BL: (measured in Tesla meters) The product of the driver’s gap flux density and the length of the voice coil conductor in the gap.
Decibel (dB): The basic unit of measurement in electronic and acoustic work. It is a logarithmic scale to express the difference between two values. For simplicity, it can be regarded as a measure of relative loudness; for example, in frequency response measurements.
DC Resistance (Re): (measured in Ohms) The actual DC resistance of a speaker’s voice coil as measured with a standard volt/ohm meter. The reading will be lower than the speaker’s nominal impedance. A 4 ohm speaker will typically measure at 3.2 ohms, while an 8 ohm speaker will be about 6.4 ohms. Measuring resistance can be helpful when you are not sure of the speaker’s impedance.
Damping Factor: The ability of an amplifier to control the load without overhang. This applies to how tight the bass is. Usually the higher the number, the better, although it is debatable if anything over 50 is audible. Damping factor is calculated by dividing the load (speaker) impedance by the output impedance of the amplifier. Thus, a given amplifier’s damping factor will decrease as the speaker’s impedance decreases. This means an amp running at 4 ohms will provide tighter bass than at 2 ohms.
Effective Piston Area (Sd): (measured in square inches or meters) The active radiating area of a speaker cone, including the part of the surround which moves to produce acoustic output.
Fb: (measured in Hz) The resonance frequency of the air in a port and the stiffness of the air in a ported system. Also known as the tuning frequency of a vented enclosure.
Fs or Fo: (measured in Hz) The frequency at which a speaker naturally resonates in free air.
F3: (measured in Hz) The frequency at which the acoustic power output from a system has fallen to one-half its reference value. Known as the systems 3dB down point.
Hertz (Hz): The unit of measurement for frequency. 1 Hz is equal to one cycle per second, or the complete cycle of an alternating wave form per second. Impedance: (measured in Ohms) The total opposition to the flow of alternating current in an electrical circuit. The measure of the magnitude of an electrical load when using alternating currents, such as in audio. It describes the combined effect of resistance, capacitance and inductance.
Le: (Measured in millihenries, mH) The electrical inductance of a speaker’s voice coil.
Power Handling: (measured in watts RMS) It is the continuous sine wave power that can be dissipated by the voice coil/magnet assembly without failure. Most speakers fail because the amplifier is driven into hard clipping. Hard clipping produces square wave distortion which can be considered DC. Voice coils are not designed for DC because music is AC. Hard clipping is difficult to identify in subwoofer systems because it is very hard to hear the results of square wave distortion at lower frequencies.
Q: The ratio of reactance to resistance in a series circuit, or the ratio of resistance to reactance in a parallel circuit.
Qes: The Q of a driver at its free air resonance considering only its electrical losses.
Qms: The Q of a driver at its free air resonance considering only its mechanical losses
Qtc: The total Q of a woofer and sealed enclosure at the system’s resonance frequency, considering all resistive losses.
Qts: The total Q of a woofer at Fs, considering all driver resistances.
S Factor: A description of a bandpass enclosure’s frequency response in the pass band. It is a general indicator of the bandwidth.
Sound Pressure Level (SPL): (measured in dB) An acoustic measurement of sound energy. One dB SPL is the smallest audible difference in sound level. Theoretically, 0 dB SPL is the threshold of human hearing at 1 kHz, while 120dB is the threshold of pain.
SPLo: (measured in dB) The speaker’s reference efficiency measured with 1 watt input at a distance of 1 meter from the center of the cone.
Vas: (measured in cubic feet or liters) Volume Acoustic Suspension. It is the volume of air having the same stiffness as the speaker’s suspension.
Vb: (measured in cubic inches, cubic feet or liters) The internal volume of air of a given enclosure.
Vd: The volume of air displaced by the speaker’s cone during an Xmax displacement.
Volume: (Enclosure, Internal - measured in Cubic Inches, Feet or Meters) The result of the product of three linear measurements. Length times width times depth or height, (LXWXH). Volume describes a loudspeaker enclosure size.
Wiring: (Series or Parallel) How two or more speakers are wired together to form a mono system. The wiring of two or more drivers can affect impedance for the whole system. Care must be taken to assure that the resulting impedance does not exceed the amplifier’s requirements.
Xmax: (measured in inches or millimeters) It is the measure of a speaker cone’s maximum excursion in one direction while maintaining a linear behavior.