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Alto
Alto
From the Italian, meaning ‘high’. It applies to singing. It is the vocal range above the tenor. Female alto voices (see: Human voice) are often called contralto.
Alto musical instruments such as the alto saxophone, alto clarinet and alto flute also have a high range of notes. (See also: Bass; Tenor; Treble.)
Amplifier
Converts a low-power signal from a pre-amplifier into the high-power signal (tens to hundreds of watts) needed to drive a loudspeaker.
Amplitude
The height of a wave (light wave or sound wave) as seen on a trace. It is a measure of the brightness of a source of light or the loudness of a sound.
This is a wave with a small amplitude.
This is a wave with a large amplitude.
Amplitude – The height of a wave shows the amplitude.
Anechoic chamber
A room where the walls, ceiling and floor have been covered with sound-absorbing material to stop reflections. It has ‘dead’ acoustics. It is useful in testing equipment such as loudspeakers to find out their real characteristics.
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Angle of incidence
The angle at which a ray of light approaches a mirror or transparent material, such as a block of glass.
Angle of reflection
The angle at which a ray of light leaves a mirror. It is always the same as the angle of incidence.
Angle of refraction
The angle at which a ray
of light bends when it goes across the boundary between two transparent substances, such as air and glass. The ray is made steeper when it enters a denser substance such as water. (See also: Refraction of light.)
Angle of incidence/Angle of reflection – When light rays arrive at a mirror, the angle of incidence is equal to the angle of reflection. Both are measured with respect to a line drawn at right angles to the mirror.
Mirror
Angle of incidence, i
Angle of reflection, r
i=r
Angle of refraction – When light enters a transparent block or liquid, the light is bent downwards. The angle between the light ray and a line at right angles to the surface is the angle of refraction.
Glass block
Angle of incidence
Angle of refraction
