Sound

  • Sound pressure
  • SPL
  • Sound velocity
  • Schallauslenkung
  • Sound acceleration
  • Sound intensity
  • Sound power
  • Sound energy density
  • Sound energy
  • Sonic flow
  • Acoustic impedance
  • Speed of sound

Sound (from Old High German: scal ) generally the sound, the sound, the sound, the bang (sound modes), as it can be perceived auditory of people with hearing, that the ear - brain system, but also of animals. Sound is the smallest spread of pressure and density fluctuations in an elastic medium (gases, liquids, solids) dar. We distinguish the desired sounds, such as music or voice during a conversation, and the background noise, such as construction sites or traffic noise.

Physical definition

Physically, sound is a progressive wave as mechanical deformation in a medium. In resting gases and liquids sound is always a longitudinal wave, ie approximately in air. The general wave equation for three-dimensional sound fields in fluid media is:

Sound spreads out with one for the medium and its state ( temperature, pressure, etc. ) characteristic and constant speed of sound. At a temperature of 20 ° C in air, these 343 m / s in water and 1484 m / sec, see also the speed of sound in different media. The wavelength of the sound wave can be calculated at a given frequency and sound velocity by the relation:

In gases, such as air-borne sound can be used as a static air pressure superimposed sound pressure wave are described. Most of the fluctuations of the state variables of pressure and density are sound waves at small relative to their resting size. This is vividly when sound pressure level of 130 dB ( decibels), which is about the pain threshold of people, compared with the normal atmospheric pressure: The static pressure of the atmosphere is 101325 Pascals ( = 1013.25 hPa ), while a sound pressure level of 130 dB an effective value of the sound pressure p of just 63 Pascal equals.

On the other hand, there are also transverse waves in solids and guided waves. In a vacuum, there is no sound, as it always does, in contrast to electromagnetic waves, a carrier medium.

Acoustics

The relevant science is the acoustics, which in turn is a sub- field of gas dynamics. The two forms of energy are converted into each other with the sound, the compression energy and the kinetic energy as sound energy quantity, but they are characterized by the sound field quantities:

  • Sound pressure p in N/m2 = Pa ( Pascal )
  • Sound velocity v in m / s

Waves are temporally and spatially periodic variations of a physical quantity g ( t, x). The sound pressure p is the most important sound field quantity as a scalar at all; see also pressure wave. This has several reasons: The sound pressure is a descriptive measurement, relatively easy to measure with microphones and physiologically detectable even by humans. The sound pressure p is easy to measure. With a sound pressure level of 0 dB, ie, at the threshold of hearing, has the sound pressure as RMS value, a value of 2 x 10-5 N/m2 ( Pascal ). However, the size of the sound field sound velocity v is a vector, under the influence of sound, the speed of the reciprocating motion of the fluid elements ( air particles ) is meant. The term speed is, however, avoided here for the clear demarcation between the speed of sound c. The Fast is not so easily determined. It must be, be aware that the speeds maximum occurring are small during the deflection of the fluid elements in comparison to the speed of sound: With a sound pressure level of 130 dB, the threshold of pain, the sound velocity is in the air just 0.153 m / s At the threshold of human hearing, the rms value of the sound velocity has a value of 5 x 10-8 m / s corresponding to a particle velocity level of 0 dB. Here, the air particles are deflected only very small.

Classification by frequency

According to the frequency range it may be:

  • Infrasound <16 Hz is not audible to humans, because the frequency is too low
  • Audible sound from 16 Hz to 20 kHz, is for people audible sound
  • Ultrasound of 20 kHz to 1.6 GHz is not audible to humans, since at high frequency
  • Hypersonic > 1 GHz is formed by sound waves, which are only partly capable of propagation

View the types of sound

The following schematic oscilloscope images illustrate the different types of sound:

Sound: periodically (eg violin sound )

Sound: periodic, sinusoidal ( eg tuning fork )

Bang: initially high amplitude (eg gunshot )

Musical tone Transmission medium
39068
de