The article that follows will attempt to address the most common issues regarding retrofitting pickups to acoustic guitars. I will not be endorsing or critiquing particular brands.
WHAT TYPES OF PICKUPS ARE THERE ?
There are four types of acoustic guitar pickups :
Combinations of these are also blended into one system by many companies.
- Under The Saddle
WHAT MODIFICATIONS MUST BE DONE TO MY GUITAR ?
UNDER THE SADDLE PICKUP
First,let's define our terms. The "saddle is a piece of bone or plastic which sits in a slot located on the wooden "bridge". The saddle is removable. The bridge is glued to the top of the guitar. On most guitars the strings ride over the
saddle and then pass through the bridge where the strings are held in place by "pins" mad of plastic, wood, or bone. On some bridges("non-pin") the ball ends of the strings seat at the back of the bridge.
"Under the saddle" pickups are thin strips of material which are seated under the saddle, in the slot of the bridge.A wire runs from the pickup element to an output jack, usually located at the strap button area at the endof the guitar.
In some cases the saddle slot must be re-cut to provide a flat surface for the pickup to be seated. Even contact between the pickup, the bottom of the saddle, and the bottom of the slot are essential for proper function of these pickups.
Some pickup systems will include a pre-amp assembly which must be mounted inside the guitar. This is usually done proximate to the soundhole. It can either be adhered with Velcro tape, glued to the inside of the guitar, or screwed on to the neck block. Systems with pre-amps need 9 volt power and in many cases a battery clip must also be located, again, proximate to the soundhole.
A contact pickup is adhered to the top of the guitar with a type of putty. Contact pickups can be adhered to the outside or the inside. For temporary, non invasive, now and again usage, an outside application can be acceptable. But many players either prefer or need a contact pickup and want an uncluttered, "permanent" installation including an endpin jack.
For this installation a hole must be drilled for the jack. Putty holds the pickup in place on the inside of the top of the guitar, usually in the area of the bridge. In the ideal installation, the final location of the pickup is determined by trying a few spots to achieve the best tone vs. feedback resistance, which varies depending on the particular guitar in question. The location of the pickup on a Dreadnaught sized guitar is going to be different than on a cedar topped classical guitar.
Some companies manufacture pickups which are clamped or wedged into the soundhole of the guitar. An endpin jack is an option with these pickups as well. (When I install these I like to install an additional plug and jack inside the guitar so that the pickup can be removed for travel.). A wire can be left dangling out the soundhole if the preference is to minimize affectation of the instrument, but, frankly, if you plan to use this pickup with any frequency, an internal mounted endpin jack is preferable. Some marring of the finish where the pickup is clamped can occur if the installation is not done carefully.
Some microphones are integrated with an end pin jack, and thus require expansion of the strap pin hole. Others clip on to the bracing inside the box of the guitar with the option of running a cord out the soundhole. Still others are adhered to the inside of the guitar with velcro and connect to an internally mounted pre-amp which also has an end pin jack.
From this over view it is clear that the "under the saddle" type of pickup entails the most potential work on, if not modification of, the existing instrument. For most "permanent", less fuss, applications, an installed endpin jack is preferred, regardless of the type of pickup.. So, short of running a wire out the soundhole or having one dangling in front of the instrument, the least amount of modification entails the drilling of a larger hole at the strap pin location. Some guitars, such as those made by Taylor come with a factory sized end pin hole which will accommodate an end pin jack without modification .
HOW WILL EACH TYPE OF PICKUP AFFECT THE NATURAL SOUND OF MY GUITAR ?
Under the saddle pickups are of two types -Piezo crystals - literally, crystals, encased in a sheath of varying materials, and thin strips of sensing material (again wrapped in materials in a range of stiffness).
In Piezo pickups, a manmade crystal sits underneath each string. The pressure of the string creates an electrical energy which, when the string is plucked, is transmitted to the amplifier. Each crystal/sensor is, primarily, triggered by the pressure of a particular string, though it also senses some of the surrounding ambient vibration The spacing of the crystals, therefore, must correspond to the string spacing on the guitar in which they are installed.
In the others, a thin sensor is sandwiched between two other layers of material, the nature of which varies from maker to maker. The contact and pressure between the saddle, the pickup and the saddle slot in the bridge, is just as important as with the piezo crystal sensor, though the particular string spacing is not. In this case, the entire strip "senses" the vibration of the strings and surrounding box, though any given string is only as present as it's particular contact with the sensor (as with the crystal).
Anything you place between the bottom of the saddle and the saddle slot seat has the potential to affect the transmission of the vibrations which travel from the string, through the saddle to the soundboard, and therefore can affect the sound of your guitar .. In some guitars, the addition of a layer between the saddle and the bridge has a distinct affect on the sound. Some guitars, indeed, can benefit from this affectation,(though, often, people don't hear the difference). For example, if a solid wood shim is placed under a saddle, as is sometimes done to raise the string height at the saddle, the tone can be affected depending on the properties of the shim. If the shim is made of the same wood as the bridge, say Ebony, the primary affect will be increased volume because of a slightly higher torquing action on the top by the taller bridge saddle.
But tone can be changed by the material used for the shim as well . If the saddle were replaced and the height achieved by a taller bone saddle, I would expect a brighter tone, since bone, in my experience, is denser than even ebony (the hardest, commonly used bridge material). If a softer wood, mahogany for example, were used, I would expect a mellower tone, due to the softness of the wood (essentially more space between the cells - less dense). On the same principal, a stiffer pickup element (regardless of style) will tend to provide/maintain brighter tone than a softer pickup element. These can be subtle distinctions and may not always be heard, but on some guitars, and by some ears, these effects are very pronounced.
Accepting the above concepts, we can conclude that piezo crystals, being the hardest material used for sound reproduction, have the potential to produce the brightest , clearest tone, and, to the degree that the sheathing is flexible and the sensing element is softer, a softer tone will be produced.(Remember, though, when amplified, the pre amp, if there is one, further colors the tone from this point on.)
The bottom line on under the saddle pickups is that they have the distinct possibility of affecting the "natural" acoustic sound of your guitar.
Contact pickups sense the vibrations of the top of the guitar. The pickup attached to the top of the guitar with strong tape or putty. They are lightweight and generally will not interfere with the natural sound of the guitar.
Soundhole Pickups, which seat across the soundhole, both tighten the top in this area and block the soundhole. Anything that is affixed to the body of the guitar adds weight, and in some areas, such as the back and to a lesser degree the sides, can affect the tone and volume of the instrument. While some parts of a guitar are more directly affecting the sound (top and back), the whole box vibrates when you pluck the strings. Therefore, preamps, battery clips installed to the back sides and even the neck block, soundhole pickups and contact pickups adhered to the top, can indeed have an affect on the tone and volume of the instrument. The degree to which this is noticeable will, of course, be variable, but cannot be denied.
Microphones are usually clipped to a brace or mounted with tape or velcro inside the guitar. They are usually very lightweight, and tend to have little affect on the natural sound of the guitar.
The bottom line is this - the less stuff you put in and on your guitar, the less the "natural" sound of your guitar will be affected.
Also, let's admit that no pickup is going to reproduce the sound of a guitar as we hear it acoustically through our ears. No matter the pickup or microphone, an electronically reproduced tone is just that - an electronically reproduced sound generated by acoustic vibrations. It's not wood, and steel or nylon, or gut, vibrating the air,
it's an electronically generated signal generating a vibration in a speaker cone, which vibrates the air.
WHICH TYPE OF PICKUP PROVIDES THE MOST RESISTANCE TO FEEDBACK ?
Soundhole pickups are certainly the most feedback resistant. They are electrically charged magnets, similar to those used in electric guitars. While they do pick up some vibration from the instrument, most of the sound is triggered by the vibrating strings. This provides a great resistance to feedback caused by ambient vibrations, a problem that the open box of an acoustic guitar is quite susceptible to.
The drawback of the magnetic pickup, though, is that, for many people, the sound is not "natural" enough.
Under the saddle pickups provide a relatively high degree of feedback resistance because the pickup is seated under the saddle and surrounded by the wood of the bridge. This resistance to feedback will vary from instrument to instrument because of a couple of factors - The overall resonance of the box
The depth of the saddle slot in the bridge. A deeper slot puts the pickup closer to
the more vibratory top, and therefore provides less resistance to feedback.
The amount of high volume ambient noise hitting the box and entering
through the soundhole. This an be mitigated to a great degree by a soundhole
The tonal contour of the ambient sound hitting the box and entering the
The volume setting for the signal coming from the pickup. The higher the
setting, the more likely to feedback.
Contact pickups provide little resistance to feedback, because they are seated directly on the soundboard and are greatly affected by any ambient sound which hits the soundboard.
Microphones, for obvious reasons, are the most prone to feedback.
The best way to prevent feedback, regardless of the pickup, is to keep the volume at the pickup as low as possible and let the amp, boost the signal.
WHICH TYPE OF PICKUP GIVES THE MOST NATURAL SOUND ?
First, it should be said that a reasonably "transparent" reproduction of the sound of many guitars yields a result that may not be wholly satisfying. A good pickup with minimal pre-amp tone contouring is going to give you the sound of your guitar, warts and all. If your guitar sounds thin, this will be the case when reproduced, if it is tubby, same correlation. Often when people are displeased with the resulting sound from their guitar it is the guitar and not the pickup that is to blame. But a nice sounding guitar, with a properly placed, quality pickup can sound wonderful. It is also true that a poorly installed pickup will also contribute to bad sound.
Some guitars which have a fabulous amplified sound don't sound as good acoustically. The circuitry in the in the pre -amping provides a pleasing tonal contour which isn't found in the instrument. The strings just trigger the signal, so a pickup system with a lot of pre- amp contouring can be a good choice for a guitar with less than ideal natural tone. And conversely, a relatively transparent system is often the best choice for a guitar with a pleasing natural sound.
A good argument can be made that for a quality acoustic guitar a well placed contact pickup combined with a microphone can provide the most "natural" sound. But the sensitivity of this combination to feedback can make it unacceptable for high volume settings.
DO I NEED A PRE-AMP ?
First we should clarify that there are two kinds of pre amps - integral and external - and some external pre-amps are mounted on the outside of the guitar, others are independent units which are plugged into on the way to the amplifier.
Some pickups come with a pre-amping circuit wired to the endpin jack. You won't see it, and you cannot adjust it, but it is there. The signal from your guitar travels through it and there is some contouring of the tone, as well as a boost in the power of the signal. This style is non-adjustable.
In others, the pre-amp is mounted inside the guitar, in the area of the soundhole. In some systems you have some ability to adjust the tone of the signal, and/or the volume, but there is not a broad tonal palette which is adjustable.
Some companies offer three and four band pre- amps which can be mounted on the side of the instrument, or plugged into as separate units. For some players, this ability to control the sound and the convenience of having it right at hand is preferred. But there are good reasons for not wanting this type of system as well.
The longer your signal chain, the more circuits you place between your strings and the amp, the further you are getting from the "natural" sound of the box.
There is no doubt that a pre-amp gives you more control over the sound of your guitar,
and in some onstage situations the ability to contour tone for feedback prevention is essential. While some players are looking for that elusive "natural" sound but louder, others want to play an acoustic in an amplified, band context; so they can compete with other loud instruments but be playing an acoustic.
The bottom line is that Pre-amps give you more control over the tone of your amplified sound, but the least amount of circuitry between the guitar and the amp is likely to provide a more "natural" sound.
DOES MY AMPLIFIER AFFECT THE SOUND ?
Absolutely. no matter what type of system you have, the amplifier also figures into the "sound" of a guitar which is being enhanced by a pickup or microphone. When reproducing acoustic guitar the most transparent (natural) sound is had by a system which gives the least "color" to the signal. Solid state, as opposed to vacuum tube, amplifiers have the potential to provide the most transparent sound, and, to most ears, can produce the most "natural" sound.
It should also be noted that digital technology has advanced such that tonal contouring is a very precise art and, indeed, wholly electronic signals ,even to the most discerning ear, can reproduce a "natural" sound. So there is indeed an argument for forgetting the high end acoustic box and just investing all your cash into a fine digital processor.
Fundamentally, the amplification system is a significant factor in the signal chain, and must be given a high priority if the goal is the "best" sound. But being the first step in the signal chain, the pickup is the most fundamental . The best thing to do is try as many different types of amps with your guitar before settling on one. And these days, there are many amps designed just for reproducing acoustic instruments
In the forgoing article I have tried to provide an over view of the most common concerns related to retro-fitting an acoustic guitar with a pickup. In one sense, it's hard to go wrong these days because there are many high quality pickups on the market, but it is also hard to pick the right one for your needs. Ask these questions as you enter into the fray -Why are you amplifying your guitar and what situations will you be playing in ? How much modification will you accept ? Have you thought out the entire signal chain that you will play through ? Hopefully, this information I have presented will be an aid in deciding which type of pickup is going to best suit your guitar, and your needs.
Steve Carmody has been repairing guitars full-time since 1990. Questions? GuitarRepairShop@aol.com