beings with so called normal hearing, the most
important transducer is the ear, a remarkably
sensitive organ able to top detect a sound
intensity as low as 10˄-16 w/cm².
• For modern applied acoustics, transducers such
as microphone, based on piezoelectric effect, are
widely used.
• Generally speaking, any transducer used as a
source of sound is also available as a detector,
though the sensitivity varies considerably with the
type.
ACOUSTICS
1.1 DEFINITION
LONGITUDUNAL AND
TRANSVERSE WAVES
• In wave motion in a material
medium, particles of the
medium vibrate about their
positions of equilibrium. The
wave energy is carried
forward, but not the medium.
ACOUSTICS
1.1 DEFINITION
LONGITUDUNAL WAVES
One in which the vibration of the
medium is (forward and
backward) parallel to the direction
of propagation of the wave.
TRANSVERSE WAVES
One in which the vibration of
particles of the medium are
perpendicular to the direction of
motion of the wave energy.
ACOUSTICS
1.1 DEFINITION
PURE TONE
A pure tone is vibration at a single
frequency.
For example, A tuning fork, is a forkshaped acoustic resonator used in
many applications to produce a fixed
tone. The main reason for using the
fork shape is that, unlike many other
types of resonators, it produces a
very pure tone, with most of the
vibrational energy at the fundamental
frequency.
RESEARCH WORK No. 1
List down all Acoustical terminologies in a Short size bondpaper
add definitions
and Illustrations if applicable.
Deadline: Next week
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