HomeNotes on Amplified Fiddles

Part 2: Pickups

As discussed in Part 1, if the stage volume is quiet enough, a microphone and PA system is the most natural-sounding way to amplify your fiddle. However, in louder bands, you will need a direct pickup. This is usually the case if drums and electric guitars are involved, as in a country band. A direct pickup is a transducer that senses an instrument’s vibrations without involving the medium of sound transmission, air. (I’ll shorten “direct pickup” to just “pickup” from here on.) As in Part 1, my remarks are mostly theoretical, and where I name particular brands, these are not endorsements.

Several types of pickups are available for fiddles, as a web search will reveal. (When looking around, be sure to read Stacy Phillips’ article at http://www.allthingsstrings.com/layout/set/print/Articles/Market-Report/Picking-a-Violin-Pickup. It’s a few years old but still relevant because fiddle pickup technology advances rather slowly). There are temporary “contact” types stuck to the body or held in place with a wrap-around strap. A more permanent type is embedded in the soundpost. At least one senses the motion of steel or steel-wound strings in a magnetic field, electric guitar-style. However, most are associated with the bridge--either spring-loaded and inserted into a cut-out, secured by set screws, or embedded in a new bridge.

Thus, some fiddle pickups are more permanent than others. The body contact and bridge-insertion types are temporary, and they require trial-and error to find the best spot for good tone. Think twice before using any sticky pads or putty, especially if you have a fine violin. A bridge or soundpost with embedded pickup is best fitted by a luthier, essentially permanently, since un-installation is also an expert’s job. The magnetic pickup I’ve tried (by Bowtronics) is quite permanent, as it is glued to the end of the fingerboard.

Getting the pickup’s signal to a preamp still requires a cable in most cases, but wireless solutions are gaining popularity. The generally accepted method for mounting an output jack is a Carpenter jack, named for its inventor. This assembly (preferably including a standard 1/4-inch female jack) grips the side of the violin's body the same way a chin rest does, for minimum effect on acoustic tone. Carefully route the wire between pickup and output jack to avoid contact with the body. Such contact can mute the acoustic tone or add a rattle.

The following photo of my heavy-duty (and just plain heavy) student-grade fiddle shows examples of two different pickups, a Carpenter jack, and (incidentally) a build-up of rosin most fiddlers would never tolerate. Don’t let this monstrosity scare you. As an adventurous audio engineer, I like to try different things. Two different pickups and a Carpenter jack fitted with a pickup selector switch are absolutely unnecessary for most players. As noted below, I prefer the bridge pickup; I don’t want you to glue a magnetic pickup to your finger-board unless you are certain that’s the sound you want. Some players do use two transducers simultaneously, but these are usually a bridge pickup and a small fiddle-mounted microphone. Such rigs have a stereo (two-channel) jack and cable coupled to a special “blender” preamp (see Part 3). But most electrified acoustic fiddles have only one pickup (usually an in-bridge type) and a monaural (one-channel) output jack.

Photo of Clark's fiddle with two pickups labeled.

This may not apply to the temporary types, but it’s reasonable to expect that a pickup doesn’t alter the acoustic sound of the fiddle. Keeping the instrument sounding good when “unplugged” makes it most versatile. Bridges with a built-in pickup can meet this expectation, are most popular, and are the type I prefer. I tried a pickup that clamps to the bridge with set screws, but it muted the acoustic tone. Bridges with a designed-in pickup are better. And be warned that a magnetic pickup, even though it does not add mass to the bridge or body, theoretically alters the tone by slightly attracting the steel strings in its vicinity. This is called magnetic damping.

The best acoustic instrument pickups use the piezoelectric effect, in which certain crystalline materials generate electricity in proportion to changes in mechanical stress. These are called “piezo pickups” for short. Electrically, they have a high output impedance, much higher than a magnetic pickup has. In fact they are the highest-impedance transducers in the audio world. For best results, a piezo pickup should feed a preamp or direct interface (DI Box) whose input impedance is extremely high--a million ohms (1 megohm) or more. The inputs of many guitar amps and all passive (transformer-type) DIs are not optimal. A good quality cable that’s no longer than necessary is recommended.

An ideal pickup would capture a fiddle’s exact acoustical sound. Unfortunately, this is impossible. As I said in Part 1, all of a fiddle’s many parts conspire to form its voice, and this is only realized some distance away from its body. Vibrations in no single part of a fiddle--string, bridge, sound post, any point on the front or back plate, the air near an f-hole--can exactly represent this whole. A hologram, in which dissected bits contain all the information of the whole, is a poor analogy for a fiddle.

However, experience has shown that a piezo pickup embedded in the bridge is a good compromise. The bridge is where energy from individual strings is mixed and efficiently couples to the body (more about this in Part 4). With its complex set of resonant modes, the body processes these vibrations and couples them to air. This signal path is reversible; if you are not touching any strings and someone plays an A, your own A string comes to life. This means that information (vibration) in the bridge is more an equilibrium than a one-way flow. So perhaps it’s an urban myth that a good bridge pickup in a cheap fiddle sounds as good as it does in a fine violin--quality of the body affects the motion of the bridge. But, between cheap and good fiddles, the difference in acoustic voices will be greater than that of their electric voices.

To visualize differences between my fiddle’s two pickups and its acoustic sound, I bowed the open A and analyzed the frequencies within recorded signals (using Digidesign’s Sound Designer II software). The frequency composition (or spectrum) of each sound is shown in the picture below. The microphone (AKG C-1000S) signal represents the acoustic sound; at 12 inches, it’s distant enough to “hear” the whole instrument but close enough to minimize the effect of room reflections. The piezo pickup is an embedded-in-bridge type from Barcus-Berry and the magnetic pickup is from Bowtronics (see photo of fiddle, above). The pickups were hooked to my custom preamp (see this link), which has one-megohm input impedance and was set for flat equalization (EQ).

Spectra of violin playing open A string, as recorded with three different transducers.

The harmonic composition of the two pickups’ signals differ from each other and from the acoustic signal. All contain the fundamental tone we hear as an A (440 Hertz). But the 2nd, 4th and 5th harmonics are relatively over-loud with the magnetic pickup, while emphasis of the 2nd and 3rd harmonics is flipped for the piezo pickup versus the acoustic sound. This exact pattern of differences won’t hold for other pitches, but the point is there are differences. They are audible and can be addressed with limited success using EQ.

Of my fiddle’s two pickups, the in-bridge piezo is my favorite. In Part 3, I’ll talk about how I like to amp it up, along with the amp and preamp options available to you--the fiddle player who wants to be loud.

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