Chapter 5 Flashcards
Sound is
a vibration that typically propagates as an audible wave of pressure, through a transmission medium such as a gas, liquid or solid.
Acoustics
the study of mechanical waves in gases, liquids and solids including vibration, sound, ultrasound, and infrasound
the sound waves are generates by
a sound source, such as the vibrating diaphram of a stereo-speaker.
The sound source creates
vibrations in the surrounding medium
as the source continues to vibrate the medium the vibrations
propagate away from the source at the speed of sound, thus forming the sound wave
at a fixed distance from the source ……………. vary in time
the pressure, velocity and displacement of the medium
at an instant in time the
pressure, velocity and displacement vary in space
note that the particles of the medium ……………. with the sound wave
do not travel
the …………….. of the particles over time does not change
average
during propagation waves can be ……………………. by the medium
reflected
refracted
attenuated
A relationship between the density and pressure of the medium. This relationship, affected by
temperature, determines the speed of sound within the medium
Sound travels most slowly in
gases; it travels faster in liquids; and faster still in solids.
Motion of the medium itself. If the medium is moving, this movement may
increase or decrease the absolute speed of the sound wave depending on the direction of the movement.
Motion of the medium itself. If the medium is moving, this movement may increase or decrease the absolute speed of the sound wave depending on the direction of the movement. For example, sound moving through wind will have
its speed of propagation increased by the speed of the wind if the sound and wind are moving in the same direction.
If the sound and wind are moving in opposite directions, the speed of the sound wave
will be decreased by the speed of the wind.
The viscosity of the medium. Medium viscosity determines
rate at which sound is attenuated.
The viscosity of the medium. Medium viscosity determines the rate at which sound is attenuated. For many media, such as
air or water, attenuation due to viscosity is negligible.
refracted
When sound is moving through a medium that does not have constant physical properties, it may be refracted (either dispersed or focused).
Sound cannot travel through
a vacuum.
Sound is transmitted through
gases, plasma, and liquids as longitudinal waves, also called compression waves.
Through solids, however, it can be transmitted as both
longitudinal waves and transverse waves.
The energy carried by an oscillating sound wave converts
back and forth between the potential energy and the kinetic energy.
Although there are many complexities relating to the transmission of sounds, at the point of reception (i.e. the ears), sound is readily dividable into two simple elements:
pressure and time
sound is readily dividable into two simple elements: pressure and time. These fundamental elements form the basis of
all sound waves. They can be used to describe every sound we hear.
However, in order to understand the sound more fully, a complex wave is usually separated into its component parts
which are a combination of various sound wave frequencies.
Sound waves are often simplified to
a description in terms of sinusoidal plane waves.
Sound that is perceptible by humans has frequencies from about
20 Hz to 20,000 Hz
In air at standard temperature and pressure, the corresponding wavelengths of sound waves range from
17 m to 17 mm
Sometimes speed and direction are combined as
a velocity vector; wavenumber and direction are combined as a wave vector.
The speed of sound depends on
medium the waves pass through
In fresh water, also at 20 °C, the speed of sound is approximately
1,482 m/s
In steel, the speed of sound is about
5,960 m/s
The speed of sound depends on
ambient conditions
For example, the speed of sound in gases depends on
temperature
In 20 °C air at sea level, the speed of sound is approximately
343 m/s using the formula “v = (331 + 0.6 T) m/s”.
Note that the effect of the mean flow is
additive
Note that the effect of the mean flow is additive. This is a property of
linear waves
For linear waves, the phase speed with mean flow is just
the phase speed without the mean flow plus the mean flow itself.
