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The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. More simply, the speed of sound is how fast vibrations travel. At 20 °C (68 °F), the speed of sound in air, is about 343 m/s (1,125 ft/s; 1,235 km/h; 767 mph; 667 kn), or 1 km in 2.91 s or one mile in 4.69 s.
However, unlike the spacetime metric, in which the invariant speed is the absolute upper limit on the propagation of all causal effects, the invariant speed in an acoustic metric is not the upper limit on propagation speeds. For example, the speed of sound is less than the speed of light.
Once the speed of sound in the air was known, this allowed Kundt to calculate the speed of sound in the metal of the resonator rod. The length of the rod L was equal to a half wavelength of the sound in metal, and the distance between the piles of powder d was equal to a half wavelength of the sound in air. So the ratio of the two was equal to ...
If the distance from the transducer to the reflector is known, and the time taken from the transmit to the receive pulse is known, then the speed of sound in water can be calculated. Transducers used in sound velocity probes are typically of a high frequency (around 1 - 4 MHz) as the transmit and receive distances are close enough to mitigate ...
They measured a sound speed of 1435 metres per second over a 17 kilometre (km) distance, providing the first quantitative measurement of sound speed in water. [4] The result they obtained was within about 2% of currently accepted values. In 1877 Lord Rayleigh wrote the Theory of Sound and established modern acoustic theory.
If the sound pressure p 1 is measured at a distance r 1 from the centre of the sphere, the sound pressure p 2 at another position r 2 can be calculated: =. The inverse-proportional law for sound pressure comes from the inverse-square law for sound intensity: I ( r ) ∝ 1 r 2 . {\displaystyle I(r)\propto {\frac {1}{r^{2}}}.}
where is the Laplace operator, is the acoustic pressure (the local deviation from the ambient pressure), and is the speed of sound. A similar looking wave equation but for the vector field particle velocity is given by
The lack of reflections in a free field means that any sound in the field is entirely determined by a listener or microphone because it is received through the direct sound of the sound source. This makes the open field a direct sound field. [3] In a free field, sound is attenuated with increased distance according to the inverse-square law. [1]