How Do Acoustic Electric Guitars Amplify The Sound?

the JBP acoustic

The question has been posed;

How do acoustic electric guitars amplify the sound?

I’m not an expert on this by any means, but an electric acoustic amplifies the sound in a number of ways:

1. The same way, initially, as any other acoustic guitar.

The strings, tuned tightly down the length of the neck from the nut to the bridge, vibrate. The vibrations travel thru the bridge and throughout the frame and trusses of the wooden structure. The flat (usually some kind of spruce) top vibrates much like a stereophonic speaker cone, and the actual sound of the plucked or strummed strings travel thru the sound hole and into the open chamber of the guitar. ALL of this vibrational sound resonates back out the sound hole, much like lava out the top of a volcano.

In essence, the body of the guitar, and the flat top in particular, act as an acoustic amplifying chamber.
Some specialty guitars called resonator, or ‘Dobro’ guitars, use a metal speaker pan (of sorts) built into the frontal face of the guitar to amplify the guitar string sounds mechanically.

2. A small, battery-powered pre-amplifier is mounted in the guitar, with controls for the player to make adjustments to the bass, middle, and treble, as well as the overall amplified volume. This pre-amp is wired to a pickup mounted somewhere in the guitar. When a guitar cable connects the guitar to an amplifier or PA system, that electrically-conveyed signal is sent out to the speakers, and then of course, the audience.

This is not to be confused with an aftermarket ‘drop-in sound hole’ pickup, such as a Lace electromagnetic model.
Those pickups don’t rely upon an onboard pre-amp, and they just mount into the sound hole, and their own dedicated cables goes out to the amplifier or PA.

3. The most common type of pickup used in acoustic-electrics is a bridge-mounted ‘piezoelectric’ pickup.
Acoustic guitars and basses, upright basses, fiddles, and cellos typically use a piezoelectric pickup, especially when a microphone isn’t appropriate for a given stage set-up.
A piezoelectric pickup uses pressure to create a current. The current is in close relation with the frequency of the source, in our case, the frequency of the strings vibrating as they create pressure on the pickup mounted in the bridge.

The generated voltage of the piezo-electric system in a guitar is very small. So small that you need a preamp to boost the signal.
The problem is that the piezoelectric pickup is also very percussion-sensitive, so it tends to bark rather loudly when you strum or pick with any force at all. This means that the preamp must afford some compression.

Electromagnetic pickups (like in the sound-hole models or in solid-body electric guitars) sound warmer, more natural, and organic than piezo pickups. This accounts for the typically crisp, trebly sound of those instruments that sport the piezos.

Image of a JBP Acoustic Electric Guitar posted by Sparky2

So... what do you think? Please leave me a comment.

8 Comments:

  • Vale: Fascinating :) I always wondered how it worked, thanks for taking the time to explain it!
  • kcbuck: Cool Bananas Mr. Sparky... Well done and very informative to boot.
  • kcbuck: All of my acoustic guitars are straight acoustics. I guess I’m a traditionalist at heart and only by regular, none of that fancy dancy crapolla junk like those tripe stuffed Oreo’s or the thins. However, the double stuff Ore0’s are my new regular so I guess there is a little hope for me... :)
  • Sparky2: Sadly, I am not allowed to eat Oreos, nor any other sort of cookie, cake, donuts, or sweet treats.
    I love the look and the smell of them though.
    But I have to watch other people eat them.
    On that note, somebody brought in a bunch of candy canes to the office yesterday. One box of them was interesting; they were black and white striped, and (so the box claimed) tasted just like Oreo cookies.
    I’ll be interested to see what the girls had to say about that after they tasted one.
  • kcbuck: Well come on over and you can watch me eat them and I’ll provide the Shiner too... Merry Christmas Bud.
  • Vale: Oreo candy canes? Did you find out how they tasted?
  • kcbuck: Sparky can’t eat them and I only eat regular O-R-E-Os or other snack stuff. None of that weird $hit like Peppermint O-R-E-Os or Vinegar Potato Chips, only regular or Original.
  • Vale: :)

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