Term	Definition	Demo
O.E.	Original Equipment see also OEM
Oblique Modes	See Room Resonances.
Octave	A doubling or halving of frequency. Example: 80Hz is one octave above 40Hz. In measurements and audio analysis, it is common to examine what is happening within octave or fractional-octave bands. 1/3 octave band analysis is very common, with new instruments capable of even higher resolutions. See: Real-Time Analyzer, Spectrum Analyzer.
OEM	Original Equipment Manufacturer. When one company supplies systems or components to another manufacturer for installation at the time of manufacture. For example, Harman supplies many automobile manufacturers with audio, video, navigation and other systems and components on an OEM basis. See: Aftermarket.
Ohm	Basic unit for measuring resistance and impedance.
Ohm`s Law	The basic relationship between current, voltage, and resistance. Ohm's law states that voltage = current x resistance, current = voltage/resistance, and resistance = voltage/current.
Omnidirectional	Referring to microphones or loudspeakers, having equal sound sensitivity or output, respectively, in all directions.
On Axis	In a loudspeaker it is the imaginary axis that projects perpendicular to the plane of the loudspeaker drivers. Normally it originates at the tweeter axis, or at a point close to the tweeter and midrange drivers.
Oscillator	See: Audio Oscillator
OTA	Meaning Over The Air. See: Terrestrial.
Out-of-phase	Two signals having the same waveforms that are in perfect synchronization with each other but with a perfect 180-degree phase shift at all frequencies. Equivalent to a polarity inversion of one signal. The signals will cancel each other (destructively interfere). See: Acoustical Interference, Polarity Inversion.
Overtones	Sounds with frequencies that are higher than the fundamental frequency and that normally occur with the fundamental. The first overtone is the second harmonic, since the first harmonic is the fundamental. See: Harmonic.