Echo
A reflected sound wave. It is more in places that have harder and smoother surface.
Elasticity
The ability of a material to bounce back after being disturbed. Gases are generally not very elastic.
Decibel
A unit to measure the loudness of sound. It is usually represented by symbol dB.
Each 10 dB increase in loudness represents a 10 fold increase in the intensity of sound.
Ultrasound
The word 'ultra' means beyond. Ultrasounds are sounds with frequencies above the normal human range of hearing.
Infrasound
The word 'infra' means below. Infrasounds are below the range of sounds that can be heard by humans.
Doppler Effect
The change in frequency of a wave as its source moves in relation to an observer. It is named after the Austrian scientist Christian Doppler (1803 - 1853).
Shock Wave
A shock wave forms when a plane goes faster than the speed of sound. Shock waves release huge amount of energy and people hear it as a sonic boom.
Acoustics
The study of how sounds interact with each other and the environment. It is used in designing the concert halls to control reverberation and interference.