Riaan-Combrink
Sorry guys, just wanted to add to above post.
The same edition carries the following article by the well-repected Adrian Legg. Seems aposite to this discussion:
Teaser:
Amplifying acoustic guitars for live performance is an inherently compromised process, in which one attempts to reconcile the need for volume with inevitable loss of the true character of the original sound. Has the amplified acoustic in fact become a different instrument?
Adrian Legg
Once you take your acoustic anywhere near a sound system, be it a PA or amps, it ceases to be an acoustic and becomes part of a complex chain of technical and positional variables between your fingers and your audience's ears. What you are trying to achieve is as decent a facsimile of your acoustic as may be allowed by your pickups, the volume at which you need to operate, the quality of the sound system, and the room in which it is all going to happen. You are definitely not going to get 'your original acoustic sound, simply louder,' although there may be traces of it at some levels. There is no single solution, only a range of compromises.
VOLUME SCALE
I've found it easier to consider all these variables and compromises on a scale, at one end of which is the tone you would like to have and at the other end of which is the volume you might be required by the gig circumstances to achieve. My scale is reduced to very basic categories. Within each one there are very many subsets of characteristics and tweaks that could move an individual instrument, pickup, situation or combination of all three in either direction — some of these will occur to the reader instantly.
At the bottom of my scale is a stand microphone, which is as close as you'll get to acoustic using a sound system. In fact, in small rooms you won't get the mic much louder than the natural sound of the guitar before it feeds back anyway. Remember that speech is as loud as a strummed guitar and singing is louder. A mouth is focused, very directional, and can be placed right up against a microphone. For live, you need a directional microphone (hypercardioid or cardioid), but the closer you get to it the more you will get proximity effect — a disproportionate and ultimately crippling increase in bass response. A capsule with inherent or switchable bass roll-off is therefore essential.
At the other end of my scale is the solid-body electric, an instrument designed for delivering a specific and relatively narrow range of tone at a very high volume level where most acoustic aspects have vanished. The pickups are narrowly focused, designed and built to be as physically insensitive as possible, and are within a few millimetres of the strings.
Between the two extremes are points at which a fluid set of compromises will work, where it becomes necessary to trade lovely qualities of tone for dubiously secure volume in order to be heard! For example, a piezo soundboard transducer, given a nifty bit of parametric tweaking (of which more later) can sound almost acoustic, but will feed back at a low sound level. It will be adequate for strumming and supporting vocals in a small folk club and might be enough for solo fingerpicking in the same venue, but in a large bar it wouldn't be enough for anything but hard strumming behind vocals. For a bar — if you wanted to fingerpick — you'd have to go to a soundhole magnetic, but that's not going to sound close to 'acoustic', except in the sense that people might have become conditioned to accepting it.
Caveats arise immediately. Firstly, nobody listens to an acoustic guitar with their ear pressed against its body, which is very roughly equivalent to the audio quality of the signal the piezo soundboard transducer is producing. Secondly, a magnetic pickup will retain some of the tonal absorptive/reflective qualities of the guitar, as reflected by the string vibration in the magnetic field, and it is certainly going to still be sensitive to the fundamental frequencies of the soundboard and the air box cavity. So, at its upper limit, the 98Hz G is still likely to be the first note to take off unpredictably into roaring feedback. Thirdly, your natural acoustic guitar's sound comes off the guitar in various ways: from the soundhole, from the top, from the sides and from the neck. The sound is full of complex phase and directional information that makes it rich and diffused. And whatever small part of that you succeed in collecting in a pickup will be sent amplified to a speaker, which will send it out, all at once, in a restricted band and in one direction.
Also, when you pluck a guitar string there is a tiny delay before the body timber reacts and starts vibrating. A piezo pickup, soundboard or undersaddle reacts immediately and can produce a very unpleasant attack transient through the sound system. A magnetic responds less rapidly, but notes get louder as you play higher up the fingerboard. Each is a compromise.
TWO PICKUPS ARE BETTER THAN ONE?
Acoustic amplification scale — the bottom is as close to acoustic as you can get using a sound system, and the top is where most acoustic aspects have vanished.It is perfectly possible, and quite common practice, to use two or more of the different kinds of pickup available in combination. For example, one might use a soundhole magnetic to produce the bulk of the low mids and bass (as far as may be possible, given the local feedback threshold), and a piezo soundboard transducer to overlay more woody mids and highs, rolling off the low mids and bass on this to get away from the piezo's extra sensitivity there to feedback. In this instance, it is important to bear in mind that susceptibility to feedback is now not just related to the magnetic, but is governed by the proportion of sound coming from the piezo, and this is a lower threshold than the magnetic on its own. One must remember that the problem is not so much in the pickup's insensitivity, but in the acoustic guitar's inability to generate loud and focused sound.
There are combination units sold nowadays, and a popular one for taps/drum sounds combines a soundhole magnetic and an internal microphone. The mic picks up the taps/drum sounds very well and can be set at a very low level, because the percussive noises are relatively loud by their nature. This combination may be less successfully used for a fingerpicking style without percussion, because the volume range at which the mic contributes anything useful to the tone here is very narrow and has a very low feedback threshold.
That's as much as we get for free, I'm afraid ...
