Detachable Face
A security system that allows you to carry the controls of the system away with you so that the system is rendered useless to anybody trying to steal it.

Hertz (Hz)
A unit of measurement, previously referred to as cycles per second. It indicates the frequency of sound or electrical wave. A unit of motion referenced to a time period of one second. The frequency of a vibration or oscillation in units per second.

Frequency Response Specification represented in Hz represents the range of sounds the system can produce. The first figure represents the lower end of the spectrum or bass, and the second figure the highs or treble. Tape players typically have a 30-15,000 Hz and CD systems extend much further from 20-20,000 Hz.

Signal to Noise (Sn) Ratio
The higher the signal to noise ratio the better. A measure of musical signal strength, relative to background noise. Unlike cassette decks that range between 50-70 dB, all CD players have an Sn ratio in excess of what is perceptible to the human ear.

Wow and Flutter
Represents the accuracy and stability of a cassette deck’s playback mechanism. The lower the percentage, the better the deck’s transport system.

Distortion
Any change or deviation from the original sound or signal fed into an amplifier.The human hearing system has a dynamic range of over 120dB. The typical threshold of pain is around 140dB, with discomfort starting around a sound level of 118dB.

Audio range
The normal audible frequency range is considered to be 15-20,000Hz. The typical hi-fi specification range is 20-20,000Hz. One has to question the validity of this range since 20Hz is more ‘feeling’ than ‘listening’, and most people can’t hear 20,000Hz (only the young). A typical telephone has a frequency response of 400-4000Hz. The human ear does not hear all frequencies at the same time.

Amplifier
An amplifier, just as the word implies, is a signal amplifier. The incoming signal from any program material source, eg CD or tape, is far too weak to power a speaker system. An amp is a device that increases the power level of a signal without distorting its wave form.

Loudness control
A volume control with special circuitry added to compensate for the normal decreased hearing ability of the human ear at the extreme ends of the audio range (when listening to lower sound levels). A typical loudness control boosts the bass frequencies and to a lesser extent the high frequencies. Sometimes this control is called contour.

Watt
A unit of measure of power. The electrical wattage of an amplifier describes the power it can develop to drive a speaker. The greater the voltage capability, the higher the wattage.

Amplifier wattage requirements are greatly dependent upon the speakers that will be used, the size of the listening area, and the average loudness that will be played through the speakers.

Continuous Power (RMS)
Represents the most conservative statement of the power of an amplifier. It is also called ‘RMS’ power. It denotes the amount of power an amplifier can deliver when amplifying a constant steady tone.

Peak Power
Peak power is used by manufacturers in an attempt to ‘look better’ in print and has no bearing on the actual performance of a product. Usually peak power works out to be twice continuous power (RMS). Some manufacturers have come up with yet another power term referred to as ‘Instantaneous Peak Power’, which is a further inflated and equally meaningless specification. Amplifier power should be judged on an equal basis when comparing one amplifier with another. Disregard any ad copy such as that just described.

Real Time Analyser (RTA)
An electronic instrument used to measure the combined response of an audio system and the area in which the system is operating. The RTA reveals what Sound Pressure Levels (SPL) are being produced by the music system simultaneously at predefined frequencies.

SPL (Sound Pressure Level)
The level or intensity at of sound at any given moment in a sound field. The deviation above and below normal atmospheric pressure is what is actually recorded. Sound pressure levels are stated in decibels.

Sound levels; Volume
Few realise that a doubling of power actually results in only a rise of 3dB. So how much more power is really needed to produce music that is ‘twice as loud’? For a complex signal such as programmed music, a 10dB change is approximately twice as loud. About 50 per cent of people can hear a 2dB change; everyone can hear a 3dB change.