Sound Waves transfer sound energy by vibrating the particles of the various media the sound waves pass through. The media will absorb, reflect or impede the sound energy flow in accordance with the acoustic properties of the media and the wavelength of the sound wave. In air there is little resistance (acoustic impedance) to the sound propagation, in a vacuum i.e. no media the sound cannot propagate
Sound Waves Definition (IEC 801-23-01) disturbance propagated at a definite velocity in a medium in such a manner that at any point in the medium the quantity serving as the measure of disturbance is a function of the time, while at any instant the same quantity at a point is a function of the co-ordinates of the point.
Sound Waves in air are longitudinal waves.
You can simulate sound waves while holding a length of rope and moving your hand(s) up and down or side-to-side, demonstrating the two main directions in which sound wave motion occurs, longitudinal and transverse. In both cases the rope particles are involved but without any net particle movement. Observe also the nodes and antinodes, found in all waves as they move along the rope. In the special case of standing waves these node(s) would be stationary.
Sound Waves related terms - listed alphabetically
Antinode Definition (IEC 801-23-17) point, line or surface in a standing wave where some specified characteristic of the wave field has maximum amplitude.
Note : the appropriate modifier should be used before the word antinode to signify the type that is intended; e.g. displacement antinode, particle velocity antinode, sound pressure antinode.
Compressional Wave Definition (IEC 801-23-04) wave in an elastic medium that causes an element of the medium to change its volume without undergoing rotation
Note : mathematically, a compressional wave is one whose velocity field has zero curl.
Cylindrical Wave Definition (IEC 801-23-08) wave of which the wave fronts are coaxial cylinders.
Similarly when sound waves pass through a gap they spread out depending on the gap size and the wavelength (frequency).
Diffraction Factor Definition (IEC 801-25-55) for a specified frequency and specified direction of incident sound, it is the ratio of the sound pressure acting on the part of a transducer designed to receive sound, to the free-field sound pressure at that place in the absence of the transducer.
Dispersion Definition (IEC 801-23-22) separation of the sinusoidal components of a wave that results from change of speed of sound with frequency.
Free Progressive Wave
Grazing Incidence Definition (IEC 705-04-05) the incidence of a wave on a surface at a very small grazing angle.
Interference Definition (IEC 801-23-13) phenomenon that results from the superposition of two or more waves of the same frequency but different in phase or direction of propagation.
Longitudinal Sound Wave in which the particle displacement is in the direction the wave is travelling. The media particles do not move along the wave, they transfer energy to the next particle along the path, then return to their equilibrium point. Sound Waves in air are longitudinal waves.
Node Definition (IEC 801-23-16) a point, line or surface in a standing wave where some specified characteristic of the wave field has essentially zero amplitude
Note 1 : in practice, this amplitude is generally not zero but simply a minimum. The node is then said to be partial.
Note 2 : the appropriate modifier should be used before the word "node" to signify the type that is intended; e.g. displacement node, particle velocity node, sound pressure node.
Rayleigh Wave Definition (IEC 801-23-12) surface wave associated with the free boundary of a solid or liquid such that a surface particle describes an ellipse whose major axis is normal to the surface, and whose centre is situated on the initially undisturbed surface
Note 1 : a maximum particle displacement away from this initially undisturbed surface the motion of the particle is opposite to that of the wave.
Note 2 : the propagation velocity of a Rayleigh wave is slightly less than that of a shear wave in the solid. The wave amplitude of the Rayleigh wave diminishes exponentially with depth.
The reflected wave may interfere with the incident sound wave and cancellation or amplification may occur across the spectrum.
Rotational Wave Definition (IEC 801-23-10) wave propagating in an elastic medium that causes an element of the medium to change its shape without a change of volume, also known as a shear wave.
Note : mathematically, the particle velocity of a rotational wave has zero divergence
SAW (surface acoustic waves) under rayleigh waves
Shear Wave Definition (IEC 801-23-10) wave propagating in an elastic medium that causes an element of the medium to change its shape without a change of volume, also known as a rotational wave.
Note : mathematically, the particle velocity of a shear wave has zero divergence.
Sound Wave Propagation under sound propagation
Sound Wave Velocity Definition (IEC 801-23-19) vector that specifies the speed and direction with which a sound wave travels
When sound waves are 180 degrees out of phase and have the same amplitude, they cancel each other out.
Standing Wave Definition (IEC 801-23-15) periodic wave having a fixed distribution in space that is the result of interference of progressive waves of the same frequency and kind.
Note : such waves are characterised by the existence of nodes or partial nodes and anti-nodes that are fixed in space.
Standing Wave Tube method for measuring absorption coefficients by means of standing waves in a tube.
Superposition of Waves occur whenever two (or more) waves are travelling through the same medium at the same time, the waves combine. The net displacement of the medium at any point in space or time, is the sum of the individual wave displacements.
Surface Acoustic Wave (SAW) under rayleigh wave
Surface Wavefront Definition (IEC 801-23-02) locus of points of a progressive surface where the phase of a quantity characterising the wave is the same at a given instant.
Wavelength Definition (IEC 103-10-10) distance, in the direction of propagation of a sinusoidal wave, between two successive points where the phases of the characteristic quantity differ by 2π radians.
It can be envisaged as the number of waves that exist over a specified distance (analogous to frequency being the number of cycles or radian per unit time).