Sound proof construction ! Characteristics - Ishwaranand

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Sound proof construction ! Characteristics

Sound Proof construction

Sound absorbents

  • Some material having hard, rigid including non-porous surface, provide the least absorption, whereas these which are flexible, soil porous also can vibrate, absorb more extra sound
  • The efficiency about the sound absorption depends and upon the porosity of every material used essentially sound absorbent
  • The term used to express the percentage of the incident sound that can be absorbed by a material is known as the absorption coefficient of the material
  • If the absorption coefficient of a material is 0.75, mean that the material is capable of absorbing 75 % of the incident sound
  • Each absorption coefficient changes with the frequency of every incident sound
  • low-density materials have higher absorption co-efficient 
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Classification of  Absorbents

  1. Porous absorbents
  2. Resonant absorbents
  3. Cavity resonators
  4. Composite type of absorbents

Porous absorbents

  • When sound waves strike that surface from a porous material, a part of the waves make reflected while a component enters the pores of the material including dissipated within heat energy
  • These efficiencies of this sort of absorbent increases with the increase in the resistance granted by the material
  • It is used to absorb sound having a high frequency
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Resonant absorbents

  • Some absorbent material is fixed toward sound framing timber with an air space between each framing including the wall near back.
  • Such an arrangement runs most efficient during absorbing sound waves at a base frequency
  • This principle of sound absorption is that sound waves of the appropriate frequency cause sympathetic vibrations in the panel which serves to be a diaphragm
  • Some absorption of sound uses place under the dampening of some sympathetic vibration.
  • The dampening effect of this system can be improved by placing a porous material in the air space.

Cavity resonators

  • It essentially consists of a chamber with a narrow opening (entrance) in which absorption takes place by the resonance of the air in the chamber which gives loss of sound energy
  • Such an arrangement container work effectively over a single picked frequency.
  • Application of cavity resonator is usually restricted to absorption from an individual machine or in similar cases
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Composite type of absorbents

  • They consist of perforated panels mounted on battens to leave a cavity between panels and wall at the back
  • The panels may be of metal, wood (plywood) hard broad, plasterboard, etc
  • The range of holes in the panel should differ between 10 to 20 % of each total area of the panel.
  • When some sound strikes the panel, the sound waves pass through the holes also get damped through the resonance of the air in that cavity.
  • That effectiveness of that system can be increased by placing a porous material same mineral wood etc. in this cavity
  • This type of absorbent is commonly used, as it is easy to install, economical and it can accommodate a wide range of frequencies

Characteristics of audible sound

There are three characteristics of sound 

  1. Intensity & loudness
  2. Frequency & pitch

Intensity & loudness

  • The intensity of sound is defined as the amount of flow of wave energy crossing per unit time through a unit area taken perpendicular to the direction of propagation.
  • Some loudness about sound is described as the degree of sensation.
  • Which is not a wholly physical quantity but partly subjective & does not depend upon ear & listener.

Frequency & pitch

  • Frequency or pitch is defined as the number of cycles that a sounding body makes in each unit of time.
  • It is a measure of the quantity of sound.

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