Sound

Sound (of old-high-German scal) that generally designates Noise, that Sound, that Clay/tone, as it by humans and also of animals to be heard can. Sound places those Propagation of smallest pressure and density disturbances in a flexible medium (gases, liquids, solids). One differentiates between that Utilizable sound, like music or the voice with the discussion, and that Wind noise, like building site or traffic noise.

Table of contents

Definition

sound one is seen . In gases and in liquids sound is always one Longitudinal wave, thus also in the most important medium, in air. In solids it gives also Transverse waves. Acoustic waves transport Oscillations and . They move (mostly air) around middle being entitled and spread with a characteristic does not existent.

The associated science is those and locally periodic changes physical dimension are temporal g(t, x). That Sound pressure p the most important sound field size is as Scalarly at all (see also Pressure wave). This has different reasons: The sound pressure is a descriptive size, detectable with microphones relatively easily measurably and also by humans physiologically. The sound field size Acoustic velocity v is in Vector, whereby during effect of sound the "speed" of moving back and forth of the fluid elements (air particles) is meant. The term "speed" becomes here the clear demarcation Speed of sound C however avoided. The fast one is not so easily assignable. One must realize here that the maximally arising speeds with that Deflection the fluid elements in the comparison to the speed of sound are small: With a sound pressure of 120 railways the fast one amounts toamplitude in air straight once 0.05 m/s. With that Auditory threshold humans of 0 railways the fast amplitude has a value of 5 · 10-8 m/s. Here the air particles are only completely small expenditure-steered.

Organization according to frequency

According to that one differentiates:

  • < 16 cycles per second are not audibly, there too low frequent for humans
  • Hoerschall from 16 cycles per second to 20 kHz, audible sound is for humans
  • Ultrasonic from 20 kHz to 10 GHz is not audibly, there too high frequency for humans
  • Hypersonic > 10 GHz are only cause propagationable waves

Reduction of wind noise

During the noise fight between directly produced and indirectly produced airborne sound one differentiates. Directly produced airborne sound develops without the participation of impact sound (z.B. in a jet engine). With the indirectly produced airborne sound by a suggestion for force first impact sound in a structure is produced. This reproduces itself in the structure. Airborne sound is then radiated by vibrations at the surface of the structure.

With the directly produced airborne sound the turbulence of air must be kept small for noise sinking. Particularly it is to be made certain that construction units are not subjected to swirled current (s. Aero acoustics). With the indirectly produced airborne sound can be set at different points. First the force relationship can be affected in such a way that it energizes if possible few natural frequencies of the construction unit. This is the case whenever no steep force jumps or force points are present. Further those can Feed impedance the construction unit to be increased (z.B. by increased mass in the force application place. Finally the structure can be dampened (z.B. by Entdroehnung with heavy mats or Sand yielding sheet metals).

Examples of the application of primary and secondary mechanisms are:

  • Noise protection wall
  • traffic-calmed down ranges
  • Speed limitings
  • Protection of the ears ("ear plugs")
  • Sound-insulating window
  • Sound compensation
  • exhaustless Design of
  • Spindleloose Design of (thus without classical
     

      > German to English > de.wikipedia.org (Machine translated into English)