Why is an Acoustic Guitar so much LOUDER than an Electric Guitar?

[The Observer]

MSC,

Pay the price because energy is built up?

     My point is that the acoustic chamber of an acoustic guitar amplifies sound.
     It does this by, as you say, by building up energy in a certain local (the acoustic chamber).

It is "amplification" - but it is not *net* energy amplification.

      First... you can't have it both ways.

      Second ...sound waves 1000 times larger come from the Chamber (than from the string) & also sound out longer.
                       and you think there is no amplification of Sound?

                                             I have one question for you.
                         "How tall would you be if you were 1000 times taller?"

Sincerely,
                 The Observer

P.S. It makes me a little nuts when it appears
               I'm only person who thinks the acoustic chamber of an acoustic guitar amplifies sound...
                                 so forgive me if I sound a bit defensive. ;o)


             

[utilitarian]

MSC,

Pay the price because energy is built up?

     My point is that the acoustic chamber of an acoustic guitar amplifies sound.
     It does this by, as you say, by building up energy in a certain local (the acoustic chamber).
     
      First... you can't have it both ways.

      Second ...sound waves 1000 times larger come from the Chamber (than from the string) & also sound out longer.
                       and you think there is no amplification of Sound?

                                             I have one question for you.
                         "How tall would you be if you were 1000 times taller?"

Sincerely,
                 The Observer

P.S. It makes me a little nuts when it appears
               I'm only person who thinks the acoustic chamber of an acoustic guitar amplifies sound...
                                 so forgive me if I sound a bit defensive. ;o)
         

Sorry, but the chamber does not amplify, at least not in the sense that an electric amp amplifies an electric guitar.

The chamber serves to capture and direct the sound energy.  But if you were to compare the sound of strings (with no chamber) an inch away from your ear to what you hear standing a few feet away from the chamber of the acoustic guitar, you would not find the chamber to be louder.  Therefore, no amplification, just efficient capture and redirection.

[The Observer]

...

[The Observer]

Utilitarian,

You state the chamber does not amplify sound.

     I gather you think sound is being reflected back to the front of the guitar,
     constructively interferes with the string's waves going forward,
     and hense a louder sound.
   
     And that there is less sound behind the guitar because of reflection.

I will state that you are entirely wrong if this is your interpretation.  (please see attachment)

You first need to understand what a Helmholtz Resonator is...
  Then ask your self how resonant systems store Energy.
    Finally, you will realize why Tesla, Stan and others were/are using Resonance on a daily basis.

                                           The Observer

[mondrasek]

When a guitar string is plucked, a finite amount of energy is imparted to that string.  That energy is then dissipated in several ways.

Mainly, you notice that the string will vibrate at it's natural frequency.  This vibration creates sound waves in the air surrounding the string that radiate outward, similar to the way light waves radiate from a light bulb.  Only a small portion of the entire amount of energy initial imparted to the string is imparted to each sound wave (each vibration cycle).  And only a fraction of each sound wave (radiating 360 degrees from the string) is going to reach your ear.  The further from the string you are, the smaller still the amount of each sound wave that your ear will receive.  This is why the sound is less loud the further away you are, exactly how a light appears dimmer the further from it you are.

In an acoustic guitar a large portion of the sound waves facing the acoustic chamber interact with it in several ways, localizing it, and therefore not dissipating into the air further away.  First, the sound waves may reflect and bounce around in the chamber, and ultimately be re-directed towards the front of the guitar through the opening as constructive interference.  Secondly, the sound waves cause the wood of the acoustic chamber, and especially the top sounding board, to vibrate at the same and harmonics of the same natural frequency, again, localizing the sound energy rather than letting it dissipate into the surrounding air.  The vibration of the sounding board also constructively reinforces the vibration of the string both acoustically (through the air) and physically (through the bridge).

The second, and often overlooked, way that energy is dissipated from the string is by energy transfer from the vibrating string through the bridge, directly to the sounding board of the acoustic chamber.  That energy is also localized and vibrates the wood of the sounding board adding to the constructive reinforcing interference and subsequent increase in heard volume of the struck note.

These are all reasons why the size, shape, thickness, and material choices for the acoustic chamber, bridge, and especially the sounding board are important to achieve an acoustic guitar with particular "tone" as well as volume.  It all has to do with how much of the energy from the initial plucking of a string is imparted to these constructive interference sound wave producing elements.  Any energy lost to dampening materials or through the air not directed to your ear is energy not perceived by you as sound.

An electric guitar lacks most all of the constructive interference sound wave producing elements of the acoustic guitar.  Instead, it is designed to keep the energy in the string itself.  These strings are thinner, stiffer, and looser.  They are designed to vibrate with a smaller amplitude than their thicker, softer, tighter acoustic counterparts.  This causes less of the energy caused by plucking to be imparted to the air as sound, for sound is just a loss since it is not the method by which energy is transferred to electric guitar pickups.  The electric guitar string is also often ended at a heavy nut and bridge that are designed to keep the energy in the string, not transmit it to a sounding board.  You can notice this effect as more natural sustain in electric guitars with heavier nuts and bridges/tailstocks.  Likewise, the frets on the electric are also usually much heavier than on an acoustic so as to transfer less energy to the wood of the neck and keep it in the string.

The electric guitar pickup includes a magnetic field that resists the vibration of the string and unfortunately dampens it somewhat.  This additional loss mechanism is not present on the acoustic guitar.

If you string an acoustic guitar with the thinner, looser strings of an electric, and dampen the constructive  interference sound creating properties of the acoustic chamber (mainly the sounding board) by attaching a heavy weight, thickening it, etc, it's volume will decrease immensely.   Eliminate the hole so that sound cannot enter or reflect back from the chamber and I believe you will be down to the volume of a similarly gauge string electric.

Likewise, take a well built electric with a heavy (brass) nut and bridge through an amp turned up to the same volume as the best acoustic, and I guarantee you it will ring the notes for longer.  The electric guitar strings can vibrate for a longer time since the initial energy is not transferred to other acoustic elements directly.  They are just not optimized (like the body is not optimized) for producing sound directly.

M.