Glossary

BL
The cross product of the magnetic gauss in the gap ‘B’ with the effective conductor length ‘L’. BL is measured in Tesla meters or Newtons per Ampere (same units)
Cab
Compliance of the driver inside the box.
Cas
Compliance (1/stiffness) of the driver’s suspension system measured in (same as Cms).
Cms
Compliance (1/stiffness) of the driver’s suspension system (same as Cas).
Fc
Resonance frequency of the driver in a closed box system.
Fs
Resonance frequency of the driver in free air.
Lp
Inductance in a parallel circuit model with the Rp resistor
Ls
Inductance in a series circuit model with the Rp resistor
Q
Ratio of reactance to resistance or vice versa. This terms can apply to mechanical, electrical or even pneumatics’s models. Its often used to describe drivers (Qts), filters or entire systems (Qb).
Qes
The Q of the driver at Fs as a function of electromotive damping factor.
Qms
The Q of the driver at Fs as a function of the mechanical damping factor.
Qts
The combine factor of Qes and Qms of the driver.
Rp
Resistor used in the inductance circuit model with either Ls or Lp
Sd
The effective surface area of the driver’s cone.
Vab
The volume of air which has the same compliance as driver inside an enclosure.
Vas
The volume of air which has the same compliance as the drivers suspension in free air.
Vb
Net volume of an enclosure.
Vd
Maximum linear displacement that the driver can do.
BL²/Re
BL²/Re is a composite terms used to define the raw efficiency of the motor relative to a given power level. BL is the actual cross product of the magnet field “B” with the conductor length “L”. It is not a scalar, but rather a vector. Combine this vector with the current I and you’ll get exactly the force (up or down according to the DC or AC input). But with the way amplifiers are designed, the current I of the speaker is never constant, only the voltage is. The BL squared divided by the resistance of the voice coil Re yields a generic force factor in newtons squared per watt. This number is relative for all speakers and the higher the number the more force a motor can invoke on a cone with the same input power.It’s important to distinguish that BL and Re are related much like inductance and Re are. For example, 32Tm over 8 ohms is identical to 16Tm over 2 ohms, namely 128 N²/W. All other things equal (moving mass and cone size in particular), A higher BL²/Re will increase the sensitivity of the driver which is a generally a very good thing.