Amplification of the acoustic guitar
The acoustic guitar (in all of its various forms, from classical with nylon strings to folk with bronzed strings to the flamenco guitar) has its own natural volume that is determined by its resonance chamber, a volume that is far superior to that of a non-amplified electric guitar. There are many situations in which it is necessary to amplify the acoustic guitar. For instance, playing an acoustic guitar in a group whose instruments are amplified by the P.A., makes the amplification of that guitar mandatory if its natural volume isn't insufficient.
Also a concert of one, two or three guitars could need amplification, possibly due to environmental demands of where the concert is being held.
It is a more complicated procedure to amplify an acoustic guitar than an electric guitar, because of the fundamental fact that you have to recreate the acoustic sound of the guitar. After having read the previous section, you can imagine that today these problems have less importance, because today you can even simulate an acoustic guitar with an electronic circuit connected to an electric guitar. But can you completely give up the physical contact with an acoustic guitar? Certainly not. We will now look at the various procedures to amplify the acoustic guitar.
Using modern P.A. amplification systems you can reproduce the sound of an acoustic guitar with absolute fidelity.
The best system today remains the microphone, even if there are limitations when playing live. The problems that may arise are these:
The fact remains, as I said before, that a good microphone surely gives better results than any other system and for this reason it is the most common system for someone who wants to obtain maximum sound quality.
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At times it can be interesting to place two microphones in different positions (one in front of the hole and the other on an angle of the resonance chamber, for instance), calculating that the inclination, especially of the microphone set in front of the hole, will give more bass if placed above the sixth string and more treble if placed below the first string. A central position would obviously be more neutral. The correct position comes from the type of guitar that you are using,
because every guitar has a preference for one particular range of frequencies in the sound spectrum and for this reason it could be useful to try various angles to find the best sound from that instrument. One last recommendation: the distance of the
microphone is very important because it could influence the feedback from other instruments.
It is possible to install a magnetic pick-up on the acoustic guitar similar to those used for electric guitars. This pick up responds to the vibration of the string, but is minimally influenced by the resonance chamber and therefore is used very little, and the resultant sound would be half way between the natural sound of the instrument and the electric sound of the pick up. With this system a lot of the sound qualities of the acoustic guitar would be lost. It is only recommended in the case where you want to spend only a little without working on the body of the instrument.
Currently, the best system to amplify an acoustic guitar without the aid of the microphone is the piezoelectric transducer. There are various models and application possibilities for this type of pick-up. The most classical consists of a small block of crystalline or ceramic material encapsulated in metal or plastic, with two outputs soldered to the surface. This device is attached to the instrument and works on the principle of the piezoelectric effect. It is stimulated by the vibrations that are propagated through the wood of the guitar from the strings. These stimulations allow the escape of electrons on the side adjacent to the transducer, making all the charges negative on that side, when the vibrating table moves toward the outside.
When this moves toward the inside, the electrons migrate toward the opposite side reversing the polarity. These variations will be transmitted in the form of alternating current through the two output cables. In some cases the signal can be so weak that you need to use a preamplifer to strengthen the signal. Many acoustic guitarists prefer to amplify their instrument through the use of both piezoelectric transducers and microphones, mixing the various sounds through the mixer and getting probably the best overall sounds. In any case a problem to always keep under control is feedback. This effect, nice for many electric guitarists, is a nightmare for acoustic guitarists. To avoid this, you first of all need to keep the instrument away from it's own speakers and never in front of them. Next be careful with EQ controls, as the "whistle" tends to develop at certain frequencies (especially the highs), while the typical resonance prefers the low frequencies. Next you must verify the frequency cuts of the reverberations, because they could create some very annoying resonances. You should always test the position of the microphones during the soundcheck, so that there are no surprises at the last minute. On the market there are some models of amplifiers built especially for acoustic guitars. They are adapted to the specific frequencies of the piezoelectric picks ups, either preamplified or not. In many cases these amplifiers are equiped with internal effects (such as chorus and reverb) as well as effect outputs to externally connect a modulation unit, delay or reverb. The quality of the sound varies from one amplifier to the next, but the fussy prefer the microphone or the connection directly to the mixer. For those interested in the amplifiers, there are the various acoustic models by Trace Elliot, even the models with only the preamp (surely among the best), the Marshall Acoustic series and the most recent Compact by Audio Electric Research. Another acoustic preamp is the AD-5 by BOSS, which has a good quality-price relationship.
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