Glossary of Terms - O

A glossary of terms covering lighting, audio, vision and staging in the event and theatrical industry.

O

There can be a number of meanings for some terms which can vary from country to country and manufacturer to manufacturer. Information within this guide is indicative and every situation can require a different approach and solution. All care has been taken, however, Image Group NZ accepts no responsibility for inaccuracies. If you have any suggestions, comments or queries regarding this list please contact us.

OCTAVE
The interval between any two frequencies having a ratio of 2 to 1. Example: "A 440" is an octave above "A 220".

OFFSTAGE

    A movement towards the nearest side of the stage from the centre. (e.g. "Focus that spot offstage a bit please")
    The area out of sight of the audience (e.g. "Get that donkey offstage!")

OHM
The unit of electrical resistance, equal to the resistance through which a current of one ampere will flow when there is a potential difference of one volt across it. Ohm is the unit of measure used to express opposition to current flow. Every wire or part through which electricity passes has some resistance to that passage.

OHP
See OVERHEAD PROJECTOR

OMNIDIRECTIONAL
A term usually applied to microphones to refer to uniform pickup of sound from all directions.

ONSTAGE
A movement towards the centre of the stage from the sides.

OPEN WHITE
(o/w) Lighting with no colour filter.

OSCILLOSCOPE
A test instrument that shows a picture of electrical waveforms by means of a cathode ray tube. An oscilloscope is calibrated to allow measurement of the instantaneous values and waveforms of electrical signals that are changing rapidly or varying as a function of voltage or time. Also known as a Scope.

OSD
On Screen Display.

OUTPUT IMPEDANCE
The internal output impedance of an amplifier presented by the amplifier to the load. (not to be confused with load impedance.)

OUTPUT POWER
The power delivered by a system to its load. (i.e. an amplifier driving a loudspeaker system)

OUTRIGGER
An extendible leg to increase the stability of access equipment (eg Tallescope, Scaffold tower).

OVERHEAD PROJECTOR (OHP)
A device consisting of a light source, a transmissive or reflective platform, and a focusable lens assembly. An OHP is designed to project images from tranparencies onto a screen. LCD projection panels are designed to be used with transmissive OHPs and work best with OHPs that produce at least 3,000 lumens. Since 5% to 10% of the light that shines through an LCD panel gets onto the screen, a 3000 lumen OHP will produce an image of 150 to 300 lumens. Transmissive OHPs are fairly bulky (bigger than many projectors). Reflective OHPs are fairly portable but are not useful with LCD projection panels.

OVERTONE HARMONIC
Multiples of frequency of a fundamental waveform.

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