When a current-carrying conductor passes through a magnetic field, it receives an electromotive force whose direction conforms to Fleming's left-hand rule. The force, current, and magnetic field are perpendicular to each other, and the force is proportional to the current, wire length, and magnetic flux density. When the voice coil inputs an alternating audio current, the voice coil is subjected to an alternating driving force to produce alternating motion, which drives the paper cone to vibrate and repeatedly push the air to produce sound.
The force that makes the diaphragm of the electrodynamic speaker vibrate is the force of the magnetic field on the current-carrying conductor. This effect is called the force effect of the electrodynamic transducer, and its magnitude is specified by the following formula:
F=B L i
In the formula: B is the magnetic induction density (intensity) in the magnetic gap, and its unit is N/(A.m)<Newton/(Ampere. Meter)> also known as Tesla (T)
L is the length of the voice coil wire, unit: meter
i is the current flowing through the voice coil, unit: ampere
F is the force of the magnetic field on the voice coil, unit: Newton
However, when the energized voice coil moves under force, it will cut the lines of magnetic force in the magnetic gap to generate an induced electromotive force in the voice coil. This effect is called the electrical effect of an electrodynamic transducer. The magnitude of the induced electromotive force is :
е=Вiν
Where: v is the vibration speed of the voice coil, and its unit is: m/s
е is the induced electromotive force in the voice coil, the unit is: volt
The force effect and the electric effect of the electrodynamic speaker exist at the same time and go together.
