estebanana -> RE: Harmonic questions? (Aug. 31 2017 2:15:18)
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quote:
I have 2 "technical" questions. - If I play my guitar on the 12th fret. I recognized that the A string, drops suddenly down in volume very steep and completely dies out in 2 seconds. The other strings gradually decrease in 5/6 seconds. Why? - I tried in a store a blanca (great service in the shop/great guitar). However, playing the D string, 2nd fret (a minor chord) I believed that every time there was some dis-harmonic in the background which annoyed me tremendously. Obviously it was no normal string buzz nor where it the string ends rattling on the front. But like there was a small ringing in the background. When the sales guy played, it was gone. But he had a more gentle classical guitar playing style. Any thoughts what this is? The question is why are you playing the A string on the 12th fret? The answer is really, who cares? Is there a solea accompaniment falseta you need that must have that particular note? Probably not. So no one really owes you a free answer, basically, because if the guitar otherwise plays well, who cares? The answer is complicated, but it boils down to this, the high partials are built ona platform of intonation that is made of compounded errors. The guitar intonation system is not perfect, so in conjunction with a myriad body modes and resonances, an imperfect system of compounded intonation error creates odd harmonic phenomena. The only way to understand why your particular guitar does that particular kind of harmonic stuff on the high frets is to have it in person and look at the intonation carefully. Usually the the basic reason a string dies out at the 12th fret is because the saddle is not in the right place and this sets up some other overtone phase cancellation that is hard to pinpoint, unless you actually have the guitar and can unravel it with the right sound analysis program. So the answer is take it to a guitar maker who is deep into computer analysis of high partial effects and pay them to spend 90 minutes with the guitar. If the guitar does not burp and fart, or otherwise have cross phase overtone or distracting overtone activity in the root positions then you're good to go. If you can play the open A string and it does not fart, or barf, then why are you fussing with the 12th fret? Asking people to sort out an upper partial phenomena without the guitar and being able to check saddle intonation first is not really fair. It's a hands on business, guitar making, and solving problems in the abstract is not practical or maybe even possible without collecting data on the instrument in person. I doubt very seriously you'll get an answer off the internet. I speculate that it is possible on guitars that have main top resonance that is on the note A, that the A can cause in concert with intonation cumulative error, havoc on the guitar in several places. That is why we as makers back away from making guitars with main top rez up near A. It's death for flamenco guitars in general so we stay in the vetted zone of F through almost G and maybe hazard G#, but square on A is generally not helpful. Of course without having the guitar it's near impossible to tell, unless you know how to evaluate and understand the difference between main air resonance and various modes of top and back. To get even more esoteric, the back resonance could also be a culprit and causing weird cancellation, but again an analysis of where the main back mode is in relation to the top is important to establish and that means having the guitar in person. If the main back mode is too close to the main top mode, trouble. So really asking why your A string is taking a dive at the 12th fret is not a practical matter unless you need that note. And establishing a firm notion as to why it happens would take a mode saavy maker several minutes if not a half hour to parse out, with the guitar in person.
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