Collection: Glossary of Terms

Acoustic Suspension – A sealed speaker enclosure.

Alternating Current (AC) – An electrical current that periodically changes in magnitude and direction.   Audio signal is passed from one device to another in AC.

Ampere (A) – The unit of measurement for electrical current in a circuit.

Amplifier (Amp) – A device which increases signal level from one device to another.  Like from a head unit to a speaker.

Attenuate – To reduce in level.  To turn down the volume.

Audiophile – A person interested in the accurate reproduction of sound or music.

Baffle – A surface used to mount a loudspeaker.  Like the front panel of an enclosure.

Balance – The relative volume level between two channels, usually the left and right channels.  To make the same or equal.

Bandwidth – The total frequency range of any system.  Human audible bandwidth is typically defined as 20 Hz – 20,000 Hz.

Band-pass EnclosureA multi-chambered ported system.

Band-pass Filter – An electric circuit designed to pass only middle frequencies.

Basket The rigid frame of a speaker that supports all of its components.

Bass– The low audio frequency range typically below 500 Hz (hertz).

Bass Reflex – A speaker in an enclosure that uses a vent or port to gain low frequency response.  A vented enclosure.

Bi-amplify – To use two amplifiers or channels to run the lows and the highs separately in a speaker system.

Bridging– Combining two outputs of an amplifier to use as one, usually to a woofer. This provides an increase in power output (wattage) necessary to reproduce lower frequencies at higher volume levels.

Capacitor – A device used to store electrical energy.  Most commonly used to maintain a set amount of energy at a power supply or circuit.

CircuitAny closed path followed by electrical current.  A configuration of electrically or electromagnetically connected components or devices.

Circuit BreakerA device that protects electric circuits by interrupting power in a circuit when an overload occurs.  Unlike a fuse a circuit breaker is reset able.  Rated in amperes (amps).

Clipping – Refers to a type of distortion that occurs when an amplifier is driven into an overload condition.  This typically happens when the gains are set above the level of the signal input.  This distortion causes and excess of high-frequency energy to be sent to the speakers.  Hard clipping will result in damage of the speaker.

Cms – The mechanical suspension compliance of a speakers spider and surround.

Coaxial – A speaker type that utilizes a tweeter mounted at the center of a woofer cone. The idea is to have a wide bandwidth of frequencies coming from the same source.

ConeThe radiating surface of a loudspeaker referred to as the part that moves the air.

Crossover – A frequency divider used to route various frequency ranges to different speakers.  Crossovers can also be used to maintain impedance loads and adjust output levels.
Crossover Slope – The amount of roll off a crossover point has measured in decibels per octave.  These roll offs are ranked in orders, the smallest being 1st at 6 dB/oct.  That means that the crossover point rolls off at 6 decibels per every octave.  Each order steps up by 6 decibels.  A steep slope is 6th order which rolls off at 36 dB/oct.

Current (I) – The flow of electrical charge measured in amperes.

Damping (Damping factor) – Refers to the control an audio component has to stay in sync with the signal and to stop when the signal stops.  In other words, it’s the amount of control an amplifier and speaker have to accurately reproduce the signal.  If the amplifier has over damping, the signal never reaches its full peak and sounds cut off.  If the signal sounds muddy or distorted, it may be under damping.  Good damping results in reproducing the signal just as it was recorded.

Decibel (dB) – The measurement of audible loudness.
0 dB is the threshold of hearing, 130 dB is the threshold of pain.
Whisper: 15-25 dB
Quiet background: about 35 dB
Normal home or office background: 40-60 dB
Normal speaking voice: 65-70 dB
Orchestral climax: 105 dB
Live Rock music: 120 dB+
Jet aircraft: 140-180 dB

Direct Current (DC) – Current that moves in only one direction.  The power system in automobiles is DC, typically a 12 VDC system.

Distortion – Anything that alters or disrupts an audio signal.

Dome A convex speaker shape usually used for tweeters.

Driver– Synonymous with loudspeaker.  Term used when talking about a speaker.

Dual Voice Coil (DVC) – A voice coil with two windings, generally used in woofers. Each voice coil can be connected to a stereo channel, or both voice coils can be wired in parallel or series to a single channel.

Efficiency– The ratio of energy output to total energy input, expressed as a percentage.

Farad – The basic unit of capacitance.  Used to describe how much storage capacity a capacitor has.

FidelityThe term used to describe the accuracy of recording, reproduction, or general quality of audio processing.

FilterAn active or passive circuit or device designed to block a certain frequency or range of frequencies.

Flat Response – An accurate reproduction of a given audio signal.

Floating Ground– Non-common grounding point.

Free Air Resonance – The resonant frequency of a speaker when outside of an enclosure.

Frequency– The number of wavelengths which pass a specific point in a specific time period, measured in Hertz (Hz).  Cycles per second.

Frequency Response The lowest and highest parts of the frequency spectrum that can be reproduced by an audio component within specific limits and tolerances.

Full-range – A speaker designed to reproduce all or most of the sound spectrum.

Fuse– A device that protects electric circuits by interrupting power in a circuit when an overload occurs.  Rated in amperes (amps).

Gain – The level control of an audio signal.  To increase in volume.

Gauge (wire)The diameter of a wire.  The higher the number, the thinner the wire.

Golden Ratio – A ratio of depth, width, and height for a speaker enclosure or listening room.  Based on the Greek Golden Rectangle and often referred to as the perfect dimension ratio for acoustics.
W = 1.0        Depth = 0.618        Height = 1.618

Ground An electrical line with the same electrical potential as the chassis of the vehicle, most commonly negative 12 volts DC.

Ground Loop– The condition created when two or more paths for electricity are created in a ground line, or when one or more paths are created in a shield or an audio cable.  This can create undesirable noise such as a high pitched whine when the vehicle is running or pops and clicks when other devices are used in the vehicle.

Ground Potential In an automobile this is the electrical potential of the vehicles chassis, specifically the chassis of the alternator when the vehicle is running.  A circuit, terminal or chassis is said to be at ground potential when it is used as a reference point for other potentials in the system.

Hertz (Hz) – A unit of measurement denoting frequency, originally measured as Cycles Per Second, (CPS): 20 Hz = 20 CPS. Kilohertz (kHz) are hertz measured in multiples of 1,000.

High-Pass Filter – A circuit that allows high frequencies to pass but rolls off the low frequencies.  Typically used with component or coaxial speakers to roll off the lower frequencies.  This allows those speakers to play louder with less distortion that is normally caused by the lower frequencies.

Imaging – Listening term.  Describes audio that has audible width, depth, and height or a holographic re-creation of the signal.

Impedance The opposition to the flow of alternating current (AC) in a circuit.  Measured in ohms.

Infinite Baffle – A speaker baffle that separated the front and back sound waves of a speaker without using an enclosure.

Kilohertz (kHz) – One thousand hertz.

Load– The electrical demand of a process, expressed in current (amps), power (watts), or resistance (ohms).

Loudness Control Intended to boost low frequencies at lower volume levels and should not be used at high volume listening levels
Loudspeaker An electro acoustic transducer which converts electrical audio signals at its input to audible waves at it’s output.  May also refer to a given driver of a multiple speaker system and not to the whole speaker system as might a speaker.

Low-Pass Filter – A circuit that allows low frequencies to pass but rolls off the high frequencies.  Typically used with subwoofers to only allow the low frequencies to be played through that channel.

Mid-bass – Mid frequency bass, usually frequencies just above the sub-bass range, from around 100 – 400 Hz.  A midbass speaker is one that is designated to play those frequencies by using a bandpass filter.

Midrange – A speaker used to reproduce the middle range of frequencies below a tweeter and above a subwoofer.

Motor StructureThe part of loudspeaker comprising the magnet, pole piece, back plate and top plate.

MOSFET – Metal Oxide Semiconductor Field Effect Transistors.  Used in most modern, quality car audio amplifiers in the power supply (and sometimes in the output stage). MOSFET’s run cooler than normal bipolar transistors, and have a faster switching speed.

Octave – An octave is a doubling or halving of frequency.  20 – 40 Hz is up an octave, 80 – 40 Hz is down an octave.

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.

Out of Phase – Term describing when two of more speakers are not in phase with each other.  In a dual subwoofer enclosure, when one woofer is wire in phase and the other woofer is wired out of phase (reverse polarity), they will cancel each other out and the bass response will be very thin.

Output – The sound level produced by a loudspeaker.

Parallel Circuit A circuit configuration in which the same voltage is applied to all components, with current divided among the components according to their respective resistances or impedances.  Example: All positive leads of two or more speakers connected together and all negative leads connected together.

Phase The relative position of two sound waves with respect to each other.

Polarity– The electrical quality of having two opposite poles, one positive and one negative.  Polarity determines the direction in which a current tends to flow.

Power Handling CapabilityThe maximum amount of power that can be safely accommodated without damage in a speaker system.  This will vary depending on frequency and length of time the signal is applied.

Pre-amplifier – A device that takes the signal from the head unit, processes it, and passes it to the amplifier.  The pre-amp may have a number of controls such as an equalizer, crossover, line drivers, time alignment, etc.  The signal processing section of a car audio amplifier can be classified as a pre-amp.

Q or Quality Factor – Is a measure of damping or quality of speaker output.  Most speaker systems have a Q of 0.5 to 2.0.  Lower Q means a smother response but a higher tuning frequency.  The perfect sealed subwoofer enclosure is typically defined by a Q of 0.707

Relay (SPDT) (Single Pole Double Throw Relay) an electromagnetic switch, consist of a coil (terminals 85 & 86), 1 common terminal (30), 1 normally closed terminal (87a), and one normally open terminal (87).

Remote Turn On LeadThe lead from the head unit which supplies a signal (12V+) to the “remote turn on” lead of the amplifier turning the amplifier on when the head unit is turned on, and allowing the amplifier to be mounted in a location out of reach of the user.  This is NOT the amplifier’s main source of power.

Resistance (Re) – In electrical or electronic circuits, a characteristic of a material that opposes the flow of electrons.  Speakers have resistance that opposes current.

Resonant Frequency – The frequency at which an object becomes unstable and starts to vibrate.  A stretched piano string vibrates at its natural resonant frequency when struck.

RMS (root-mean-square) – The square root of the mean of the sum of the squares.  Commonly used as the effective value of measuring a sine waves electrical power.  A standard in amplifier power measurements.

Roll-off (cut-off) – The attenuation that occurs at the lower or upper frequency range of a driver, network, or system.  The roll-off frequency is usually defined as the frequency where response is reduced by -3 dB.

Sealed Enclosure – An air tight enclosure that completely isolates the back wave of a speaker.  Very tight, defined sound (with Qtc = 0.707) with very good transient response and power handling.

Sensitivity – A measurement of how much power is required for a loudspeaker to achieve a certain output level.  The general standard used is on-axis SPL (Sound Pressure Level) at 1 watt input, 1 meter distance.

Separates– A speaker system with more than one type of driver. The most common type of separates system is a set containing two high frequency drivers (tweeters), two lower frequency drivers (mids or woofers), and two crossover networks (filters).

Series Circuit– A circuit configuration in which a single current path is arranged among all components.  Connecting the positive speaker output of an amplifier channel to the positive terminal of speaker # 1, connecting the negative terminal of # 1 to the positive terminal of speaker # 2, and the negative terminal of # 2 to the negative output of the same amplifier channel is a series connection.

Signal-to-noise (SN) Ratio – The range or distance between the noise floor (the noise level of the equipment itself) and the music signal, usually measured in decibels.

Slope– The rate of boost or attenuation expressed in decibels of change per octave.

Sound Pressure Level (SPL) – Given in decibels (dB) is an expression of loudness or volume.

Soundstage – A listening term that refers to the placement of a stereo image in a fashion that replicates the original performance.  A realistic soundstage has proportional width, depth and height.

SpeakerA transducer which converts electrical energy into acoustical energy (sound).

Spider – The flexible material that supports the former, voice coil, and inside portion of the cone within the speaker frame.  The spider is a major part of the suspension system of a speaker and helps keep the driver linear.

Standing Wave – A buildup of vibration or interference at a certain frequency that develops when two sound waves of the same frequency cross each other while traveling in opposite directions.  The location and severity of a standing wave is dependant on the size and dimensions of a room, vehicle, or speaker enclosure.

Subsonic Filter – A high pass filter designed to remove extremely low frequencies (25Hz or lower) from the audio signal.  Useful for vented subwoofer enclosure designs.

Subwoofer – A speaker designed exclusively for low-frequency reproduction.

Surround – The outer suspension of a speaker cone that works with the spider to control the speakers’ linear movement.

Thiele/Small Parameters – The numbers that specify the behavior of a speaker mechanically and electrically, as defined and analyzed by two engineers, Neville Thiele and Richard Small.

Total Harmonic Distortion (THD) – Refers to the harmonics or distortion that an audio device adds to the original signal.  Accurate reproduction of any audio signal requires a low THD.

TransducerA device used to convert energy from one form to another. Acoustical to electrical (microphone), electrical to acoustical (speaker), and electrical to mechanical (bass shaker) are three examples of transducers.

Tweeter – A speaker used to reproduce the higher range of frequencies.

Vb – The total box volume, usually in cubic feet.

Voice coil – The wire wound around the speaker former.  The former is mechanically connected to the speaker cone and causes the cone to move in response to the audio current in the voice coil.

Volt (E) – The unit of measurement used to measure how much “pressure” is used to force electricity through a circuit.

Wattage – Is the unit of power used to rate the output of audio amplifiers.

Woofer– A loudspeaker made to reproduce the lower range of the audio spectrum (bass), in a 2-way or more complex speaker system.