How to Choose Guitar Pickups - A Parametric Approach

As one gains experience playing guitar, the desire to improve will eventually extend beyond practicing and will lead to exploring better equipment. Guitar pickups are an important component in the guitar equipment ensemble, but are not widely understood, even among experienced guitar players. This blog will serve to briefly explain what guitar pickups are, why they matter, and how an enthusiast of any guitar skill level can use this information, and their familiarity with electronics and basic electrical theory, to make an informed and parametric decision when purchasing them.

1. Understand What Pickups Are

Anyone who is relatively practiced knows, or thinks they know, what a guitar pickup is. It is a safe assumption that most only have an elementary understanding of what a pickup is, meaning with respect to the guitar, e.g. what it looks like, where they are mounted on a guitar, and their general function.

While having only a basic understanding of what pickup is will not prevent you from improving your skills, it will definitely limit your ability to make an informed decision when purchasing new pickups.

Guitar pickups are transducers which convert the vibrations of guitar strings into electrical signal. This conversion is done by a coil and magnet. 

The magnet serves to magnetize the guitar string. The guitar string thus acts as a vibrating magnet once it is struck. Each oscillating movement of the guitar string will cause and correspond to a change in the magnetic flux of the coil. Changes in the magnetic flux of the coil will induce a voltage, of varying degree, in the coil. If plotted, the graph of the voltage induced would be a sinusoidal wave, moving up and down just as the guitar string does when it vibrates. The voltage is transmitted as an electrical signal by wires connected to the coil in the pickup, which can then be fed through an audio cable and into an amplifier. In summary, the vibration of the guitar string is converted into a voltage that "vibrates" (oscillates) just as the string does.

2. Understand Why Choosing the Right Pickup Matters

Understanding why choosing the right pickup matters is what will take you from this... to this.

Jimi Hendrix, famed guitar player who utilized numerous
 innovative techniques to transmit sound from his guitar

Electrically, guitar pickups act as a second order low-pass filter circuit, which can be modeled in a circuit diagram as an "RLC" circuit. A circuit consisting of a resistor, an inductor, and a capacitor, where the input voltage is the voltage translated from the oscillating guitar string to the coil.

Low-pass filter circuits function as their name suggests, a cutoff frequency is designed into the circuit, and any frequency lower than the cutoff frequency is allowed to pass through, hence, low-pass. Frequencies higher than the cutoff frequency are filtered out.

At a frequency just below the cutoff frequency, the virtual maximum frequency allowed to pass through steadily, there is a peak in the frequency amplitude, meaning signals at this frequency pass through the low-pass filter at maximum strength. This ideal frequency is referred to as the resonant frequency of the pickup and is a defining parameter in pickup choice. The resonant frequency of most pickups is in the range of 2,000 - 5,000 Hz. A resonant frequency between 2,000 - 3,000 Hz will produce the most generally appealing sound.

The resonant frequency output of a pickup is primarily a function of three variables:

1. The pickup's inductance and capacitance
2. The capacitance of the guitar cable being used
3. The input impedance of the amp being used

These variables in the resonant frequency must be deliberately chosen in order to get the desired resonant frequency in the range of 2,000 - 3,000 Hz. Only certain combinations of these three variables will yield the optimal resonant frequency. Deviation outside of the optimal value in each of the three variables will result in undesired resonant frequency and thus a less than ideal output sound.

While optimization techniques that involve the the 2nd and 3rd variables are outside the scope of this blog, illustrating that pickups are a fundamental part of the resonant frequency equation serves to explain why choosing the right pick up is important. Once the ideal frequency range is achieved, the pickup's inductance has further implications on sound quality and tone, which make it the driving parameter in choosing a pickup.


3. Leverage Your Understanding to Make an Informed Purchasing Decision

Once you are familiar with the desired parameters in a guitar pickup, you are equipped to make an informed purchasing decision. To reiterate, the goal is to find a pickup that, in conjunction with your guitar cable and amp, will produce a resonant frequency in the 2,000 - 3,000 Hz frequency and that is most suited to your tastes. For the purpose of the technical scope of this blog, it will be assumed that the cable and amp combination are already intelligently chosen. The objective of the consumer is to now purchase a pickup based on the inductance value that fits the desired sound. The consumer should then familiarize themselves with the sounds produced by pickups of different inductance values in order to develop an understanding of the affect of inductance value on sound output. Pickup manufacturers typically publish audio samples of their products, these samples are a great resource for familiarizing oneself with different pickup sounds.

The primary goal of the informed consumer is to examine how choosing a pickup, based on a measurable and quantifiable parameter, can positively benefit the output sound of the guitar. The spec of interest, when it comes to purchasing a pickup, is primarily the pickup's inductance. In the abstracted sense, the inductance is a measure of the electrical "size" of the coil. In reality, different inductance values generate different resonant frequencies and thus the inductance values provide an easily measurable characteristic of the pickup that can be used to drive purchasing decisions.

The smaller the inductance value of the pickup, the more treble will be produced in the sound output. Whereas, higher inductance values correlate to more midrange and bass. These two boundary conditions, high and low inductance, allow for a spectrum of sound quality to be developed on a scale of inductance values. To assign some numbers and familiar guitars to these inductance values, a Fender Stratocaster comes stock with pickups with 2.2 H of inductance, whereas a Fender Precision Bass ("P-Bass") has pickups with 6.0 H of inductance.

The inductance values for pickups can be found in their spec sheet. A parametric approach to choosing a pickup will free you from pick up manufacturer's marketing tactics of subjectively describing the sound output and quality of their product, allowing you to base your purchasing decision on a measurable parameter of sound output and quality, the inductance.



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