6 Loudspeaker cabinets

6.13 Thiele-Small parameters

In the past, two gentlemen, Albert Thiele and Robert Small, have developed a measurement standard for loudspeaker characteristics. The Thiele/Small parameters, T/S parameters in short, are what defines a loudspeaker. These parameters are a list of figures of mechanical and electrical constants:

Description Interpretation
Fs Hz Hz Free air resonance frequency Specifies the frequency at which the driver resonates in free air, floating in an infinite space.
Qms - - Mechanical Q factor These three figures describe how the driver resonates. The bandwidth of the resonance is split into motional resonance (Qms) and electrical resonance (Qes). Their value is combined in Qts. This value is of great importance to cabinet design.
Qes - - Electrical Q factor
Qts - - Total Q factor
Vas ft3 dm3 Equivalent air volume Specifies the volume of air to have an equivalent suspension to the cone's suspension
Cms in/N mm/N Suspension compliance See 6.1 6.1 Loudspeakers. Specifies the force needed to move the cone assembly a given distance
B T T Magnetic field strength Strength of the magnetic field inside the air gap in Tesla
BL N/A * N/A * Force factor Specifies how much force the voice coil will apply to the cone at a given current
Xmax in mm Maximum linear cone displacement See 6.1 6.1 Loudspeakers
Xdmg in mm Maximum cone displacement before damage occurs See 6.7 6.7 Power handling
η0 dB dB Reference efficiency See 6.10 6.10 Efficiency and sensitivity
Sens dB dB Sensitivity is the measured, real world efficiency See 6.10 6.10 Efficiency and sensitivity
Pth, Pcont W W Thermal power or continuous power See 6.7 6.7 Power handling
Ppeak W W Peak power See 6.7 6.7 Power handling

* Note: this is Newton per Ampère, it doesn't mean "Not Available"

© Joris van den Heuvel 2001-2009