Doc Loco a écrit :
Bon, une précision quand même : le micro d'une guitare électrique ne fonctionne pas en "attirant" la corde comme je l'ai lu à plusieurs reprises ici!
L'aimant du micro génère un champ magnétique autour de lui; tout objet métallique (une corde ici) qui vibre dans ce champ magnétique engendre une modification du champ magnétique et cette modification de champ entraîne un courant dans la bobine qui entoure l'aimant.
L'attirance de l'aimant n'y est pour rien!
Citation:
There are two basic pickup types, magnetic pickups and piezoelectric pickups. The latter type work with all kinds of strings (steel, nylon, or gut).
Magnetic pickups work only with steel strings, and consist of magnets and coils. Singlecoil pickups are sensitive to magnetic fields generated by transformers, fluorescent lamps, and other sources of interference, and are prone to pick up hum and noise from these sources. Dual coil or "humbucking" pickups use two specially configured coils to minimize this interference. Because these coils are electrically out of phase, common-mode signals (i.e. signals such as hum that radiate into both coils with equal amplitude) cancel each other.
The arrangement of the magnets is different for different pickups. Some types have rod or bar magnets inserted directly in the coils, while others have magnets below the coils, and cores of soft iron in the coils. In many cases these cores are screws, so level differences between strings can be evened out by screwing the core further in or out. Some pickups have a metal cover for shielding and protection of the coils, others have a plastic cover that does not shield against electromagnetic interference, and still others have only isolating tape for protecting the wire.
The magnetic field lines flow through the coil(s) and a short section of the strings. With the strings at rest, the magnetic flux through the coil(s) is constant. Pluck a string and the flux changes, which will induce an electric voltage in the coil. A vibrating string induces an alternating voltage at the frequency of vibration, where the voltage is proportional to the velocity of the strings motion (not its amplitude). Furthermore, the voltage depends on the string's thickness and magnetic permeability, the magnetic field, and the distance between the magnetic pole and the string.
