BL factor

The BL factor (drive factor), given in Tm (tesla-metres), gives the strength of the motor structure applied to the voice coil. A high drive factor is a precondition for high sensitivity and, at the same time, damps the speaker's self-resonance. If the BL factor is too high, however, bass reproduction will be poor. Where it is too high, the self-resonance will be exaggerated and the pulse response will be poor at low frequencies.