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Tuesday, March 25, 2014

Guide to Acoustic Guitar Transducers

Acoustic guitars require transducers to amplify the sound. This article discusses the different options commonly available.

What is an acoustic guitar transducer?
An acoustic guitar transducer converts vibrations into electrical energy. The simplest example of this is an instrument microphone that you can place near the sound hole of the guitar. Miking an acoustic guitar produces a natural sound, but the volume level is affected by the guitarist's movement.
Under the saddle transducer
An under the saddle transducer is placed between the bridge and the saddle. It can increase the saddle height so the bottom needs to be shaved to compensate. A small hole is drilled on the bridge for the wires, and a bigger hole is drilled where the endpin is located for the endpin jack. Under the saddle transducers capture the string vibrations and are less susceptible to feedback, making them ideal for stage use. However, these sometimes have a plastic sound although some manufacturers have developed transducers that minimize this limitation.
Under the bridge transducer
These small transducers are glued inside the guitar, usually where the bridge is located, and detects vibration from the soundboard. These results in a sound similar to a miked guitar, but is prone to feedback. Careful speaker placement can fix this, but may be difficult if you are in a small room. There are also products that let you cover the sound hole to prevent feedback.
Endpin transducer
This type has a mic on the side of a small box that is directly connected to the endpin. The box can be rotated to allow minimum feedback. Endpin transducers capture the sound waves inside the guitar, and produce a sound similar to a miked guitar.
Sound hole pickup
A sound hole pickup is a transducer that is placed under the strings over the sound hole. This works like an electric guitar pickup and is easier to install.
Dual transducers
Dual transducers offer the best of both worlds: an under the saddle pickup that is feedback resistant and one that captures the sound waves for realistic sound. The sound sources are mixed for better overall tone, while giving you the option of adjusting the level of the feedback-prone transducers for live use.
Active preamps
The output of acoustic guitar transducers is low, and onboard active preamps provide an adjustable gain with optional tone control. A preamp located on the upper side of the guitar gives more options like sliders and guitar tuner, but requires a rectangular hole that limits the choice of replacement if you decide to upgrade. Another option is a preamp glued inside the guitar near the sound hole. I personally prefer the latter.
Passive transducers do not have active preamps in the guitar and are generally less expensive. However, they require an external preamp that should be included when preparing the budget.
Direct Input box
Also called DI boxes, these devices match the output impedance of your guitar to the mixer input impedance, resulting in a tighter sound. While it can be argued that the difference in tone may not be noticeable, the output of a DI box has an XLR jack that allows you to connect to any venue that has an available XLR cable for microphones.
There are two types of DI boxes: passive and active. The general rule is to use passive DI boxes for active sources, and active DI boxes for passive sources. If your guitar has a battery, it is an active source.


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