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Thiele / Small (T/S) Speaker Parameters


Thiele / Small (T/S) Speaker Parameters

This is a short definition list of the Thiele / Small (T/S) speaker parameters. These are electromechanical parameters that can be used to define how a loudspeaker driver performs. They are named after A. N. Thiele and Richard H. Small who pioneered this line of analysis for loudspeakers.

  • D - Effective diameter of driver [m].
  • Sd - Effective piston radiating area of driver [m^2].
  • Xmax - Maximum peak linear excursion of driver [mm].
  • Re - DC resistance of voice coil [ohms].
  • Rg - Amplifier source resistance (includes leads, crossover ...) [ohms].
  • Le - Inductance of voice coil [H].
  • Fs - Driver free air resonance [Hz]. Point at which driver impedance is maximum.
  • Fc - System resonance [Hz] (typically for sealed box systems).
  • Fb - Enclosure resonance [Hz] (typically for reflex systems).
  • F3 - -3 dB cutoff frequency [Hz].
  • Vas - 'Equivalent volume of compliance' [L], measure of the free air 'stiffness' of the suspension. It represents the volume of air that has the same stiffness as the driver's suspension when acted on by a piston of the same area (Sd) as the cone. A larger values mean lower stiffness, and generally require larger enclosures.
  • Vd - Maximum linear volume of displacement of the driver (Vd = Sd Xmax) [m^3].
  • Qms - Q of driver at resonance (Fs), due to mechanical losses [dimensionless].
  • Qes - Q of driver at resonance (Fs), due to electrical losses [dimensionless].
  • Qts - Q of driver at resonance (Fs), due to all losses [dimensionless].
  • Qmc - Q of system at resonance (Fc), due to mechanical losses [dimensionless].
  • Qec - Q of system at resonance (Fc), due to electrical losses [dimensionless].
  • Qtc - Q of system at resonance (Fc), due to all losses [dimensionless].
  • Ql - Q of system at Fb, due to leakage losses [dimensionless].
  • Qa - Q of system at Fb, due to absorption losses [dimensionless].
  • Qp - Q of system at Fb, due to port losses (turbulence, viscosity ...) [dimensionless].
  • n0 (eta sub zero)- Reference efficiency of the system [dimensionless], usually expressed as a percentage.
  • Cms - Mechanical compliance (reciprocal of stiffness) of driver [m/N].
  • Mms - Effective mechanical mass (including air load) of driver [mg]
  • Rms - Mechanical losses of driver [kg/s]
  • Cas - Acoustic equivalent of Cms.
  • Mas - Acoustic equivalent of Mms.
  • Ras - Acoustic equivalent of Rms.
  • Cmes - Electrical capacitive equivalent of Mms [F].
  • Lces - Electrical inductive equivalent of Cms [H].
  • Res - Electrical resistive equivalent of Rms [ohms].
  • B - Magnetic flux density in gap [T].
  • l - Length of wire immersed in magnetic field [m].
  • Bl - Electro-magnetic force factor [Tm].
  • Pa - Music power handling capacity of the driver [w].
  • Pe - Thermal power handling capacity of the driver [w].
  • c - Propagation velocity of sound [~342 m/s].
  • p (rho) - Density of air [~1.18 kg/m^3].

Measuring Thiele / Small (T/S) Speaker Parameters

There are many methods to measure the Thiele / Small (T/S) speaker parameters. Most of them are very tedious and require specialized test equipment. For the speaker DIYer, the Dayton Audio Test System (DATS) is quick, accurate and relatively inexpensive. We use the DATS for our loudspeaker projects.