Q: What are “RWRP” pickups and what do they do?
A: “RWRP” is an abbreviation for “reverse-wound, reverse-polarity” and refers to a technique used to build pickups so that they cancel hum. To understand how this works, a quick explanation of how pickups work is in order.
In a magnetic pickup, wire is wound around a fixed magnet and sound is created by a vibrating guitar string being magnetized, inducing an alternating current across the coils of wire. Unfortunately, wire coils are also excellent antennae and sensitive to interference caused by any alternating magnetic fields, i.e., anything using alternating current or plugged in to the wall. The result of this interference is an audible buzz or hum when amplified, becoming increasingly noticeable at higher volume and gain levels.
To counteract this effect, the output of a second magnet with the wire wound in the reverse direction and the magnet’s pole inverted (reversed) is summed to the first magnet. Voltage created by a vibrating string is affected by both winding direction and magnet direction but electromagnetic interference is only sensitive to the direction of the wire wind. The motion of the vibrating string induces voltages across both coils in the same direction while the noise of the interference creates voltages in two opposite directions. When the signals from the two coils are summed, the noise voltages cancel each other (the “hum” is “bucked”) and the vibrating string signal is multiplied; more sound of the string, less sound of the hum.
This is the principle behind the humbucking pickup. In guitars with more than one single-coil pickup, one of the pickups can have wire that is wound in the opposite direction of the other pickups (reverse-wound) and its magnet’s pole inverted (reverse-polarity) so that when two pickups are selected, a humbucking effect is created, canceling noise.
In short, one single-coil pickup is reverse-wound, reverse-polarity (RWRP) in relation to the other pickups in the guitar and when the RWRP pickup is selected in conjunction with one of the other pickups, a hum-canceling effect takes place.