Satellite Radio - Digital radio transmission system that utilizes satellites in space to broadcast directly to ground based and mobile receivers. Two existing networks, Sirius and XM offer hundreds of channels of diverse offerings for a subscription fee.

Sampling - Measuring the analog signal at a fixed rate of speed (sampling frequency) for digital conversion.

Sd (a Theile Small parameter ) - Effective piston radiating area of a subwoofer driver (actual surface area of the cone) in square meters or centimeters.

Sealed Enclosure - Also called Acoustic Suspension. A sealed or closed box speaker enclosure. For details and more enclosure types see Woofer Enclosure Designs.

Selectivity - Tuner specification which defines the tuner's ability to reject adjacent station interference.

Sensitivity (Speakers) - Also referred to as Efficiency. A rating (measured in dB) that illustrates how effectively a speakers uses the power supplied to produce an output. As in amplifiers, it's a ratio of power in verses power out. The most accepted standard to determine this rating is measuring the output of the speaker 1 meter away from it, giving it 1 watt of full audio range (pink noise) input.

Sensitivity (Radio Tuner) - The relative sensitivity to the reception of RF signals in a tuner measured in dBf. Normal is around 10 to 14 dBf (The lower the number the better).

Separates - A speaker system with more than one type of driver (per channel reproduced). The most common type of separates system is a set containing a high frequency driver (tweeter) and a lower frequency driver (mid or woofer), and a passive crossover network. Separate woofers or mids may be easier to mount in tight places because tweeter protrusion is not a factor. Separate tweeters allow more positioning options to acheive better imaging.

Series Wiring - A wiring configuration in which the speakers are basically hooked up in a loop. Think of the terminals on your woofer as an entrance (+ terminal) and an exit (- terminal). The signal (from the positive amp terminal) enters the first woofer (+) and exits go in the next woofer (+) and out (-). Follow this pattern until you're to the last woofer. At that point you hook the (-) terminal of the woofer to the (-) terminal on the amp. For examples, see Speaker Wiring Diagrams.

Shield - An outer metallic foil or braided wire layer surrounding a conductor(s) which is designed to prevent electrostatic or electromagnetic interference from external sources.

Signal - Any electrical transmittance that conveys data.

Signal processors - Active devices which alter a signal either to achieve a particular effect or to solve a sonic problem. (ie: time delays, equalizers).

Signal To Noise Ratio - Also called SN Ratio. A measurement of noise level in a device compared to the level of the signal. This ratio is expressed in dB. Higher numbers signify a greater difference between the two, which is better.

SIRIUS - A satellite radio subscription service that broadcasts over 125 digital-quality channels, including 67 channels of 100% commercial-free music, plus over 60 channels of sports, news, talk, entertainment, traffic, weather and data.

Slew Rate - Slew rate measures the ability of a piece of audio equipment to accurately reproduce fast changes in amplitude. Measured in volts per microsecond, this spec is most commonly associated with amplifiers. An amplifier with a higher slew rate delivers sound quality that is tighter and more dynamic.

Slope - The rate of change that a frequency response curve displays, normally stated in dB per Octave. Slopes are most commonly used to reference crossover rates.

Sound - Also reffered to as Acoustical Energy. Fluctuaton of air (wave) that changes internal ear pressure, producing an auditory sensation.

Sound Field - The total acoustical characteristics of sound as presented by an audio system and interacting with the space (room or area) it is in.

Sound Pressure Level (SPL) - An acoustic measurement of sound energy, typically expressed in dB. 1 dB SPL is the smallest increment in sound level to which the average human is sensitive

Soundstage - Individual vocal and instrumental "images" make up your stereo system's soundstage. The degree to which particular sounds can be localized in space is an indication to the quality of the imaging. The better the soundstage, the greater the sense of its depth, height, and width.

SPDT (Single Pole Double Throw) - A relay or switch that has only one contact (pole) but whose contact can throw or make electrical contact with two separate stationary contacts.

Spider - The rear suspension element on the cone of a loudspeaker (click here for Speaker parts diagram).

SPL (Sound Pressure Level) - An acoustic measurement of sound energy, typically expressed in dB. 1 dB SPL is the smallest increment in sound level to which the average human is sensitive.

SPST ( Single Pole Single Throw) - A relay or switch that has only one pole or contact and can only throw or make electrical contact with one stationary contact.

Stamped (Speaker Frame) - The frame or basket of a loudspeaker made of steel which has been stamp pressed to achieve its shape.

Standing Wave - These are created when a sound is reflected between two parallel or adjacent surfaces. When the reflecting sound waves interfere with each other (frequency dependent), some sounds are made more intense and others diminished in given parts of a listening environment. The places are sometimes called peaks and nodes.

Stereo - A method of recording and playback through an audio system consisting of two or more audio channels to give a more natural distribution of sound.

Streaming - A technique for transferring data so that it can be processed as a steady and continuous stream. Commonly used on the Internet, the client browser or plug-in can start displaying the data before the entire file has been transmitted. This overcomes the problem of not having fast enough access to download large multimedia files quickly.

Stroke - The distance that the speaker / woofer voice coil can travel in both directions.

Subwoofer - A speaker made to reproduce the lowest of audio frequencies, usually in the range of 200 Hz and down.

Subwoofer Preamp Outputs - 1 or 2 line level RCA outputs whose signal has passed through a built-in low-pass crossover for connection to a dedicated subwoofer amplifier.

Supraaural - A term used in reference to headphones. Supraaural phones rest on the ear, rather than enclosing the ear.

Super Tweeter - A Driver constructed to reproduce the highest possible frequencies from approximately 13 kHz to 25 kHz, extending beyond the range a normal tweeter (usually up to 20 KHz) can comfortably go.

Surface Mounting - A method of placing speakers in a housing or enclosure so they do not require any mounting depth and can be mounted on top of a surface.

Surround - The surround's main purpose is to keep the front part of the diaphragm (cone) centered as it moves in and out. They are usually constructed of foam or rubber.It is part of the suspension system for the cone, but provides little restoring force compared to the spider. For a speaker like a woofer that has a long travel (Xmax) to their cone, the surround will need to be longer (click here for Speaker parts diagram).

Sweet Spot - The spot or position in a listening space where optimum imaging is most convincingly achieved, producing the highest level of a realistic and believable audio experience that the speaker system can reproduce.

Switch - A switch is any form of mechanical, electronic, electromechanical, magnetic, or mercury device that either opens or closes a circuit.