Radar Sensor - A common name for a type of spatial sensor used in automotive security system’s to protect/monitor open areas (such as convertibles, truck beds, etc.).
Radio Data System (RDS) - RDS scrolls text on the head unit display to help sort broadcast by type (talk ,sports, etc.) and provide drive-time warnings of accidents.
Range - In audio this is usually described as frequency range, this is a system’s frequency response, beyond which the frequency is attenuated below a specified tolerance. Also, the frequency band within which a receiver or component is designed to operate. In security the term used to quantify the maximum operating distance that can exist between a vehicle and the remote control transmitter. Range is usually expressed in feet or yards.
Rarefaction - A state or region of minimum pressure in a medium traversed by compression waves (sound waves).
Ras - Acoustical equivalent to RMS.
RCA - Radio Corporation of America
RCA Connector - A plug and socket for a coaxial cable. They are found on all old audio/video devices and many new ones that continue to support analog signals. They are also used for digital signals.
RDS - Refer to Radio Data System
Re - Refer to Resistance
Reactants - Something that takes part in and undergoes change during a reaction.
Real-Time Analyzer (RTA) - A spectrum analyzer that measures the amplitude versus frequency (X vs. Y plot) of an audio signal while in real time.
Rear Fill - A term used typically when referring the rear speakers or music audibly heard from the rear. This music is usually a bit less aggressive and not as easily heard as the front stage.
Receiver - A device designed to receive a signal or command from a source such as a transmitter.
Receiver (Rx) - A receiver mostly refers to that part of a device that receives signals; often, the device acts as both a transmitter and a receiver (transceiver) such as in the case of cell phones (cellular radio) and antennas used for data communication.
Recone - This term refers to replacement part(s) or sometimes a kit, that is necessary to repair a blown or damage subwoofer.
Rectification - The process of turning AC into (pulsing) DC. Modern alternators use a process called Full Wave Rectification with minimum of 6 diodes.
Red/Blue/Green RGB - This refers to an analog video signal transfer where the primary colors of red, green and blue each have their own conductor. RGB signals in automotive applications have three different variations: RGBS, RGBHV, and RgsB. The main differences are how the conductor that controls picture information synchronizing is implemented.
Relay - The most commonly used relay in the world of car audio and security is the Single Pull Double Throw (SPDT) relay.
Relay Isolator - An electrical device that divides direct current (DC) into multiple branches and only allows current in one direction in each branch.
Remote - A common name for the remote control unit transmitter used with a remote security system.
Remote Turn-On - The discrete turn-on circuit in most mobile electronic audio products. After market headunits typically have a remote turn-on output whereas preamp level processors and amplifiers typically have remote turn-on input.
Res - The electrical resistive equivalent of RMS.
Reset - The ability of a security system to automatically stop sounding the siren and return to an armed state after being triggered, as long as no further trigger conditions are present.
Resistance (Re) - Driver DC resistance, mainly voice coil impedance at rest.
Resistor - A device having a designed resistance to the passage of an electrical current.
Resonant Frequency (Fs) - The frequency of resonance in a given driver when in free air. This can be typically related to the optimal frequency in which to tune the driver to, or around.
Reverb Time -60dB (RT-60) -
Revolutions Per Minute (RPM) - Refers to a vehicle’s engine revolutions.
Rg - Amplifier source resistance (includes leads, crossovers, etc.).
RGB - Refer to Red/Blue/Green
Ripple - In acoustical response this is the deviation from a flat response in the pass band, generally used to describe vented subwoofer enclosure characteristics. With the charging system this is the amount of Alternating Current (AC) present on a DC circuit’s power line.
RMS - Refer to Root Mean Square
Root Mean Square (RMS) - Literally "root mean square." A DC voltage that will produce the same heating effect (power output in Watts) as the AC voltage. For a sine wave, the RMS value is equal to 0.707 times the peak value of an AC voltage. Example: divide Peak-to-Peak by 2 (or in half) and multiple by 0.707 = RMS voltage.
Roll-Off - Relating to the attenuation of frequencies, above or below a given point, at a specific rate.
Roll-Off Frequency - The steepness of a transmission function with frequency, particularly in electrical networks analysis, and most especially in connection with filter circuits in transition between a passband and a stopband. Roll-Off Frequency is the point in which this happens.
Roof Mount Antenna - A permanently-installed antenna located on the vehicle’s roof. Communication antennas are commonly roof mount applications (except for convertibles).
Route Guidance System - A GPS based, electronic guidance system installed into vehicles using digital mapping and point of interest information to facilitate getting from a location to the desired destination with precise directions. This is generally an installed item whereas a handheld (portable) navigation system is often called a PND.
RPM - Refer to Rotations Per Minute
RT-60 - Refer to Reverb Time -60dB
RTA - Refer to Real-Time Analyzer
Rx - Refer to Receiver (Rx)