O-P

O

Octave
An octave is a doubling or halving of frequency. 20Hz-40Hz is often considered the bottom octave. Each octave you add on the bottom requires that your speakers move four times as much air!

Ohm
A unit of electrical resistance or impedance.

Ohm's Law
The basic law of electric circuits. It states that the current [I] in amperes in a circuit is equal to the voltage [E] in volts divided by the resistance [R] in ohms; thus, I = E/R.

OMS (Open Music System)
System expansion for Mac OS that allows MIDI devices and Apple computers to communicate.

Out of Phase
When speakers are mounted in reverse polarity, i.e... one speaker is wired +/+ and -/- from the amp and the other is wired +/- and -/+. Bass response will be very thin due to cancellation.

Output
The sound level produced by a loudspeaker.

Overload
A condition in which a system is given too high of an input level. A common cause of distortion or product failure.

Overtones
See Harmonics.


P

PCM
Pulse Code Modulation. A means of digital encoding.

Partitions
Subdivisions of the data area on a hard disk. Every partition has its own disk drive ID.

Parts
Individual sections of a MIDI or audio track.

Passive Radiator
A device that looks just like an ordinary driver, except it has no magnet or voice coil. A passive radiator is usually a highly compliant device, with a similar cone material and surround found on regular active drivers. The radiator must usually be at least as large (or larger) than the driver it is aligned with. The passive radiator is tuned to Fb and used in place of a port.

Patch editor
Software application that provides the means to process and exchange the instrument sounds of an audio card's MIDI sound generator.

PC Card (formerly PCMCIA)
Standardized slot designed to connect hardware accessories to mobile computers.

PCI bus (Peripheral Component Interface)
Slot in the PC or Mac (bus) designed to take internal expansion cards.

Phase Cancellation
Where two oscillating frequencies move in and out of phase with each other. Chorus effects attempt to emulate this behaviour. Imagine two people playing a guitar riff. It would be very rare indeed for them to play exactly in time with each other. Where they don't, phase cancellation occurs.

Phase Coherence
The relationship and timing of sounds that come from different drivers (subs, mids, tweets) mounted in different locations.

Phase Distortion
A type of audible distortion caused by time delay between various parts of the signal.

Planar Source
Most electrostatics and magnetic planars have a large surface area. Think of a wide board dropped flat onto the water surface. The sound can be extremely coherent, but the listening window is effectively limited to being directly on-axis of both the left and right planar speaker.

Plug-ins
Unable to run on their own, these software modules plug into a sequencer, adding new sound generators or effects to it.

Point-Source
Most multi-unit loudspeakers try to approximate a point-source. Think of a pebble dropped into the water and the expanding wave pattern away from impact. Obviously it is difficult to integrate multiple point-sources into a truly coherent expanding wave. The best designs do quite well with careful driver engineering and crossover development.

Polarity
A speaker, for example, has a positive and a negative input terminal. Connecting a battery directly to the speaker will result in the diaphragm moving outward. If you reverse the battery leads, the diaphragm will move inward.

Caution: Too high of a voltage battery will also burn out the speaker!
Ported Enclosure:
A type of speaker enclosure that uses a duct or port to improve efficiency at low frequencies.
Power (P)
The time rate of doing work or the rate at which energy is used. One equation for Power:
P = Volts^2 / Impedance

PowerBook
Product name for mobile Apple computers.

Processor
Highly complex arithmetic unit built into a chip - the brain of a computer, so to speak.

Push-Pull Configuration
One driver is mounted normally, the second is mounted so that it faces into the enclosure, both sharing the same internal volume and wired out of phase with one another. Although electrically out of phase with one another, the drivers are acoustically in phase since they move in the same direction. This alignment theoretically reduces second order harmonic distortion.

Push-pull
Most common type of amplification that amplifies the negative and positive sides of the waveform separately. Allows for much higher power output than single-ended.

Pre-amplifier
Or Pre-amp is a device that takes a source signal, such as from a turntable, tape-deck or CD player, and passes this signal on to a power-amplifier(s). The pre-amp may have a number of controls such as source selector switches, balance, volume and possibly tone-controls.