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The stringing of an acoustic electric guitar with an undersaddle piezo pickup suggests a different technique other then following the procedure from the former article: Stringing an Acoustic Guitar.
Recently, we had discussion with the head luthier/technician at the Taylor Guitar Factory about uneven or unbalanced sound happening on acoustic guitars with a piezo system. Below is good information to understanding a piezo system.
Piezo ceramics, or crystals, are materials that generate an electrical charge when subjected to stress. Piezo pickups are placed under the string saddle to convert string and top movement into an electrical signal that can be amplified.
Proper balance of a piezo requires a precise fit of the string saddle, the saddle slot, the piezo, and the strings. If any one of these elements are out of balance it throws off the balance thus poor or faded string sound(s).
The most important of these elements is the saddle. There must be even pressure from each string to the piezo element/pickup. Moreover, the saddle must be flat, square and true in the saddle slot. A jammed or overtight saddle in the slot will impair the piezo sound or cause a hum. If one cannot gently lift a saddle from the slot then the saddle is binding.
A string saddle should be clean of debris and able to be re-inserted in the slot without binding or being forced in the slot. Also, the saddle ends should be rounded smooth as opposed to square. Finally, the saddle bottom should be squared.
A saddle slot (bridge slot) must also be flat. If uneveness is present then sound will be unbalanced and requires that the slot be leveled with a leveling tool.
A piezo must be correctly aligned with the guitar strings. If a piezo is offset strings are not making contact with the individual sensors in the piezo pickup.
When restringing its best to tighten the middle strings first so pressure is applied to the saddle center. Then add and tighten the 2nd and 5th strings. Last, install and tighten the 1st and 6th strings. Finally, tune to pitch and apply string tension evenly. That is, tune to pitch on all strings evenly rather then one string then another.
Also important is the height of the saddle that effects the response and balance of the piezo. A string saddle must be tall enough for a correct string angle over the saddle and angles downward to the bridge/string pins.
If a saddle is too low (when trying to lower action) insufficient string down pressure is the result thus poor sound happens. Further a low saddle becomes more flexible and does not transmit string vibration efficiently as a full height saddle.
If a saddle is too tall the saddle will lean forward offsetting string pressure on the piezo. A leaning saddle will bind at the front and back of the saddle slot.
Finally, if everything is perfect and there is still weak or an unbalanced sound then apply a piece of cellophane (scotch) tape to the bottom of the saddle in the area that sounds weak. Make sure to not bind the saddle then restring as described above.
If all fails then an electrical or piezo problem is at issue. Have a qualified-trained technician review the guitar and its electronics.
Addendum: Copper wire under saddle piezo systems:
Our shop comes across copper wire piezo systems that are usually found on import guitars.
These wire under saddle systems are poor, tend to flatten, and develop weak sound, or hum, over time.
In our opinion only two remedies resolves wire piezo problems. One, replace the wire with a crsytal
ceramic piezo. Two, shim the copper wire to improve weakened sound.