Qts

Qts is a parameter used in loudspeaker engineering to describe the overall damping of a driver when it is driven electrically. It is the total quality factor of the driver, combining mechanical and electrical losses. The standard relationship is Qts = Qms × Qes / (Qms + Qes), which can also be written as 1/Qts = 1/Qms + 1/Qes. Qms is the mechanical quality factor of the suspension and the mechanical system, reflecting how the cone and surround dissipate energy. Qes is the electrical quality factor tied to the voice coil resistance and the motor assembly, reflecting how the electrical circuit damps the motion.

Qts influences the driver’s resonance behavior, the shape of the impedance near the free-air resonant frequency, and the potential bass extension. A lower Qts indicates stronger damping and a smoother, more controlled response, while a higher Qts indicates less damping and a more pronounced resonance, which can affect bass linearity and efficiency.

Enclosure considerations: Qts helps determine suitable enclosure types for a driver. In general, drivers with low Qts (roughly below 0.4) are common in sealed enclosures for tight bass, whereas higher Qts drivers (around 0.4–0.6 or higher) are often used in vented (bass-reflex) designs to achieve deeper bass with practical box sizes. However, exact outcomes depend on other Thiele–Small parameters such as Vas, Fs, and the desired system response.

Qts is one parameter among many in speaker design and is used alongside Fs, Vas, Qes, and Qms to predict performance and guide enclosure decisions.