Qms – Mechanical Quality Factor

Qms represents the mechanical damping of a speaker driver, determined by the losses in the suspension system (spider & surround). It indicates how well the driver’s mechanical components control cone movement at resonant frequency (Fs).

What Qms Tells Us About a Driver

• High Qms (> 5) → Low mechanical losses, meaning the cone moves more freely with minimal damping from the suspension.
• Low Qms (< 3) → Higher mechanical losses, where the suspension provides more damping and absorbs energy.

How Qms Affects Speaker Design

Qms works alongside Qes (electrical damping) to determine the total damping (Qts) of a driver.

A high Qms driver has minimal mechanical resistance, allowing for greater resonance, but relies more on electrical damping (Qes) for control. A low Qms driver has more built-in damping from the suspension, reducing unwanted resonance but also limiting efficiency.

While Qms alone doesn’t dictate enclosure suitability, it plays a role in how much influence the motor vs. suspension has on cone movement, helping in overall system tuning.