THE DUMPSTER DRUM
I receive email from all over, on many topics. I received one from a friend (who is an amateur luthier and repairman) that was completely charming, and that made a point about how guitars function. I thought it would be fun to include it as I received it, without changes or editing:
I had a wonderful a-hah! moment, and it startled me greatly. I was so enthralled at the time, I didn't think to take pictures, so I hope my words will be enough to convince you, or, at least give you enough clues to make up your own mind.
We went with friends to the new strip-mall built outside of town. I went scavenging around the back, being that kind of dude that is always looking for treasures left behind, like some cargo-cult islander, a stranger in a strange land.
Near the little tin hut that houses cardboard, later to be crushed and bundled was a strange box, so I opened it to look. Inside was something I had never seen before: a plastic brown disposable keg, made like a big coke bottle, but much larger, about 4-5 gallons, with a heavy-duty cap & a siphon to the bottom.
In volume, it was about the same as a dreadnaught acoustic. It had a very thin skin, but the cap was industrial.
Of course I didn't know anything about it, & was frustrated like a chimp because I could not unscrew the cap. I knew that if I took it back to my wife & the friends that were eating & schmoozing, they would not want me to keep it.
I started to finger-drum it like a drum. It had the most amazing acoustic response. I just could not believe my ears & hands because it literally bounced with my fingers & made the loudest sound I ever got from any plastic bottle of any size. It was a wonderful drum. Because it was so wonderful I was determined to keep this strong drum.
So, I had my pocketknife, & I began to dis-assemble the cap guards so that it would be able to be all mine, minus the siphon. As I began to cut the locks on the cap, a tremendous amount of CO2 gas began leaking out…not for just a few seconds, but for a long long time. This plastic bottle was under such great pressure, I got surprised. I had to cut about 9 plastic safety locks, & even though I had done 2/3 of them, & the cap got looser, more gas kept on coming out.
It was under a lot of pressure, & that kept the skin of the plastic alive & responsive. As soon as all the gas came out, & I removed the siphon, it was all as loose as a... as an old man's scrotum after 3 hours in a steam room. In polite terms, as loose as a big balloon that had once been tight, but had all the helium taken out... or even air, if you will. At that moment, I was sad that I had lost my drum, but happy to just discard the now flaccid jug in the garbage, where it now belonged.
Which led me to fantasize that perhaps, in an analogous way, the braced system of a guitar gives the skin a similar "personality" —as if it were (in its own way) "pressurized." Perhaps there is a better word, but for an example of the difference between responsive & non-responsive, I could not imagine better.
Thinking of You. Enjoying your books, of course. Someday I will do things. Progress is my most important product, elusive as it may be.
Your garbage-bandit friend,
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Alan is right about pressure, tightness, and tympanicity (tympanic means being bell-like and/or resonant, particularly as a capacity of a stretched membrane). I'd interpret the "personality of the skin" thing a bit differently, though. A guitar, like the dumpster-drum he describes, functions in the most lively way when the "skin" is taut and tight. Ideally, the skin is pushed to the breaking point. That brings us to the traditional Spanish-guitar making adage that the best guitars are built "on the cusp of disaster" (i.e., just strong enough to hold together).
Alan is essentially describing a guitar with a thin top that is held taut by the pull of the strings; that's what gives the skin its tympanicity – i.e., its resonance or capacity for resonance. The braces are there to keep the thing from falling apart or exploding, and to give an organized shape to its vibrating actions. Once the tightness is gone, so is the tympanicity.
Overbuilt guitars don't have tight tops. They have overstrong and overstiff tops that easily resist the pull of the strings. The top isn't... uh... pulled tight and struggling. In fact, it's the other way around: the top is unyielding and the strings are struggling to move it.