Exploring Common DIY Terminology - Fs

Fs (Thiele/Small Parameter)

The Thiele/Small parameter "Fs" refers to the resonant frequency of the loudspeaker driver. Fs stands for "Free-air resonance" or "System resonance." It is a crucial parameter that characterizes the natural frequency at which a driver's diaphragm vibrates with maximum efficiency when operating in free air, without any enclosure or load. This resonant frequency is determined by the combined effects of the mass of the driver's diaphragm (including the cone and voice coil assembly) and the compliance of the driver's suspension system (surround and spider). It represents the point at which the driver's mechanical and electrical properties are balanced, resulting in maximum efficiency for converting electrical power into sound.

When a driver operates below its resonant frequency, it behaves as a low-pass filter, gradually attenuating higher frequencies. Above the resonant frequency, it behaves as a high-pass filter, rolling off lower frequencies. The frequency response of a driver is typically most extended and flat around its Fs.

Fs is measured in Hertz (Hz) and can vary significantly depending on the size, mass, and compliance of the driver's diaphragm, as well as the design of the suspension system. It is an important parameter to consider when designing loudspeaker systems, as it helps determine the appropriate crossover frequency and enclosure tuning for optimal performance and integration with other drivers in a multi-way loudspeaker system.



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