Qes – Electrical Quality Factor
Qes represents the electrical damping of a driver at its resonant frequency (Fs). It describes how efficiently the voice coil and magnet system control cone movement, with lower values indicating stronger motor control and higher values indicating weaker electrical damping.
How Qes Affects Speaker Performance
- Low Qes (< 0.3) → Strong motor, tight control, high efficiency. Ideal for horn-loaded and high-SPL designs. The motor force is high, sufficient to overcome resistance from air inside the cabinet..
- Medium Qes (0.3 – 0.6) → Balanced damping, suitable for bass reflex (ported) enclosures.
- High Qes (> 0.6) → When the motor force is lower, the driver depends more on its suspension (spider & surround) to return the cone to its neutral position. In a small cabinet, the trapped air acts like an additional spring, increasing resistance to cone movement. A larger cabinet provides less air resistance, allowing the cone to move more freely and extend bass response.
Qes and Its Relationship to Other T/S Parameters
Qes is directly linked to several key Thiele-Small parameters:
- Qts (Total Quality Factor) is calculated from Qes and Qms (mechanical damping)
- Efficiency (η₀) is influenced by Qes—lower Qes generally leads to higher efficiency.
- Enclosure Suitability: A high Qes driver may work better in large cabinets, while a low Qes driver is usually more efficient and can be used in compact, high-output designs.