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

[The Observer]

Swimmingcat,

First, welcome to the forum, cool name.
I am honored that you felt compelled enough to answer my question to sign up.

Second, thanks for spending the time to write a clear answer.

Third, I can tell you made a lot of your theories up and do not play acoustic guitar..
   
      Basically, you are saying that sound that would have gone behind the guitar is refocused (echoed) back to the front... and constructively interferes with the strings waves to make bigger waves on the front side and virtually no wave on the the back.

     Thus your explanation for louder sound with no extra energy.

     You mention Resonance. but do not account for it.

Although the statement, "the acoustic guitar is loudest near the hole" is true...
    It is also louder everywhere, including behind the guitar.
        As a person who has played for over 30 years, you will have to take my word for it.

You mention a loud speaker.
    You will be surprised to find out that I claim a loudspeaker is an overunity device !
        The reason is not as simple as this (the guitar)... as one must understand magnetic permeability
                 and comprehend that a speaker built using only coils takes far more energy
                       than using a magnet and a coil/wrapped around iron.

     Anyways, since you mention resonance but do not explain how it fits into the equation...
               I will offer a short explanation.

                   You need to understand what Forced Resonance is.

          a. Every object has a natural frequency(s) that it will vibrate at.
          b. One vibrating object can start another object vibrating (must use natural frequency).
          c. A small driving force can cause a large oscillation in the second object.
              This is because of the phenomenon that Resonant Systems STORE energy.
          d. The second object interacts with the real world in terms of the energy STORED.

In the case of the Acoustic Guitar.

         There are 2 objects...

         1. the string
         2. the air in the guitar

         The String (1.) is the small driving force mentioned above.
         The Air (2.) is the Resonant System that Absorbs Energy and has large oscillations.
         You and me are the real world that hears the result of a Vibrating Systems
                                         interacting with the world in terms of the Energy It Stored.

I will apologize for acting like a know it all... but you will find all this (and more cunundrums)
      in a regular college physics text book.

The Observer

[swimmingcat]

I do not agree than a guitar or a loud speaker are over unity devices. They simply are efficient at producing sounds that the human ear responds to with the input energy (strumming or electrical signals respectively) provided. I would like to believe that they are over-unity, but your points are not able to provide enough sway.

Though I do have an open mind to over unity devices, they appear to be much like sasquashes - people have reported seeing them and there are even videos but none are available for close inspection. Without the scrutiny of others these stories just appear to be fanciful tales.

I challenge anybody to produce a set of plans for an over-unity device. I have access to a machines shop and an electronic technician. I can have it built - no problem.

The fact is that nobody can come up with such plans. All reportedly over-unity devices are shrouded in secrecy and all reports of their operation are uncorroborated - basically hear-say. I challenge anybody to provide me with an opportunity to examine an over-unity device or produce some plans to build one. I expect I will be waiting for a long long time.

Typical of the over-unit fair are documents like the MEG-patent:

http://www.cheniere.org/references/MEG_Patent.pdf

This document fails to give enough information to build a machine. It merely gives the inventors the right to take somebody to court who they think may have infringed on this patent. And if you find it confusing perhaps you could buy one of the dozen or so books ADVERTISED in the patent that supposedly explain the principles involved. I would put forward the notion that the intent of this document is to sell books.

One such book "The Final Secret of Free Energy" talks all around the subject with analogies. But the text never actually reveals any real physical phenomenon that demonstrate the principles. Where's the beef?

If the MEG actually worked and is really just a configuration of magnets, wire, and electronics then then far more money could be made by selling these machines than by selling books. Far more benefit to humanity could be gained by making small versions of this machine available to one and all to prove the concept to the world. And I would be happy to build them for the inventors to sell. They have a patent after all, and certainly would be entitled to royalties. But for some reason they prefer to sell books.
 

[Paul-R]

What we need is a truly standard strum.

How about the "gizmo" used by Godley and Creme?
http://14.media.tumblr.com/PwCIEKd8Nm7mbw05kyEUJkdFo1_500.jpg

I think it was some sort of rotating arrangement of six shaving brushes
which stroked the strings, and gave infinite sustain. Then a microphone can record the actual sound level produced.

Don't forget to include a National guitar with the steel whatchamecallit
Paul.

[ATT]

Step 1.          Realize a resonant system STORES energy.
Step 2.          Realize a resonant system can emanate energy.
Step 3.          Realize the energy emanated has to do with the energy stored.

.
With string instruments, the materials they're made of don't -store- energy, they -react- to energy (well, they store energy to 'burn' maybe).

OK, take a Les Paul, unplugged: Why doesn't it project much sound? Because the chunk of wood the strings are attached to requires a lot more energy than a vibrating string to move/vibrate much (the solid-body has a lot of 'inertia' to overcome).

Next, take a Martin D-28: Same string produces great sound. Why? because the
-thin- top/back/sides vibrate -more- with a lot -less- energy input (a lot less 'inertia' to overcome).

Moving right along, you take a 5-string banjo that uses a drum-head as a sound-board (less inertia, yet) and it's even -louder-.

The vibrations of the strings are transmitted, through both the 'nut' and the 'bridge', to the body of the guitar, the more the body reacts (vibrates), the more air is set into motion and the greater the SPL (sound pressure level).

Regardless of any sympathetic vibrations or standing-waves setup through various resonances that result from the selection and consistency of the materials chosen or their configuration in the instrument (which has more to do with 'timbre'), the primary reason for differing sound pressure levels is the relative degree of inertia between the two styles of guitar construction.

The easier it is to get the sound-board moving, the more air you're gonna push, the more volume you're gonna get.

If you want to get into phasing, standing waves and harmonics, that's also an interesting direction that will lead you more into tone than to SPL, but the original question about 'why' is one -louder- than the other follows the above tenets (at least with guitars, winds and brass are different animals).

Tony
.

[ATT]

@Observer
You know, I don't necessarily disagree with the direction you seem to be taking with this thread because it is interesting stuff to ponder, but it would also be useful to run some practical bench-tests and gather a little data to mull over.

How much energy would you expend in intitiating the 'seed' vibration?
How much of the resulting SPL could you 'direct' twords a collector?
Upon collection, what means would you use to convert SPL to, say, electricity?
Compare converted-energy to initiating-energy and see if it still seems viable.

I've used an old Audio Cyclopedia (Howard Tremaine) for years (since '72) as a reference for sound, the 2nd edition of this volume is still available; ISBN 0672206757, if you're more interested in sound than the average guy.

There's been a fair amount of work done in piezo-acoustics for energy production/conversion, too, you may find some interesting directions to follow there, as well.

Tony