As rock music developed and grew in popularity, amplifiers became larger and featured higher wattage, and the music became louder and more powerful sounding as a result. This led to a call for a more versatile pickup that could split coils through a push/pull knob and prevent microphonic feedback from occurring when the volume was turned up to maximum levels. Gibson answered this call with the introduction of the revolutionary 490T and 490R pickups ("T" for treble and "R" for rhythm), which have the traditional characteristics of the original Patent Applied For pickups, but with two key modifications. First, a four-conductor wiring scheme allows the 490s to be connected to any push/pull knob, which lets players split the coils and increase versatility. Gibson also introduced wax potting, which does away with any air space, minimizing microphonic feedback. The 490R is a humbucker with the tonal characteristics of an original Patent Applied For, with a slight increase in upper midrange response. The 490T bridge pickup is calibrated to match the 490R, with pole pieces aligned a little further apart to accommodate the spacing of the strings at the bridge, which is different than the spacing of the strings at the neck.