Sound pressure

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

The sound pressure or sound pressure, the formula p ( engl. "pressure " - pressure), is the most important sound field quantity in audio engineering and acoustics.

Definition

As sound pressure, the sound pressure variations of a compressible transfer medium ( usually air ) be referred to, which occur during the propagation of sound. These pressure fluctuations are converted from the tympanic membrane as a sensor in movements to auditory perception. If it is an audible sound, such movements can then be carried out by the inner ear ( ear -brain system).

The sound pressure P is the pressure change ( a size ) of P0 ( atmospheric pressure) is superimposed on the static pressure of the surrounding medium. This is the sound pressure

With the force acting on the area A force F per area of A.

Thus applies for the entire pressure pges:

The sound pressure p ( sound pressure ) is generally many orders of magnitude smaller than the static pressure. As a print with no indication of direction can be linked, it is a scalar quantity. The sound pressure as a function of the coordinates in three-dimensional space from a mathematical point of view thus a scalar field.

The SI unit of sound pressure, as the pressure is the Pascal with the unit symbol Pa. The sound pressure is expressed as a level often size (see sound pressure level ) in dB.

Furthermore, in sinusoidal signals is the indication as an effective value

Usual. The sound pressure amplitude, however, is the peak value (peak value) of the sound pressure.

Is it the sound of a tone, ie a harmonic oscillation (often called " sine wave ") having only one frequency, then for the time dependence of the sound pressure:

The sound pressure amplitude and ω is the angular frequency.

Distance dependence

The rms value of the sound pressure is inversely proportional to the free-field distance r from a ( point-like ) sound source ( 1/r-Gesetz, distance law ):

= Sound pressure at a smaller distance   = Sound pressure at a greater distance

(Note: The square acoustic energy quantities, such as the sound intensity take at point sound sources with 1/r2 versus distance from. ) As you can see here, is to assess the strength of a sound source in addition to the indication of the measured sound pressure necessarily require the position of the measuring point as distance R from the sound source is necessary.

In reverberant environment, the 1/r-Gesetz applies only restricted:

  • In the direct field of the sound source, ie in the open and where the direct sound D outweighs the room sound R, the 1/r-Gesetz applies.
  • Outside of the immediate direct field where the reflections get an influence on the overall sound pressure that 1/r-Gesetz applies only limited.
  • Outside the Hall radius rH, which is the distance from the sound source at which the direct sound D is just as strong as the room sound R, the sound pressure with increasing distance from the sound source essentially because he above all of the reflections of the walls remains constant, is determined.

Conjunction with other acoustic quantities

In a plane wave of sound pressure with the acoustic quantities characteristic acoustic impedance, sound pressure, particle velocity, and sound intensity is linked as follows:

Where:

Table: Sound pressure and sound pressure level of various sound sources

Sound pressure in air (compared to static air pressure at sea level: 101 325 Pa):

Sound pressure in water:

Musical tone Metre per second Density of air Rifle
122348
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