ASTM E 1130 - Standard test method for objective measurement of Speech Privacy in open offices using the Articulation Index.
Active acoustics Sound - Electronically generated background sound of a specified level and frequency content, that is introduced into occupied environments to provide masking of intrusive noises and to enhance speech privacy.
Amplifier - An electronic device used in sound system applications to convert a low level signal such as from a microphone or CD player into a high-power signal (rated in watts) capable of powering a loudspeaker to a high sound level.
Analog - In sound system applications, an analog electrical signal represents the measured sound level in its exact continuous form. Likewise, an analog device is an electronic device that processes analog signals in their continuous form.
Directivity Index - A measure of the angular direction of the sound radiation from a loudspeaker, presented as a dB level either higher or lower than that which would be radiated by a spherical sound source.
Dispersion - Refers to the way in which sound spreads outward from a loudspeaker in a sound systems application. Dependent on the directivity index and the distance away from the speaker.
Exciter - The electro-mechanical device which converts an electrical signal from the amplifier into a mechanical vibration of the loudspeaker radiator, causing a sound wave to be produced with the same characteristics as the electrical signal. Also called a transducer.
Octave - A frequency interval wherein the higher frequency is twice the lower frequency.
Octave Band - The audio frequency range is generally separated into octave bands as a matter of convenience, wherein each specific band is represented by its center frequency, e.g. 63 Hz, 125 Hz, 250 Hz, 500 Hz 1 kHz, 2 kHz, 4 kHz, 8 kHz, and 16 kHz, which cover most of the audible frequency range.
Ohm - Unit of electrical resistance; e.g. most loudspeakers are typically 8 ohms.
Pink Noise - Electronically generated sound that has equal energy in each octave band; typically used as the basis for the post-filtered signal used as masking sound.
Polar Pattern - The graphical representation of the coverage of a loudspeaker at various frequencies.
Privacy Index (PI) - A measure of speech privacy, or lack of speech intelligibility, where the PI is calculated from the Articulation Index (AI) according to the following: PI = (1 - AI) * 100%.
Processor - A general term used in sound system applications to describe an electronic device that may have the following functions: signal generation, signal conditioning, equalization, and mixing.
Sound Masking - The process by which masking sound is implemented to cover unwanted or intrusive sound (i.e. speech, equipment noise, etc.) and to enhance speech privacy.
Sound Spectrum - A representation of a sound wave (time varying pressure wave) showing the frequency content and amplitude of the sound over the audio frequency range.
Speech Privacy - Refers to the lack of speech intelligibility from adjacent talkers. Several levels of speech privacy are defined in the ASTM standards, from Confidential privacy (meaning speech sounds can be heard but not understood), to Normal privacy (meaning that speech can be occasionally heard and understood but is generally non-intrusive), to Poor privacy (wherein all adjacent speech can be heard and understood). These levels can be related to ranges of PI representing each level of speech privacy.
Transformer Tap - Refers to the power setting available on a step-down transformer (e.g. 1 watt, 2 watt, 4 watt, etc ) used in high voltage distributed sound systems (e.g. 70v, 50v, and 25v amplifier systems).
Volt - Unit of potential difference or electromotive force. One volt is the potential difference needed to produce one ampere of current through a resistance of one ohm. Voltage is the driving force throughout a sound system from the microphone input to the speaker terminals.
Watt - Unit of electrical power required to do work at the rate of one joule per second. One watt of power is expended when one ampere of direct current flows through a resistance of one ohm. The power capability of amplifiers and loudspeakers is given in watts, which relate to both the voltage driving the system and current handling capabilities of the devices.
White Noise - Electronically generated sound that has equal energy at each frequency so that the octave band level increases by 3 dB for each increase in octave; white noise is typically perceived to sound "hissy" compared to pink noise.