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Compressed Air Guitar

Denser air for thicker sound?
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A reinforced acoustic guitar with a speaker-type membrane in place of the sound hole.

The air in the guitar would be compressed for a greater volume of air, driving the speaker for a louder if not unique sound.

No more dropping a pick in the guitar either.

Giblet, Apr 10 2005

atmosphere effects on pitch http://online.physi...POM_Final_Paper.pdf
Yes, it seems that the atmospheric gas would effect the the pitch. [siwel, Oct 30 2005]

[link]






       Sure, why not?
whippinggas, Apr 10 2005
  

       wouldnt it mess up the sound ... i thot the hole is the soul of how the guitar sound works... not sure though. Like the pick not dropping thing thou... thats a pain !!
halfbloke, Apr 10 2005
  

       Would that be a greater volume of air?
bristolz, Apr 10 2005
  

       The air would not be able to move freely. Thus, you might as well fill the guitar with anything, like custard, or something more solid perhaps, like wood. You'd get the opposite of a louder sound, and you'd be halfway to having to reinvent the electric guitar all over again.
Ian Tindale, Apr 10 2005
  

       I had started to give this a bun, but then I realized there was an actual guitar involved.
ato_de, Apr 10 2005
  

       Wouldn't the speaker membrane give the air the ability to move freely as it is sprung and has play? Or is the air in a sealed speaker box impervious to motion?   

       In a sealed speaker the speaker cone moving compreses the air inside, would not the opposite happen if the air was moved via the springs against a speaker?   

       I thought of filling the guitar with custard as well, but the weight would be rather compromised, plus any Hendrix style smashing would be far too messy.   

       If my membrane thingy was tuned to the volume of compressed air in the guitar against the sound of the guitar uncompressed, wouldn't it work rather well?   

       I'm no Batman ("Batman was a scientist" - HJS) but this seems to make sense. Am I missing something fundamental?
Giblet, Apr 10 2005
  

       Yes you are. The soundboard on the guitar vibrates the air in it. Putting anything more dense in there would kill/eliminate the sound.
lowbot, Apr 10 2005
  

       So why wouldn't the sound board compress the air, transmittig that compresison to the speaker cone on the front, thus compressing the air outside the guitar, making sound?
Giblet, Apr 10 2005
  

       Okay. The soundboard vibration generates very very little energy. If you put something more dense than room air in that hole you will need more energy to vibrate that mass to produce the same amount of sound.   

       Like someone said above, youre a cognitive step away from the electric guitar which can push air around more effectively with electric speakers.
lowbot, Apr 10 2005
  

       Sorry, [Giblet], this just wouldn't work. The soundboard (properly called the 'table') can only transmit the strings' vibrations accurately and efficiently if it is free to move. An enclosed space behind it compromises this freedom. The table will be less able to move backwards than forwards, and the sound would be distorted. If the air in the space is compressed, this situation is made even worse.
//wouldn't the sound board compress the air, transmitting that compression to the speaker cone//
No, because the air would damp the vibrations of the table, and the cone would further damp the vibrations of the air. You'd be better off letting the table freely move the whole mass of air inside the body, which is, of course, what actually happens. The most articulate acoustic tone comes from an instrument with a very delicate structure. Some lutes actually tremble when just sitting there.
The situation with a sealed loudspeaker enclosure is somewhat different, and depends on exactly what you mean by 'sealed'. You might want to look up 'acoustic suspension', 'tuned enclosure' and 'infinite baffle' for some details.
angel, Apr 11 2005
  

       //Don't resonator guitars work on this sort of principle//
Resonator guitars (Dobro, National, etc) have the bridge mounted on the metal resonator plate, which is suspended flexibly on the body; it functions in the same way as the table of a regular guitar, while the body has relatively little effect on the sound.
angel, Apr 11 2005
  

       If putting compressed (dense) air makes it vibrate less, why not put helium in the guitar?
siwel, Oct 22 2005
  

       Listen to the [angel], this won't really help things any. Although I'm sure enough people out there would buy one so long as it was painted sunburst and went twang.
wagster, Oct 22 2005
  

       [siwel]: It doesn't matter what gas you put in there; what matters is that it's unable to vibrate freely (that is, along with the exterior).
angel, Oct 23 2005
  

       [angel][wagster] My annotation was a bit tounge-in-cheek. In reality, putting helium in would have very little effect on the volume. It might improve the sustain slightly because of decreased damping. The major difference would be that it would be slightly sharper for the same string tension. Frenquency of vibration increases with spring rate and decreases with moving mass (actually, the square root of the ratio). As [angel] pointed out, the air in the box is part of the moving mass. A helium filled guitar would have to have longer strings, lower tension, or heavier strings to be in tune. Of couse, sealing the hole to keep the helium in would really goof everything up.
siwel, Oct 29 2005
  

       Just to add a dumb question: How about adding a horn ala old gramaphones or "hearing trumpets" just behind the strings? There must be a reason why this isn't done, but I can't visualize what that reason is.
James Newton, Oct 29 2005
  

       //A helium filled guitar would have to have longer strings, lower tension, or heavier strings to be in tune.//
No, it wouldn't. The pitch of a sound produced by a guitar (or other stringed instrument) is determined by the tension, weight and vibrating length of the string. That's all. Resonances in the body (including any contents and attachments) affect the timbre and the volume, but not the pitch.
[James Newton]: That's effectively what the resonator guitars do (Dobro, National Resophonic, etc). The horn on a gramophone amplifies the small vibrations of the needle, which is connected to a diaphragm at the narrow end. The plate or cone of a resonator guitar amplifies the vibrations of the strings passing over the bridge which sits near the centre of the plate.
angel, Oct 29 2005
  

       [angel] I'm a better engineer than a musician. Don't take my word for it. See the link I posted above. The gas inside the guitar vibrates with the body and would be subject to all those beautiful equations.
siwel, Oct 30 2005
  

       I'm surprised that, as an engineer, you're misunderstanding. A helium-filled guitar would certainly sound different from an air-filled guitar because it would resonate differently, just as my basswood-bodied Casio guitar sounds different from my acrylic-bodied AXL or my maple-bodied Burns or my mahogany-bodied Epiphone; the materials have different densities so they have different effects on the sound. What they do *not* do is alter the fundamental frequency of the vibrating string. If the sound were reaching my ear solely through the material of the body, or if the body were the principal vibrating component, matters would be different, but the density of the guitar body does not alter the pitch of the notes that it produces.
angel, Oct 30 2005
  

       [angel] Rather than argue fruitlessly about this, I have a guitar, a frequency analyzer, and some helium in my lab at work. I propose is that I cover the hole with Saran wrap, pluck a note to measure the frequency, then fill the body with helium and try it again. I'm travelling this month, so it will likely be close to December before I can try this. I'll send a recording. If there is no measureable difference, I will publically conceed. I've got some argon too, which is denser. I might give that a shot while I'm at it.
siwel, Oct 30 2005
  

       //A helium filled guitar would have to have longer strings, lower tension, or heavier strings to be in tune.// I disagree, it would merely alter the tone which is determined by which harmonics resonate in the body. The fundamental frequency of the note is determined by the length, weight and tension of the string, this will remain constant even if there is no body on the guitar at all.   

       However, I would just *love* to hear what a helium filled guitar sounds like, and argon too. If you get around to this, please could you post wav or high quality mp3 files, and frequency graphs if you can get them. It's a fascinating project.
wagster, Oct 30 2005
  
      
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