ThieleSmall

Thiele–Small parameters are a set of electromechanical properties that describe a loudspeaker driver’s behavior under small-signal conditions. Named after A. Neville Thiele and Richard H. Small, the parameters quantify how the moving system, the suspension, and the acoustic load interact with the electrical voice coil to determine impedance, resonance, and output. They are used to model a driver’s performance and to predict how it will behave in different enclosure configurations.

Core parameters commonly cited include: Re, the DC resistance of the voice coil; Le, the voice-coil inductance; Sd, the effective radiating area; Vas, the equivalent air volume that would produce the same suspension compliance; Cms, the mechanical compliance of the suspension; Mms, the moving mass; Bl, the magnetic flux product (motor strength); Fs, the free-air resonance frequency; Qts, the total Q at resonance; Qes, the electrical Q at resonance; Qms, the mechanical Q at resonance; and Rms, the mechanical resistance. Together these values describe the motor, suspension, and acoustic loading of the driver, and they form the basis for predicting impedance, efficiency, and enclosure interaction.

Measurement and use: Thiele–Small parameters are typically obtained from impedance measurements and sometimes mechanical tests with the driver mounted in a test enclosure. They enable calculations and simulations that guide enclosure design, such as sealed or ported boxes, and help determine suitable box volume, tuning frequency, and expected low-frequency response. Limitations include their validity only for small excursions and linear operation; they assume consistent mounting, temperature, and air load, and they do not capture nonlinear behavior or large-signal effects. The Thiele–Small framework remains a foundational tool in loudspeaker design and specification.