Impact Sound

A sound with a very sharp attack, by analogy to the collision of an object in motion with another object at rest or in motion. Also called impulse sound.

Compare: Click, Pulse, Transient.

For sounds of intensity 75 - 90 dBA, the ear has a protective mechanism to reduce its sensitivity to low frequency impact sounds by changing the mode of oscillation of the bone structure in the middle ear (see ossicles). However, a delay of 300 to 500 milliseconds is required to set this protection fully in operation (compare threshold shift). Most naturally occurring impact sounds have longer rise times, and thus the ear can easily cope with them, but many man-made sounds, such as explosions from artillery or guns, as well as certain industrial noises, can have such sharp attacks that the ear's protective mechanism cannot respond quickly enough. The hearing loss caused by such sounds is permanent. Acoustic trauma and related damage suffered by soldiers in wartime is called shell-shock.

See: Recruitment, Transient Response.

The peak level of an impact sound may be measured with the fast response mode of a Sound Level Meter. For further discussion see damage-risk criteria. Impact sounds may also be analysed with an impact noise analyser.

See: Impact Insulation Class, Sound Insulation.