RDS - RDS stands for Radio Data System. Radios with RDS tuners can automatically tune in stations according to the types of music format they broadcast. Some RDS equipped tuners can even override CD playback when traffic or emergency alerts are broadcast. RDS receivers can display text messages and even graphics (usually call letters and format information) that is on a subcarrier signal within the normal broadcast signal.

Radio Frequency Interference (RFI) - Electromagnetic radiation which is emitted by electrical circuits carrying rapidly changing signals, as a by-product of their normal operation, and which causes unwanted signals (interference or noise) to be induced in other circuits.

Random Play - Also called Shuffle Play. This function randomizes the order of selections during playback in CD players and changers.

RE (a Theile Small parameter ) - Also called DCR - The Direct Current resistance (not impedance) of a speaker's voice coil as measured with an Ohm Meter.

Reactance - Frequency dependent resistance produced by a coil (inductor) in an AC circuit like the output of an amp. This inductive loading will allow all dc current to pass without change, but will attenuate higher frequencies.

Remote Turn On Lead - Also may be labled REM. A switched 12V+ lead from the headunit. This lead is connected to the Remote (turn on) terminal of the power amp(s) so they will turn on and off with the headunit. DO NOT use this lead for the main amp power.

Resistance - Most all conductors of electrons exhibit a property called resistance. Resistance impedes the flow of AC or DC current. It is measured in units called Ohms.

Resistor - An electrical component that exhibits a specific amount of resistance on a circuit. The higher the value of resistance (measured in ohms ) the lower the current will be in the circuit.

Resonance - The tendency for a mechanical or electrical systems to vibrate or resonate sympathetically at a certain frequency when stimulated by external energy. Every element and material has a particular natural resonance point.

Resonant Frequency - The frequency at which a speaker cone vibrates with the least inertia. Also refers to the frequency that produces an object's natural resonance point.

Reverb - A blend of multiple interacting sound reflections within an enclosed space that, when combined with the direct sound from a source, defines the character of the sound in that area (like a room or hall). It also refers to a signal processor that simulates natural reverberation.

RF Modulator - A device that converts an input signal (typically audio and/or video) into a radio frequency. This allows the signal to be received by a tuner so it can be played through a system that has no inputs for it.

Ringing - The tendency for any vibrating surface to continue to produce a particular frequency naturally, even when it is not present in the input signal.

Rms (a Theile Small parameter ) - The losses due to the speaker's suspension.

RMS (Root Mean Square) - A formula that provides a reasonably accurate means of measuring and comparing continuous AC power.

Roll Off - A graduated attenuation (turning off) of audio output above and below certain specified frequencies.

Room Response - The sound characteristics a speaker has when placed in a listening space (room). This is influenced by various conditions such as the reflective qualities of the space, the shape of the space and where the speaker is positioned in the space.