Microphones & Pickups
This page provides basic information on the three most common sorts of mics or pickups and their applications, with further information on compact pre-amps. It also has basic information on wiring procedures and options for piezo pickups that aren’t pre-wired. If you’re not already knowledgeable, we encourage you to read the relevent portions of this page before buying one of our pickups – it’ll help you to know what the options are and to make a good buying decision. For really good, complete information, purchase our book Getting a Bigger Sound: Pickups and Microphones for your Musical Instrument, which treats this topic in far greater depth.
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Background and Information
Microphones and pickups are devices that convert the vibrations from a musical instrument or other sounding object into an electrical signal that can be sent to an amplifier and speaker. In traditional microphones, that original vibration is a sound in the air. Other sorts of pickups may not be responsive to vibrations in the air, but rather to vibrations in the instrument itself – in a string, for instance, or a soundboard.
In theory there are many ways to approach the task of converting a vibration to an electrical signal. But for practical purposes, there are three systems currently in widespread use. They are:
- Air microphones, which respond to sound vibrations in the air
- Contact pickups, which are attached to solid vibrating objects and respond directly to their movement
- Magnetic pickups, which are placed near vibrating bodies of ferrous metals, such as steel strings, and respond to the vibrator’s movement across a magnetic field.
Since air microphones respond to the same vibrations in the air that the ears do, a good air microphone will usually yield the most accurate and natural-sounding reproduction of an acoustic instrument’s sound as the ear hears it. Air microphones work with any audible sound source. The greatest disadvantage of air microphones is that they are very much prone to feed back (starting to howl uncontrollably when the volume is turned up past a certain level, as the sound from the speakers cycles back into the mic). Another disadvantage is that they aren’t selective — they pick up not only the sound of the instrument, but any other sound in the vicinity. Sometimes air microphones can be built into a musical instrument, but more typically they are placed on a separate stand in front of the instrument.
Where to get air mics: Air mics, in countless makes and models, are available in music and audio stores of the online, catalog and storefront types. ExMI doesn’t sell them.
These are the sorts of pickups used on electric guitars. More generally, they can be used in any application where the vibrating body is of a ferrous metal (iron or steel). Thus, in addition to the electric guitars and bass guitars on which they’re most often used, they can also work, for example, on kalimbas with steel or iron tines, various sorts of tuning fork instruments, and vibraphone-like instruments with steel bars, as well as zithers and other steel-stringed instruments. What gets amplified with magnetic pickups is not the vibration in the air that the ear would hear without amplification, but a replication of the movement of the string or tine or whatever.
Advantages: While the tone of a magnetic pickup is not a replication of the audible acoustic sound of the instrument, it often is, subjectively speaking, an attractive sound. Feedback problems are minimal, as are problems with unwanted extraneous noise. Given a suitable model of pickup, they are easy and unobtrusive to mount on the instrument.
Disadvantages: They only work with ferrous vibrating bodies. They are prone to humming, with some models being worse in this respect than others. They must be sized and shaped in a way that allows them to be positioned close to all the vibrating bodies. This isn’t a problem for electric guitars, for which many makes of suitably sized and shaped pickups are available, but it is a potential problem in applications like, say , an electrified kalimba, which would call for an extra-long pickup to extend under all the tines. Or an electrified tubulon (that’s a steel conduit marimba), which would call for a small spot pickup under each tube. Such non-standard sized pickups are not normally available. Fortunately, we have those hard-to find pick-up sizes in stock here at Experimental Musical Instruments. For sizes even beyond what we’ve got, you can wire two or more pickups together, or have larger ones custom-built, or you can make them yourself (admittedly, a laborious process when done by hand).
The magnetic pickups we sell come with rudimentary wiring diagrams for either direct connection to a plug or jack, or routing through a volume control on the instrument.
Where to get electromagnetic pickups: There are several options, depending on the size needed.
- To purchase standard-size magnetic pickups (designed for electric guitar or bass – good for applications up to a little over two inches), you can turn to one of the many local or online music stores, or to one of the big discount music merchandisers like Musician’s Friend; or, for best quality and selection, to guitar supply houses like Stewart-MacDonald (http://www.stewmac.com) or Luthiers Mercantile (http://www.lmii.com).
- For spot pickups — that is, small, circular pickups designed to go under one string, one kalimba tine, one tubulon bar, etc. — use our spot pickups.
- For sizes between 2″ and 4″: use one of our 8-inchers (see below) or wire two standard guitar pickups together.
- For sizes between 4″ and 8″: use one of our 8″pickups.
- For larger or other odd sizes, you can 1) wire two or more pickups together, 2) arrange to have pickups custom-built, or 3) custom build for yourself. For custom building, we recommend Lollar Guitars at http://www.lollar.hypermart.net. An excellent source for information on do-it-yourself pickup winding is our book Getting a Bigger Sound: Pickups and Microphones for your Musical Instrument, available through our catalog.
(also known as contact mics and piezo-electric pickups or transducers)
Contact pickups respond to the vibratory movement of whatever body they’ve been attached to. They can be attached to a soundboard, a drumhead, a marimba bar, or, for that matter, a window, a wall or a table. Contact pickups can be attached to the body of an instrument by glue, sticky putties, double-sided sticky tape or various other means. One of the main factors in the quality of the signal you get from a contact pickup is where and how you mount it on the instrument. There’s room for experimentation here, and the contact pickups we sell come with information sheets or booklets giving mounting suggestions for various instruments.
Disadvantages of contact pickups: They are less subject to feedback than air mics, but they aren’t feedback-proof, especially when attached to soundboards. They may produce an exaggerated and disconcerting response to any unintentional knocking or scraping on the body of the instrument. It’s generally assumed that contact pickups cannot be used with wind instruments, although this isn’t entirely true: some types of contact pickups can work some wind instruments. Most important disadvantage: contact pickups often produce an unattractive and unnatural sound, which requires a good deal of tweaking and signal processing to make it more acceptable. However, recent years have seen improvements, and it is possible nowadays to get a very good sound from them.
Where to get contact pickups: Right here at Experimental Musical Instruments, through the online catalog or the print version of our catalog.
More on Contact Pickups
One of the main features of the contact pickups we carry is their versatility. When you look for pickups in the mainstream outlets, you find lots of pickups designed specifically for acoustic guitars. Aside from being limited by their configuration to a single instrument, these generally require some fancy work to install (typically the manufacturers recommend getting a professional guitar repair person to do the installation). For the ExMI Catalog, we wanted pickups that could be used on all sorts of instruments, conventional or exotic, and that are not only easy to put on, but are easy to take off again, put on again, try out on a different instrument, shift to yet another instrument as the need arises, etcetera. Both the K&K Hot Spots and the piezo film pickups we carry can be quickly and easily attached to the body of the instrument using an adhesive such as double sided tape. At the same time, both also are excellent choices for permanent or semi-permanent installations.
As you can surmise from what I’ve just said, in the most basic applications, contact pickups are as simple as can be to install and use: stick the pickup on the instrument, plug in and play. But on the other hand, when it comes to knowing all the ins and outs, and using that knowledge to bring out the best possible sound — well, as the saying goes, you could write a book … and as mentioned above, we have indeed written a book. But in the mean time, some very basic information follows here.
It’s important to recognize that there are limitations in the very nature of the contact pickup idea. The sound of a typical acoustic instrument is a complex and ever-changing blend of many components. To use the most common example, the natural sound of an acoustic guitar incorporates the effect of the soundboard vibrating as a whole, which includes many different sections of the soundboard vibrating quasi-independently, with varying phase, amplitude and frequency relationships. In addition, an essential component of guitar sound is the air resonance coming from the sound-hole. Added to this are the quiet but finely delineated sounds coming directly from the strings themselves. A well placed air microphone will pick up all of this. But a contact pickup will transcribe only the movement of a single point on the sound board — a rather one-dimensional representation of what is in fact a many-dimensional sound-event. In spite of this, you can still manage to get a very good sound from a contact pickup — I’ve heard plenty of good examples myself.
Most contact pickups operate by means of the piezo-electric effect. Piezo-electric materials are materials which produce a tiny change in voltage when flexed or subjected to stress. When the material is attached to a vibrating body, an alternating voltage appears which reflects the vibrating body’s pattern of movement, and this constitutes the signal to be taken from the pickup and sent to an amplifier and speakers. Traditionally, such pickups have been made with thin a layer of piezo crystal bonded to a thin, rigid metal disk. More recently, people have recognized the benefits of piezo films, which take the form of ribbons or sheets of non-rigid polymer material. While rigid piezo pickups often give a rather tinny, scratchy sound, piezo films will usually give a smoother, better-balanced response. There are several reasons for this: one is that they are free of self-resonance. (The bodies of rigid piezos, by contrast, often have inherent acoustic resonances which tend to bias the frequency response.) Another is that piezo films, especially larger ones, can be responsive over a larger surface area, and this also contributes to a response more representative of the vibrating surface as a whole. At its best, a piezo film mounted inside the soundboard of an air-chamber instrument such as a guitar will even be sensitive enough to pick up some of the air resonance that rigid piezos generally miss. We have found that some of the piezo films produce a small hum, even when seemingly well shielded. In the great majority of cases it is so small as to be entirely negligible.
Here at Experimental Musical Instruments we carry three types of contact pickups. One comes from K&K Sound Systems, makers of the most affordable all-purpose ready-made pickups, at just $32 for their basic model. They sound every bit as good piezo pickups costing quite a lot more. Experimental instrument makers we’ve known have praised these pickups for their affordability, versatility and sound quality for years.
The second type we carry are piezo films. We buy them straight from Measurement Specialties Incorporated, the manufacturer of the film itself. Buying the film straight from MSI, rather than from one of the several companies who use piezo film to produce their own lines of pickups, allows us to pass the best prices on to our customers. We have available one size of ready-to-use piezo film pickup, and plus several more sizes of piezo film ready to be wired up as pickups.
The third type is piezo cable. This is flexible piezo material incorporated into an insulated cable, built very much like the shielded used in many audio applications. coaxial wire. The piezo cable is commonly used to make under-the-saddle pickups in string instruments. In that application, it fits in the slot in the bridge. The cable fits most the bridge slots on most guitars. In some cases it may be necessary either to widen the bridge slot or strip the outer layer or insulation from the cable to reduce its diameter.
More on the piezo film: The ready-to-use pickup is very nicely made, and is fully shielded. (Shielding serves to keep unwanted noise pickup in the pickup wiring to a minimum.) MSI sells this model with a foot of lead wire, but no jack or plug on the end. We can sell it to you like that, or, for a few dollars more, we’ll solder a quarter-inch shielded jack on the end of the lead wire, making it ready for plug and play with a standard guitar cable. (Terminology clarification: I’m using the word “jack” as the female counterpart to “plug.”) If you choose to buy it without the jack, you’ll have a couple of choices as to how you use it, but some soldering and know-how will be required. You can put a jack at the end of the cable yourself. Or you can extend the cable and add a plug at the end, so you can go straight into an amplifier input or signal processor or whatever, without needing a separate cable. Or you can wire it to a volume control on the instrument, or whatever other wiring configuration you want.
The other sizes of piezo films we carry either are not pre-wired or are wired but with unshielded wire and no jack. These have the advantage of being lower in cost, and available in a variety of sizes up to 6″ long, but to put them in operation, you’ll need to do a bit of soldering.
The piezo film and cable we sell come with a how-to information sheet on wiring and shielding, as well as other facets of the pickups and their use.
Piezo-type contact pickups produce an ultra-high-impedance signal that doesn’t travel well over long cable distances. With increasing cable lengths, there tend to be losses in both signal strength and fidelity. In addition, amplifier inputs generally are not optimized for such extra-high-impedance signals. For this reason, the use of a pre-amplifier, located as near as possible to the pickup itself, is often recommended. The pre-amp increases the signal strength and also converts the signal to low impedance, making it less subject to loss over long distances and more suitable for typical amplifier inputs. The pre-amp is not essential, however: the K&K pickups we carry, as well as the piezo films, can be and often are used successfully without a pre-amp. Here are some notes and suggestions concerning the “pre-amp or no?” question.
No Pre-amp: This is the way to go if you want an inexpensive, hassle-free, easy-to-install system. You’ll do fine without the pre-amp if you keep the cable lengths (the distance from the pick-up to your amplifier input) to a minimum – four or six feet should be OK, maybe even 10; much more might begin to be a problem. It also helps if you’ve got a strong signal to begin with — different instruments and different mounting configurations produce different signal strengths. In many cases, you’ll need to to make sure you’re going into a “mic-level” input on your amplifier – if you go into a “line-level” input, the signal may be too weak to provide much volume. While most amplifier inputs are not optimized for the ultra-high impedance of a piezo pickup, typical instrument inputs will still produce acceptable results. (These inputs are usually made to take a quarter-inch plug and may be labeled something like “instrument in.”) Some of the new breed of acoustic guitar amplifiers (as distinct from traditional electric guitar amplifiers) include one input which is optimized for piezo pickups.
Yes Pre-amp: This is the way to go if you are very concerned about avoiding any loss of sound quality and signal strength, particularly when you need to use longer cable lengths. It costs more (you have to buy the pre-amp). The installation may be very simple, or may be quite a bit more involved, depending on the configuration you use (more on this in the discussion of pre-amps below). But tiny pre-amps are available, and these can make for a very elegant set-up with the pre-amp either on the instrument itself, or clipped to the player’s belt, or in some other convenient arrangement. The pre-amp will require a power source. Typically they use a 9-volt battery, and as power consumption is minimal, battery life is generally quite long. Some have the capability to operate off of phantom power, which is a system by which a tiny amount of power can be taken from the main power amplifier through the instrument cable. Here at Experimental Musical Instruments we carry two excellent, very small pre-amps, the K&K Pure Preamp and the Fishman Powerjack. Both are well suited to the kinds of needs Experimental Musical Instruments people are likely to have, but they have very different features — you can read about them in our catalog pages.
Where to get preamps: From us! Click one of the links above.
What kind of power amplifier to use?
Following the pre-amp in the signal chain, the power amp is the main amplifier that drives the speakers. I’m not remotely up-to-date on all the different brands of amplifiers, so I can’t make recommendations, but a couple of rudimentary general observations might be helpful. First: Since everybody’s little brother once tried to learn to play the electric guitar, the world is full of guitar amps. You can plug an instrument other than electric guitars into a guitar amp, and it’ll work — people do this all the time — but guitar amps generally do not provide a flat frequency response over the full audio range. For instruments other than electric guitars, including acoustic guitars, you probably want the full range. For an amp that is designed to reproduce the full spectrum, you can use a PA (public address) type amp, a keyboard amp, a “powered speaker”, or even a good living room stereo amplifier if it’s powerful enough and has the right sorts of inputs. Particularly useful for this sort of application might be one of the new wave of amplifiers designed specifically for acoustic guitars, since many of them provide extra features that are helpful in getting the best out of pickups. You’ll probably need something with a quarter-inch, high-impedance input available, which shouldn’t be a problem since that sort of input is standard for musical instrument amplifiers. You can also run the signal through a mixer, if the mixer provides such inputs. For running through a mixer which does not provide such inputs, you can send the signal from the pickup to a device called a direct box or a DI, which converts the signal to a form suitable for the mixer’s microphone inputs.
A few more words on inputs
Many amplifiers have more than one input for you to choose among when you plug in. Manufacturers use a variety of labels to identify the inputs on their amplifiers. The main distinction to be made is between mic level and line level inputs.
Mic level inputs are made to take a very low level signal; they route the signal through a built-in preamplifier before sending it to the main power amplifier. If you’re not already using a preamp with your pickup, you may need to use a mic-level input. Not all amplifiers have mic level inputs.
Line level inputs are made to take a stronger signal. If you’re already using a preamp with your pickup, it may be suitable to go into a line-level input on the main amplifier. Also, some pickups produce a signal strong enough for a line level input even without a preamp.
Some pickups produce a signal level somewhere in the middle between mic level and line level. To accommodate such situations, many inputs have switches or knobs that allow you to select a suitable middle ground.
If you put too strong a signal into a mic-level input, the resulting sound will be distorted. If you put too weak a signal into a line-level input, you won’t get enough volume, or you’ll get a lot of background noise as a result of having to boost the amplifier’s gain too much. Signal strengths vary over a wide continuum and the distinction between the two levels is not absolute, so you may need to experiment to see what works best for your application.
Another distinction is between inputs designed to take a high-impedance signal and those designed for low impedance. Piezo pickups and magnetic pickups both produce a high-impedance signal. In most cases (though not all) you can keep things straight by observing the kinds of plugs the inputs are designed to take. High-impedance inputs are usually made to take the quarter-inch phone plugs that are typical for musical instrument cables. High-quality microphones, on the other hand, are usually low impedance. Low-impedance intputs usually have the three-hole XLR connectors typical of mic cables.