Most people these days want a 'plug and play' instrument whether for on stage work or for home enjoyment through an acoustic combo amp. Pickup technology has moved forward in recent years and thus there are many systems available on the market, each company claiming to produce the most natural sounding device.
For the most faithful reproduction of your instrument's tone, a condenser mic will do the best job. It is still more common than not to see Flamenco guitarists for example using a small diaphragm, directional condenser microphone on stage rather than a pickup to cope with the dynamics achieved with this style of playing. When amplifying at volume especially with monitors, however, problems with feedback are frequent and of course positioning of mics in relation to an often moving instrument is difficult and sometimes unworkable. A pickup system then, needs to offer some of the dynamism and natural reproduction of a mic but with a stability and feedback resistance at higher volumes.
In any system there is a potential three stages.
1. The Transducer (pickup or mic) This is where vibration is turned into electrical energy.
2. Pre-amplification where this signal is boosted and better matched to the next stage of amplification. Also where a first layer of tone control and filtering can occur. These can be on board the instrument or offboard in a floor or belt clip box. Both are battery driven and can sometimes be mains fed and occasionally phantom powered.
3. Amplification Where the signal from the transducer (via a pre-amp if utilised) is boosted to a level enough to drive a loudspeaker unit. Usually this would be in a combo amp (amp and speaker in the same unit) or in the power amps of a P.A system.
Getting the right combination of these elements for the player is essential, each obviously having their own requirements. Listed below are some of the elements we can consider when choosing a system.
Contact pickups These transducers come in a variety of forms and are designed to stick on to the instrument (usually on the soundboard). Good quality models can produce a very natural and dynamic tone if positioned correctly but always need a pre-amp with EQ as a minimum. A notch filter and sometimes a semi parametric EQ is recommended to help reduce feedback problems. A potentially rewarding but not completely trouble free option. Can work well blended with another pick-up. Can be easier to work with on small instruments such as mandolins and ukes.
Undersaddle transducers Nowadays, these are the most common type of pickup found on acoustic guitars and usually offer a relatively trouble free, stable sound. In the past these pickups have sounded "plasticy"or "quacky" but top quality current models have a clearer, more natural tone and greater dynamic potential. There is a small drawback in that by putting a barrier between the saddle and the bridge of the instrument you can compromise very slightly the unplugged acoustic tone.
Magnetic Pickup This style of pickup you would find on a electric guitar but there are models available designed to be used with bronze and phosphor bronze wound strings. They usually clip into the soundhole. Good models are usually humbucking, produce a very stable sound and work well at higher volumes and some have microphone blend options or have a built in microphonic action. This helps to make for a more natural and transparent tone. Another great all round option - the models using a microphonic element are fantstic for more gentle fingerwork as well as strumming.
Internal or external microphone These are usually mounted on a gooseneck and clip onto an internal brace or on the outside of an instrument (the latter being more common on mandolins). Can be very prone to feedback but can work very well in conjunction with a magnetic pickup or undersaddle transducer to add a more natural dynamic to the sound. There are some systems available that incorporate the two.
There are now chips on the market which can digitally reproduce the sound of other instruments. All you need is a standard pickup system and you can choose from a variety of 'miked' sounds sampled from other instruments. This is a relatively new technology and is developing rapidly.
As mentioned above, pre-amps can come in different forms on and off the instrument. They are important because they transform a weak signal from the transducer to one that is more compatible with the input of the final amplification stage in terms of impedance and gain. This tends to warm up the sound in the process. Many pickups these days come with some form of onboard preamp usually as part of the jack socket if no onbooard tone controls are required or as a unit which mounts internally on the side of the instrument with a panel on the outside. These are usually powered by a 9v battery.
Most guitar-sized or smaller stringed instruments require a mid or upper mid cut when being amplified and so it is best to shape your tone on stage to give the sound desk less work to do on your signal. When fitting a system to a good guitar and tone controls are required I often recommend to use an offboard pre-amp to avoid cutting into the side to insert a panel. This means a system can more easily be changed in the future and of course lessens the impact on your lovely instrument! These usually have a 1/4 inch jack input and an XLR and/or 1/4inch jack output. A balanced XLR output means you can use your pre-amp as a D.I. for stage work.
There are many acoustic amps on the market now, some better than others of course. They are built to more faithfully reproduce the clean, clear and dynamic tone of acoustic instruments and usually come with broad tone control and an array of feedback busting devices. A good quality acoustic amp can be a great on stage asset as you can direct input from the amp to the P.A thus eliminating the need for a pre-amp with tone control. The speaker will also act as a monitor. Can be a great on stage asset but tends to compress and colour the tone to a greater degree than a high quality pre amp.
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