Speaker Term Glossary
A measurement of the motor strength of a speaker driver. Measured in Newtons per Ampere (N/A), Tesla meters Tm, pounds per Ampere (lbs/A) or Tesla feet (T/ft)
The mechanical compliance of a speaker driver's suspension (surround, cone and spider). Measured in inches per pound or millimeters per Newton.
The "piston" diameter of a speaker driver.
The inside diameter of the port tube in a vented cabinet speaker system.
The resonant tuning frequency of a vented speaker cabinet.
The resonant frequency of a sealed speaker cabinet.
The free-air resonant frequency of a passive radiator.
The free-air resonant frequency of a speaker driver. The frequency at which an object tends to vibrate. For example, although a bell can be externally driven to vibrate at different frequencies, it will always naturally tend to vibrate at it's given tuned tone, or resonant frequency.
The point at which the signal strength of a loudspeaker falls 3 decibels below the loudspeaker's rated SPL, as the frequency decreases.
Pronounced "hurts". Unit of measurement for cycles of vibration per second. Also kHz or kilohertz (1000 hertz) and MHz or megahertz (1 million hertz).
Inductance. Usually specified for a voice coil of a speaker driver.
The length or depth of a vented speaker cabinet's vent.
Microfarad (µfd or MFD)
Unit of measure for capacitance. One millionth of a farad.
Unit of measurement for inductance. One one-thousandth of a Henry.
The mechanical mass of a loudspeaker diaphragm assembly including the air load.
The reference efficiency of a loudspeaker with a half-space acoustical load.
Represented by the Greek omega symbol. It is the unit of measurement for resistance and impedance.
The maximum electrical power that a speaker driver can handle before it is damaged, usually when the voice coil burns.
The amplitude difference between the most positive and the most negative excursions of a signal.
The losses or relative damping (ratio of stored to dissipated energy or ratio of reactive to resistive energy) of a system.
The total Q of a loudspeaker's suspension with the load of the rear chamber in a 4th-order bandpass box.
The Q of a sealed (closed) loudspeaker at Fc considering only its electrical (non-mechanical) resistances.
The losses or relative damping (ratio of stored to dissipated energy or ratio of reactive to resistive energy) of a vented loudspeaker at Fs considering only its electrical (non-mechanical) resistances.
The Q of a vented speaker cabinet resulting from all of the box losses (acoustic weaknesses).
The Q of a sealed loudspeaker cabinet at Fc, considering only its mechanical (non-electrical) resistances.
The losses or relative damping (ratio of stored to dissipated energy or ratio of reactive to resistive energy) of a vented loudspeaker cabinet at Fs, considering only its mechanical (non-electrical) resistances.
The Q of a sealed loudspeaker considering both mechanical and electrical resistances.
The losses or relative damping (ratio of stored to dissipated energy or ratio of reactive to resistive energy) of a vented loudspeaker considering both mechanical and electrical resistances.
The DC resistance of a speaker driver's voice coil.
The mechanical resistance of a loudspeaker's suspension losses.
RMS (Root Mean Square)
Technically speaking, RMS=.707 X (peak measured power). Basically it can be considered the "average" operating wattage.
The measured surface area of a speaker's piston.
The reference sensitivity of a loudspeaker measured at one meter as a sound pressure level. It was originally measured while driving a speaker with one watt, but is also measured driving a speaker with a constant 2.83 volts AC.
SPL (Sound Pressure Level)
The measured loudness of a sound. Often measured in decibels (dB) from one meter (1m) away from a speaker driver while it is playing a test tone that is being driven by one watt (1W) of power from the amplifier. (Example: 92 dB 1W/1m) Also measured from a speaker that is being driven with 2.83 volts of audio voltage. (Example: 92 dB 2.83V/1m)
Thiele-Small parameters, a certain collection of loudspeaker specifications named after the scientists who developed them.
The volume of air having the same compliance, or ease of movement, as the suspension (surround, spider, etc.) of a speaker driver, i.e. a driver with a loose suspension will have a higher compliance and low Vas.
The internal volume of a vented speaker cabinet.
The internal volume of a sealed speaker cabinet.
The maximum linear excursion of a loudspeaker voice coil while remaining within the magnetic flux field.
The nominal electromagnetic impedance of a loudspeaker or electronic system.