Sound is a longitudinal wave that travels through mediums like solid, liquid, gas and it is produced due to vibration of an object. Sound cannot travel in a vacuum.

Sound travels faster in a hot medium. It is much faster in a solid than in a liquid or gas. It also travels faster at sea level (where air pressure is higher).

 Humans can characterize sound by frequency, amplitude, and tone.

Sound produced by any means has characteristics like loudness, pitch, or shrillness, and quality or timbre.

  • The loudness of the sound is the measure of the sound energy reaching the ear per second.
  • Pitch is the brain’s interpretation of the frequency of an emitted sound.
  • Tone is a measure of the quality of a sound wave.
  • Quality or timbre of a  sound wave is that characteristic which helps in distinguishing between two sounds of same loudness and same pitch.
  • The amplitude of a sound determines its volume (loudness).

characteristics of sound 

Loudness – It is the property by virtue of which a loud sound can be distinguished from a faint one, both having the same pitch and frequency. Loudness is expressed in a unit called decibel (dB). It is directly proportional to the amplitude of vibration.

Intensity – The amount of sound energy passing each second through a unit area is called the intensity of sound.

Pitch – Pitch is that characteristic of sound by which an acute (or shrill) note can be distinguished from a grave or flat note. It is not the same as frequency. It refers to the sensation as perceived by the listener.

Quality / Timbre – The quality or timbre of the sound is that characteristic which enables us to distinguish one sound from another having the same pitch and loudness, but emitted by two different instruments.


Loudness & Intensity

  • Loudness and intensity are not the same
  • Loudness is a measure of the response of the ear to the sound
  • Even when two sounds are of equal intensity, we may hear one as louder than the other simply because our ear detects it better
  • Loudness is a subjective quantity while intensity, being a measurable quantity, is an objective quantity for a sound wave
  • L = K log I where L is the loudness, I is the intensity and K is the constant of proportionality


Factors affecting the loudness of sound


  • Loudness depends on the surface area of the vibrating body
  • The larger the vibrating area the louder the sound heard
  • Loudness depends on the density of the medium
  • More the density of medium more is the loudness
  • Loudness depends on the presence of resonant bodies
  • The presence of resonant bodies near the vibrating bodies increase the loudness


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