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What basics should I know about pick ups? - Nov 2002
Lower cost & better capability of acoustic amplification has driven widespread acceptance of pickups on acoustic instruments--even among players who wouldn’t have considered “plugging in” before. While ‘perfect’ acoustic amplification is not attainable, affordable, good-quality sound now is–especially with preamps to boost signal & equalizers to balance tone. The following overview discusses pickup types, assets & liabilities, installation & cost.
Magnetic pickups convert string vibration into electric signal through magnetic interaction between a string, a magnet & a coil of wire around the magnet. Steel strings alter the magnetic fields of magnets in pickups; the magnetic fields’ fluctuations induce electron motion in wire coiled around the magnets; the moving electrons are electrical current. Processed by an amplifier, the current makes a speaker vibrate at the same frequencies as the strings’. Magnetic pickups are common on guitars, (the instrument must have steel strings to drive magnetic pickups). Magnetic pickups are relatively resistant to feedback, & easy for players to install. Their sound is warm, though somewhat reminiscent of electric guitars. Dean Markley, Fishman & Shadow offer magnetic acoustic pickups.
Piezo pickups use compression of piezoelectric material to create electric current. When the vibration of a string or instrument soundboard compresses piezoelectric material in contact with it, the compression causes the piezo to emit a small electrical. The signal frequencies match the frequencies of the original vibration. Mounted in/under the bridge or on the soundboard, piezos are available for most instrument families. They’re consistent & resistant to feedback, but sound somewhat ‘quacky.’ Therefore, piezos almost always require additional signal processing to make them sound truly acoustic. Installation generally requires a qualified technician. Fishman, L. R. Baggs, Trance & McIntyre offer piezos.
Microphone pickups are tiny microphones optimized to the frequencies of a particular instrument. Most mic pickups are ‘condenser’ mics that use capacitors (instead of magnets) to convert vibration into electrical signal. A capacitor has two parallel conductive plates with a gap between them. In a condenser mic, one plate moves with a thin diaphragm that responds to air pressure waves from the soundboard. As the distance between the plates changes, the capacitor creates a signal that pulses at the same frequencies as the pressure waves that move the diaphragm. Mic pickups are available for all instrument families, & have very good acoustic sound. However, mic pickups sometimes have a slight ‘hollowness’ to their sound & are quite susceptible to feedback; both issues require additional signal processing. Installation generally requires a qualified technician. Fishman, Seymore Duncan, GHS & L. R. Baggs offer mic pickups.
What can I do?
Cost - good-quality acoustic pickups cost $100 to $200 (audiophile level pickups reach $500). Pickups under $100 are available, but their sound quality is marginal. Pickup installation costs $50 to $150, depending on type of pickup & the installer’s hourly rate. A good quality equalizer/blender/preamp (to tailor the sound that a pickup produces) costs $100 to $350, depending on brand & sophistication. For MOST players’ needs, $300 to $350 will buy a nice-sounding, fully installed acoustic pickup system with an EQ.
(added 9/2/15: This article, now dated, has some obsolete information. Since this article appered, manufacturers changed, added, eliminated and refined their offerings. For example, the article doesn't fully discuss the differences between passive and active systems (those that do not have an external power source to preamplify and those that do) and, K&K, unknown in 2002, now offers wonderful passive oickups that have a signal that is hotter than some of the older active systems and still sound more natural than active pickups - best of all, they do not require a battery inside of your instrument. There are many other examples of changes that have happened over 13 years. As time passes, new technologies and manufacturers will continue to emerge, making today's info obsolete as well. While this article still captures the basics of instrument amplification, calling to learn what's new is a fine idea.)