Humbuckers: Noise Cancellation

A classic trick to eliminate a real-world problem

Toggle between humbucker and single-coil modes to see how the second coil cancels 60Hz electromagnetic interference while preserving the string signal.

The Problem: 60Hz Hum

A single coil pickup is sensitive to any changing magnetic field in its vicinity. This includes both the desirable signal from the vibrating string and undesirable interference from nearby electronics. The most common source of interference is the 60Hz (or 50Hz) hum generated by AC power, which can be heard as a low-frequency buzzing noise when the guitar is near electrical devices or cables.

Sources of 60Hz Interference

  • Power transformers in amplifiers
  • Dimmer switches
  • Computer monitors and power supplies
  • Any device connected to AC mains

AC power runs at 60Hz (50Hz in Europe), creating oscillating magnetic fields that induce voltage in the pickup coil. This is why you might hear a hum when your guitar is near various electrical devices or cables, or if there are many electrical devices in the same room or on the same circuit.

The Solution: Two Coils to Cancel Hum

The humbucker, invented by Seth Lover at Gibson in 1955, uses two coils with a specific arrangement:

Coil 1

  • North pole facing string
  • ↻Clockwise winding

Coil 2

  • South pole facing string
  • ↺Counter-clockwise winding

Opposite windings reverse the polarity of the induced hum, while opposite magnet polarity also reverses the effect of string motion on flux.

Analysis

Recall that a pickup generates voltage based on the rate of change of magnetic flux through the coil:

V = -N × dΦ/dt

For the String Signal:

Coil 1 (N-up): When the string moves toward the pickup, it increases the positive flux through the coil. With north facing up and clockwise winding, this produces a positive voltage.

Coil 2 (S-up): The same string motion now causes the same change in flux, but with a minus sign due to the inversion of the static field. Since the winding is also reversed, the induced voltage is still positive.

Result: Both coils produce the same polarity signal and they ADD

For the 60Hz Hum:

External electromagnetic interference passes through both coils equally. It doesn't care about the magnet polarity because it's not interacting with the magnet at all.

Coil 1: Hum induces a positive voltage (clockwise winding)

Coil 2: Same hum induces a negative voltage (counter-clockwise winding)

Result: Hum signals are opposite polarity and they CANCEL

Coil Splitting

Many guitars with humbuckers include a switch that disconnects one of the coils, converting the humbucker into a single-coil pickup. This is called coil splitting, and it allows players to access the brighter, more articulate tone of a single coil at the cost of reintroducing hum.

Humbucker Mode

  • Full hum cancellation
  • Higher output (both coils)
  • Warmer, fatter tone
  • Less high-frequency content

Split (Single Coil) Mode

  • No hum cancellation
  • Lower output (one coil)
  • Brighter, twangier tone
  • More high-frequency content

Try it: In the simulation above, toggle between humbucker and single-coil modes while watching the waveforms. With the hum level turned up, you'll see the dramatic difference in noise rejection.

Summary

  1. Pickups act as antennas, picking up 60Hz hum from nearby electronics
  2. Humbuckers use two coils with opposite magnet polarity and opposite winding direction
  3. The string signal sees both differences (magnet + winding) and adds constructively
  4. External hum only sees the winding difference and cancels destructively
  5. Coil splitting disables one coil for single-coil tone at the cost of hum rejection