Haas effect: a psycho-acoustic phenomenon in which precedence is given to the direction of the first arrival of direct sound in attributing the direction from which the sound is coming.

Hair cells: biological cells in the cochlea of the inner ear where vibration is turned into a neural signal, which is transmitted to the brain.

Hard ground: ground such as concrete, most other paving materials, and water which is considered to be an acoustically reflecting surface, in contrast with ‘soft ground’ which is considered to be sound absorbing.

Harmonic: a signal having repetitive pattern.

Harmonoise: an integrated method for predicting environmental noise throughout Europe, which may replace individual national methods such as CRTN and CRN.

Hearing level: a measured threshold of hearing, expressed in decibels relative to a specified standard threshold for normal hearing.

Hearing loss: any increase of an individual’s hearing levels above the specified standard of normal hearing.

Helmholtz resonator: a vibrating system having a single degree of freedom; it consists of an air-filled enclosure connected to the open air by a narrow column; the air in the enclosure acts as the spring and the air in the column acts as the mass.

Henry (H): the unit of electrical inductance.

Hertz (Hz): the unit of frequency; the number of cycles per second.

High pass filter: a filter, which transmits frequency components of a signal that are higher than a certain cut-off frequency but which attenuates those below the cut-off.

HML method: a method for estimating the A-weighted sound pressure level at the ear when hearing protector is being worn based on the attenuation provided by the protector at high (H), medium (M) and low (L) frequencies.

Hyperacusis: unusual sensitivity and discomfort caused by sounds which are usually tolerable to other listeners. The condition can sometimes be associated with hearing loss.

Hysteresis damping: a type of damping that occurs within materials as a result of phase changes which occur between stress and strain during the vibration cycle.