Last modified on 28 March 2013, at 15:39

Physics Course/Sound

Sources of Sound

In everyday life , Sounds come from many different sources

  1. Human's voice . Talking , screaming , shouting ...
  2. Animal's Sound . Dog barking , Bird Chirps ...
  3. Music Instruments . Music sound from guitar , drum
  4. Noise . Noise from collision of two things like two collides with each other

Characteristics of Sound

Sound produce when two object collides with each other . The Loudness of the sound depend on the collision of two objects . The Tone of the sound is trebble or bass depends on material's types and material occupied space volume

  • Sound that is audible to human's ear are in the frequencies range 2Khz - 20 Khz . Sound of frequency above 20KHz is called Ultra Sound . Sound of frequency below 2KHz is called Infra Sound
  • Sound does not exist in vaccum . No sound exist when placing a bell without air
  • Sound needs matter's materials in order to spreading . Velocity of sound will be changed when sound travels through different medium . Fast in Solid, then Liquid and then Gas
  • In air sound travel at a changing speed depend on the air's Pressure and Temperature . At standard atmosperic condition sound travel at speed v = 300 m/s
  • Sound wave is a Longitude Wave travels with velocity changes with Temperature and Pressure of the medium it travels through .
Sound wave travels in air , Sound's Pressure creates expanding or shrinking colums of air called Rare Fractions . | || | ||
  • The Reflection of sound's wave occurs when sound wave is being reflected back by a blocking object into the medium it comes from . Provided that the height of a blocking object is greater than the wave's wavelength . The total reflection occurs when the incident angle equals to the reflection angle
  • When two sound waves travel toward each other, two waves interfere Constructively or Destructively to produce different Interference Effects or Sound Effects like Noise , Echo , Intermittent , No Sound

Applications

Communication

Audible sound wave is converted to electrical wave Then the electrical wave can be processed further by adding amplification and volume control ... before electrical wave is converted back to Audible Sound

Audible Sound Wave --> Electrical Wave --> | Amplyfy --> Volume Control | --> Audible Sound

Telecommunication

Audible sound has frequency range 2KHz - 20 KHz cannot travel further than 3m . In order to carry audible sound over a long distance from the Transmitter to Receiver through Air . Sound Wave needs to be mixed with a carrier wave of high frequency MHz . This process is called modulation. There are three modulation methods are used in telecommunication namely AM Modulation , FM Modulation and PM Modulation

At Emitter's Station

Audible Sound Wave + Carrier Wave --> AM Wave , FM Wave or PM Wave --> Amplify --> Transmitter's Antenna

At Receiver's Station

AM Wave , FM Wave or PM Wave --> Receiver's Antenna --> Demodulate -- > Audible Sound


In AM Modulation sound wave is enveloped and mixed with high frequency carrier wave such that the amplitude of the carrier wave varies with sound wave's amplitude . In general , AM wave is easy to be interfere with other sound waves in the medium travel through therefore the quality of sound is not very good . AM sound wave cannot travel very far . AM wave is usually use to transmit sound in local area . AM's spectrum on Radio receiver KHz


In FM Modulation sound wave is mixed with high frequency carrier wave to generate a wave of three frequencies fs - fc , fc and fs + fc. In general , FM wave is not easy to be interfere with other sound waves in the medium travel through therefore the quality of sound is very good . FM sound wave can travel very far . FM wave is usually use to transmit sound through a long distance . FM wave is usually use to transmit sound globally or internationally . FM's spectrum on Radio receiver MHz

Reference

  1. Sound