THE GUITAR PICKUP: FORM AND FUNCTION
By Frank Auirgemma
Although the pickup has been with us since 1930s its form, fit and function with regard to successful commercialization and consumer acceptance didn’t take a real hold in the market place until the late 1940s. Leo Fender, a radio repairman by trade, introduced the first commercially successful and well-accepted solid body electric guitar. Solid bodies solved feedback issues that plagued the hollow and semi-hollow jazz guitars as well as Spanish-style guitars adapted to accept them. Although other builders such as Adolph Rickenbacker claim credit as being first into the pickup world, Richenbacker’s application of the ferromagnetic pickup was designed for use in what at the time was called a Hawaiian guitar, not a solid-body electric guitar. Leo Fender really deserves the credit for introducing the solid body electric guitar as we know it today.
More so than any other component, the role of the pickup remains the major contributor to the signature sound of the solid body electric guitar to this day. The solid body electric guitar is truly the most major American contribution to musical instrument history and music in the last 80 years bar none. The sound of the electric guitar is unique and in fact not really a faithful amplified reproduction of an acoustic guitar. Whether we call it blame or innovation, the ferromagnetic pickup has always defined the signature sounds of electric guitars.
Many will argue that the woods, hardware, nut and bridge are contributors to the signature sound of the instrument – and this has some merit. However, keep in mind the nuances of their contributions pale in comparison to the pickup itself because it is the pickup that actually reproduces what effect they have on the guitar’s sound. In fact most of the other considerations defining the sound are mechanical in nature, as the materials affect the harmonic content of the string as they either absorb or reflect vibration energy to or from the plucked or strummed string. To some degree even the pick or the player’s fingers will at times demonstrate a recognizable effect on how the instrument sounds to us.
The ferromagnetic pickup is a relatively crude electronic device in light of the technologies that exist today; however it continues to define the sound we have come to know as electric guitar. Its form and composition is basically universal. The ferromagnetic pickup is primarily constructed from lots of thin wire, a bobbin to wind the wire on and a varying number of magnets. Fundamentally it remains the same beast it was when invented almost 80 years ago.
The function of the ferromagnetic pickup is that of a transducer: it transforms one form of energy to another. Perhaps a good analogy is a microphone, which is also transducer that converts sound pressure waves striking a diaphragm to electrical energy. A ferromagnetic pickup converts vibration – in this case the motion of a string within a magnetic field – to electrical energy.
From a good engineering practice point of view a well-engineered transducer is one that can faithfully provide a highly linear transfer function. Transfer function is just another way of saying a known input will result in a mathematically predictable output over as broad a range as possible. In the case of a ferromagnetic pickup or a microphone, the transfer function will define the amplitude (loudness), pitch (musical note) and tone (harmonic content) for input in one form of energy to output in a different form of energy.
Using the microphone analogy one may ask why a high quality condenser microphone sounds better than a dynamic microphone. Simply stated it is because the condenser microphone’s transducer is designed to be very accurate across a broad range of frequencies and is capable of detecting these frequencies with more precision.
A high quality microphone will minimize the introduction of artifacts in the form of phase relationship anomalies and output amplitude variations while providing the best possible linear transfer function as it converts sound pressure to volts. This is all related to the design requirements defining the nature of microphone construction. Unfortunately (or perhaps fortunately in the case of guitar pickups), the practical, mechanical and electronic realities prevent us from making a pickup of traditional design with a high degree of linearity across the frequency range the instrument is capable of providing to the pickup. These real world limitations define what our ears expect when we listen to an electric guitar.
From a strict engineering perspective as we evaluate the pickup for its accuracy, we should be pretty disappointed with its performance. We are not, however, and more importantly we do not at all care about its technical accuracy. We care only about how it sounds. We certainly wouldn’t use a microphone in the same way when trying to faithfully reproduce what our ears are hearing. From the day of its invention to the present it is exactly these shortcomings that create what we expect to hear from the pickup as it performs its function as related to this instrument we call the electric guitar.
What are the shortcomings of a pickup? From a good practices and engineering point of view the biggest culprits would be limited frequency response, non-linear frequency response, noise artifacts and most importantly lack of isolation when more than one is used. Further evaluation of a guitar pickup system demonstrates the passive volume and tone controls as well as the cable that connects the instrument to the amplifier are serious contributors to deleterious effects on the sonic potential of the pickup.
For the past 50 years pickup manufacturers have worked within the same guidelines to improve the pickup. Have pickups actually improved? That is a matter of semantics as they have provided a virtual cornucopia of iterations that alters the transfer function to some extent. Are these improvements? Inasmuch as they provide enhancements with regard to reduced hum, altered frequency response and greater output, yes they are improvements. The problem lies in improving any one of the above compromises any or all of the others. Dramatic improvement of the pickup from a purely good engineering practice point of view will undoubtedly and profoundly change the sonic performance of the pickup resulting in what more than likely many may consider an alien listening experience. This might actually be a bad idea, as the signature sounds of America’s major contribution to the world of musical instruments should be preserved largely as it is, but remain open to further improvements.
Now one may ask is there anything to be done to push forward the science and the art of ferromagnetic pickups? Can these things really be improved any more than they have while preserving our sonic expectations? If so, will the differences be profound enough to make a difference? The answers to these questions are unequivocally “YES”. As a matter of fact, some advances addressing this veritable “Catch 22” are available now and others are emerging.
Improvements in pickup design can indeed be made as long as builders keep in mind the design requirement is dramatic sonic improvement without affecting the listener’s overall tonal expectations. I’ll address this in my next installment.