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When you strum the strings on an archtop, the noise, the end result, begins with vibrations on the strings.
What is the pathway that the energy takes to create energy/sound on the guitar's body top? Is there any evidence or measurement methods available?
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12-31-2014 11:31 AM
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Well the string ends being anchored at the fret and tailpiece ends, the energy has a downward (and lateral) movement that is kinetically transferred to the bridge. The initial attack is into the top itself, but the tonal quality of the guitar is actually a complex set of contributions from the coupled back (if it's built well, tuned correctly and the back is sufficiently compliant) and the Helmholtz air resonance, a standing wave resonance, inside the body of the guitar. These are the primary contributors to the acoustic sound we hear, and the feedback and balance between them are what makes the acoustic character of the note's decay.
There's been a bit of this written by members of the Catgut Acoustical Society when they were in existence, and luthier Alan Carruth is one of the more knowledgeable authorities on archtop guitar acoustics. The radiating efficiency of a top is dependent on a good coupling between the resonant signature of the top and back.
I don't know if this answers your question; but there's much more. Arthur Benade's book The Violin as a Circuit (I think it's Art's book) looks at string driven acoustic systems, mostly violins but there's been a bit written about flat top guitars and archtops, all of which have differing dynamics of energy transfer and capacitance. There was also a lot being done at the University of Sydney and Bell Labs along the lines of free plate contributions and holographic imaging in regards to acoustics. MIT had some great finite element analyses on guitars too.
That's what I can think of off the top of my head.
DavidLast edited by TH; 12-31-2014 at 12:18 PM.
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Here are two links. have fun. Then you incorporate pickups into the equation.
Dr. Russell's Research - Acoustics of Guitars
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Hi David and Rob,
I did post a response last night but it has vanished with the New Year! First off my background is in medical science not physics so I am an acoustic Luddite.
I've tried guitar book material but it tends to be anecdotal. I don't currently have university library access so I didn't want to be buying research papers speculatively. I appreciate that there is probably more info available on orchestral stringed instruments rather than guitar.
I'm interested in the energy transfer at the nut, fretted note, the bridge and string anchor points and then the factors affecting and a description of body vibration.
I would also like to get my head around flat tops v arched tops, bridge type influence and sound hole shape, size, presence/absence.
Many thanks
Pete
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Some introductory reading, and there've been some good articles in Scientific American over the years.
http://www.oberlinacoustics.net/arti...nstruments.pdf
http://www.logosfoundation.org/kursu...nstruments.pdf
Just skim over the greek letters and you can get a good idea of some really interesting things to be aware of in your guitar. Learning about the physics of the instrument was really helpful as a builder and as a player.
This'd make an interesting discussion thread.
David
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Thanks, David! I'm looking to this thread.
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Hey, how many acoustic researchers/luthiers are in this group? I think it'd be fun to have a group here to talk about, discuss, throw around opinions and debate issues of acoustical research. I've begun working with another luthier and it's really interesting how much mystery shrouds the urge to experiment. I've had the great luxury of studying and working with acoustical engineers who happen to be great luthiers and using fast fourier transforms and glitter pattern frequency analysis, we are able to not only determine a really good thickness for tops and backs, but we've been able to fine tune resonant peaks through thicknessing, bracing and coming up with new bracing patterns that increase efficiency, alter the overtone signatures of the guitar.
But I've also found it controversial and a lot of people see using scientific methods as counter to the religion of magical and artful lutherie. I think there's plenty of room for art when fear of the unknown is assuaged by quantifiable knowledge. But the art and theory duality is alive and well all over the guitar world. It could be an interesting thread.
Anybody here build and experiment with plate tuning?
David
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I think that makes sense David, the whole notion that lutherie is some unknowable dark art doesn't promote the end user really understanding what features would benefit them in a guitar.
Originally Posted by TruthHertz
The Catgut Acoustical Society has yearly PDF files with information and research for stringed instruments.
Guide to the Catgut Acoustical Society Newsletter and Journal MUS.1000
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Don't mean a thing if ain't got that SING!
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Hey David, I wouldn't call myself a builder much less a luthier, but I'm working on my first archtop and I'm very interested in all of this sort of stuff. You'll find the methods quite rough, but I'm documenting the process here: Originally Posted by TruthHertz
https://www.jazzguitar.be/forum/guita...70-begins.html
You gave me some good info over PM a while back regarding traditional arching patterns. I won't likely have anything valuable to contribute to this thread, but I look forward to soaking up what the more experienced have to say.
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Ohhh yeah! I remember now. Yeah that's great! How's the graduation going? Just checked out your thread, it looks really great. High tall arching I see. I've gone a different direction, myself. Building flat tops that can reasonably produce the frequency signature of an archtop. Bracing design in flat tops is a really overlooked science. But maybe I should wait and make another thread for these discussions. Originally Posted by Jehu
I'm going to follow your progress with a great deal of interest. Very nice.
David
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One of my very favorite subjects! Originally Posted by TruthHertz
I've commissioned two completely acoustic arch top guitars in the last 4 years. Each one is tonally different from the other, and arrive at their sound through variations of top design.
The first guitar is 17" x 3", x-braced, f-holes, with a 25" scale, made from European spruce/European maple. The luthier carved very high arches in both the top and back, yielding a large inner body cavity. The guitar has a beautiful, very complex tone, emphasizing the midrange.
The second guitar is 18" x 3 1/4", x-braced, sound port, with a 25 1/2" scale, made from European spruce/European maple. The target sound for this guitar was a combination arch top/flat top. We decided that sound ports would disrupt sound transmission less, and moved the holes to the upper treble bout, leaving the lower bout soundboard free to work from edge to edge. The top was carved much flatter and thinner, producing a very resonant and responsive guitar, with a deep bass tone.
It amazes me what a good luthier can produce. I love each guitar, and especially enjoy their differences. J W Murphy Guitars built both instruments.
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It's going well so far, but I don't know what it will sound like quite yet! As you can see I have both the body and neck close to completed. We'll see: I may do a little further tuning to the recurve of the back once I have the neck attached, but I think the top is what it is at this point. It'll be fun to start on the next one and fiddle around with things. Originally Posted by TruthHertz
I'd be very interested in checking out your flat top builds, if you're willing to share. It probably deserves a thread of its own.
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The plates are bound at this point? Glued to the ribs? Maybe we can discuss some techniques for checking the resonances, make sure you're not building in any dead spots of wolf notes. Yeah the flats are being prototyped right now. Some very promising nylon string developments for a nylon with a 14 fret steel spaced jazz guitar. Totally new bracing system for the 14 frets. On the third prototype and each gets better. Almost ready for production. Something never done before: a nylon that's fast, tight and has the expression of a classical but the snappy attack of a steel. Sure I'll share the designs when it's where I want it to be. Originally Posted by Jehu
It's so much fun to play, really easy on the hands. I can't put it down.
Tuning backs and tops on a flat top is also turning out to be an incredible technique. More later though.
David
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So much variation and possibility lies in the art of arching and tuning. I studied with violin builders, Cello and Gamba luthiers and it's amazing how the curve of the arching effects things like attack response, sustain, the character of the decay and the way we hear that instrument. And that's even before tuning. Originally Posted by Rick Kay
An luthier with a command of the parameters of the wood and air can do so much. It takes a lot of time and understanding to master the craft, make it an art. A lot of luthiers out there, only a few masters.
I found that for the field at large, hype and marketing are more important and more time consuming than even building and experimenting with the actual instruments. That's why I thought a luthiers' thread might be kinda fun. Not to sell guitars but to share ideas.
The man I worked with had an interesting visitor one day. This player brought in two guitars that were built by a well known luthier. The first one was an attempt at a clear high end for which it succeeded, at the cost of any convincing bass. In an attempt to remedy that situation, the player commissioned a second, which had more bass, but the treble was not clear. "That's the way I build them, that's my sound" the luthier said.
He brought them to A and said "I hear you're good at getting the most out of an instrument. Will you fix these? Put this bass into that, and make that one play treble like this?" And he did. But in the end it was not worth his time, but he enjoyed the challenge. He never got a commission out of the guy either. That's the luthier world.
We play these instruments, worship the curves and seek out the builders like sacred beings. But in the end, it's wood and the people that understand it. It's like wood jazz in that way.
David
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When designing the second arch top, the 18", Jim Murphy and I had lengthy discussions about sound transmission and sound hole placement. Here's part of a discussion about lateral sound transmission across the soundboard, in regard to "f" holes:
"The young's modulus is a measure of stress over strain, describing
the amount of stress (force/area) needed to deform a given material. The
higher the value of the modulus, the stiffer the material is. It gets really
interesting when the varying stiffness of the different parts gets thrown
into the mix. It is commonplace to see the wood grain treated as a
traditional composite material, like carbon fiber. These composites are
divided into two types of materials, the fiber (stiff, structural
components) and the matrix (softer phase that holds the fibers in place). In
carbon fiber composites, the matrix is typically an epoxy resin, and the
fibers are...well, carbon fibers. With wood, the slower growth acts as the
"fiber" while the soft spring growth acts as the matrix. The young's modulus
along the longitudinal direction (with the grain) can be calculated by
multiplying the modulus value of each component by its volume fraction and
adding them together. Interestingly enough, this is not the case through the
grain (transverse direction). Going through the grain, the modulus is mainly
controlled by the more elastic "matrix" phase (i.e. the weakest link in the
chain). Additionally, the quality of the bond between the hard and soft
grain components also plays a large role in the stiffness across the grains.
Given the largely vertical shape of the traditional f-hole it would
definitely interrupt the vibration transfer through the softer, more
elastic, transverse direction. It would seem that the stiffer the wood gets,
the higher the efficiency of vibration transfer, leading to a louder/faster
output from the guitar. In terms of warmth and sustain, it would seem
necessary to decrease the transverse modulus while retaining a reasonably
high longitudinal modulus for structural reasons (potentially making one
lean towards conifers for top materials). However, volume fraction (grain
spacing) also plays a large role in determining these modulus values, and it
varies widely between different materials and growth conditions (old growth
vs. new growth, etc...).
I guess this is where the "art" portion begins..."
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Yep, we're nearing the end game on this build. The box is closed, bindings installed, recurve carved. Now I'm just fiddling with the neck joint. Originally Posted by TruthHertz
But this definitely won't be the last, so I'd love to hear your insights!
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