Official Luthiers Forum!

The other thing to consider is that the applet you have been looking at is a 2 dimensional representation of the 3 dimensional motion of the string.
and is based on fixed end points(rather than having a saddle which is able to move vertically)
It's a great tool for understanding string motion in response to different pluck locations
You might perceive the action of plucking the string as parallel to the soundboard but there is a perpendicular component too and even if you were able to initiate the motion in a pure parallel direction, the string motion quicky resolves to a 3 dimensional action.

http://youtu.be/6sgI7S_G-XI

Slow motion vibrating strings.

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Old growth, shmold growth!

No worries. Spread the word!

There's a couple of chapters in the Design volume which are very mathematical. I wrote it like that because I'd read too much unsubstantiated opinion and didn't want to add to it. It was basically an invitation for people to challenge what I was saying, but to do so would mean them supplying an alternative with substantial and quantifiable argument behind it. If someone does, well and good! Those sections are summarised in layman's terms so you don't need to be a maths major to understand and use the concepts. My co-author is not mathematically inclined, so it had to pass his "understandability" test.

Here's some more slow waves:

http://www.acoustics.salford.ac.uk/fesc ... rvideo.htm

Lot's of interesting stuff on that site.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

So I've modified my perception such that if anyone asks my opinion on how the strings interract with top I will tell them that the directional forces of the string move the top of the guitar by pulling the bridge/saddle assembly in whatever the direction the directional forces of the vibration move it, resolving to an up down motion of the entire top as the dominant driver of sound.

Interestingly enough, I still think that if the structure is just strong enough to hold the static tension of the string and no more, it will be responsive to the slightest tug of the string on the bridge/saddle assembly. To me, the strength to weight ratio of the top materials has become even more important, especially for nylon strings. Not so sure about the tapping thing.

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Old growth, shmold growth!

Yes, the bridge bounces up and down when the top is vibrating in the monopole mode.......the virating mode that is the largest sound producer.

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Formerly known as Adaboy.......

Thanks, Trevor, for the details on steel strings' transverse/longitudinal force change ratios -- good to know.

Great to see the progress in the string force discussion.

On minimal strength, also keep in mind the distinctions between stiffness, strength, and creep. E.g., a rubber band is fairly strong but not stiff; a glass rod is stiff but not strong; silly putty and warm plastic creep. Acoustics are governed by stiffness (and mass) distributions. We don't often see braces breaking, so strength per se is not a major problem for guitars, but long-term creep is. Creep is most likely in wood fibers that are under high stress -- stress that isn't high enough to break the brace, but is enough to deform it over time. Shaving a brace reduces its stiffness, of course, but its relative vulnerability to creep also depends on its shaved cross-section (rectangular, triangular, parabolic...). For a given amount of stiffness, a triangular cross-section has relatively high stress and is thus more prone to creep than a rectangular one (though the triangle also has slightly less mass). The brace pattern matters, too... e.g., Falcate bracing has 4 rectangular braces passing longitudinally under the bridge, which should give it relatively low stress and creep. I can start a new thread for this topic if wanted.

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David Malicky

Probably a good idea!



Yes, that's correct. It also has carbon fibre on top of the braces to further guard against cold creep.

Here's some more stuff that people may find contentious : It is very, very, very difficult to make a really responsive steel string guitar that doesn't incorporate carbon fibre in the structure. If you take out enough wood from the top to make it really responsive, it will collapse due to cold creep way too soon. A well designed bracing system incorporating CF has a monopole mobility (a measure of responsiveness) approximately 50% higher than typical wood-only braced guitars. (That's data from my measurements of monopole mobility from ~20 big and small brand name SS guitars)

Please discuss!

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

That's just wrong. Carbon fiber has no place in Lutherie! with a capital "L"!
(sorry, couldn't resist.........!)

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Old growth, shmold growth!

...but it works so very well!

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Wow, that's quite a difference! Does make sense though. You can make the top quite flexible before the bridge over-rotates right off the bat. And then cold creep is the only real problem.

Maybe I'll try laminating up some braces and peel the top off my prototyper for some experiments. I think I'll do just the X, since that's the big stress taker, and would save a lot of effort laminating for all the other braces and resharpening as they eat the chisel. Not looking forward to getting CF dust all over the place though...

I do have a tendency toward organic materials (even the common adjustable truss rod irks me a bit), but top bracing seems like one of the best places to sacrifice romance for practicality. Plus if I can get my tops to a relatively high level of creep resistance, I can use integral necks, which I like for various reasons

Trevor--I still have a couple of questions, and I appreciate the time you're taking to explain your thinking.

Question #1: If the guitar is being driven strongly at the fundamental frequency, and weekly at the frequency of the first partial, and not at any other frequencies, where are all the other audible partials coming from? Are these just the partials that our ears manufacture? Why do they persist when I damp the fundamental and first harmonic at a node of the other partials?

Question #2: How is it a "dead give away" that my ear assigns the pitch to the fundamental? Our ears will do that to any harmonic sequence, whether there is any fundamental present or not.

Here's a new thread on stiffness, strength, and creep in guitar tops, including use of carbon fiber:
viewtopic.php?f=10101&t=33703

May the Tap Tuning thread live long and prosper. Or at least have a few fewer topics.

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David Malicky

That's just wrong.
reconsider,
in the world of classical guitars it's increasing case of user of Smallman or Smallman's copy and the world prominent concert player use it..
and as We can see big part of luthier community use carbons rod in the neck

regards
fric

OK. So we don't all get very confused, we ought to agree on a nomenclature. The one that seems to have the most prevalence calls, say, 100Hz the fundamental, the first harmonic and the first partial, all meaning the exact same frequency. It starts to get confusing when you add in the first overtone, which would be at 200Hz. Consequently, I would suggest we forget about the word "overtone". For clarity, the difference between a harmonic and a partial is that a harmonic is a simple integer multiple of a fundamental whilst a partial isn't quite, but (usually) nearly is. More generally, a partial is any frequency component that makes up a more complex tone.

http://en.wikipedia.org/wiki/Harmonic_series_%28music%29#Partial.2C_harmonic.2C_fundamental.2C_inharmonicity.2C_and_overtone

Having got that out of the way, what I wrote prior was the "simple" explanation where the (unstated) simplifying assumption was that only the string's fundamental frequency was excited. Usually a lot more partials are excited too, and as the monopole can be driven over a wide frequency range, all these partials will drive the monopole simultaneously via their transverse waves. But every partial is also responsible for a (weak) tension change signal at double its frequency, which, of course, is difficult to differentiate acoustically from the octave higher partial driving the monopole. Usually, the long dipole type mode has a narrower response range and is harder to drive, so you won't hear as much of the tension change signal as you move away from the long dipole resonant frequency. I think that answers that one, but let me know if that's not clear.

The "dead give away" is that if you were able to excite only the string's fundamental, that is the frequency you'd hear from the guitar, as the monopole is driven by the transverse wave. And that is what you actually hear. If the main driving mechanism of the top was the tension change force, that force always runs at twice the fundamental frequency, so you would predominately hear a sound an octave above the string frequency, which you don't. So that's the "dead give away" that the transverse wave "pumping" the top is the predominant drive mechanism. Again, if that's not clear, get back and I'll have another go.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Hi Trevor,

Very interesting stuff and debate so far going on here. Are the "typical" wood-only braced guitars you refer to above the ones that you cite in your paper to the 61st Meeting Acoustical Society of America in May - Taylor, Martin, Gibson, Santa Cruz, Collings? If so then your 50% higher figure is not just measuring the carbon fibre impact I would suggest. A better comparison would be against the best responsive wood braced steel string instrument that you can make or a sample of individual builder made guitars. By the way I use carbon fibre extensively inside the box of my instruments but not in the top braces.

I would argue that you can make very responsive steel string guitars without going down the route of the thinnest possible tops – indeed doing this means that you won’t get the sort of complex mids and trebles that I at least seek. Responsiveness is one component only of the overall tone/timbre that makes a great guitar (Another interesting topic to start defining just what a great steel string guitar is - is it absolute or relative?). I’d contend that there’s more than enough energy available in steel strings – nylon strings are a different matter. I’d love to have you do your measurements on some of my instruments but a UK-Australia gap makes this difficult.



Try finding ways to free up the upper bout bracing from load bearing mode to tonal/timbre shaping mode. There are subtle but very important tonal benefits in these frequencies to be found there.

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Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

I'm back.

Are you capping your braces with CF or laminating them sandwich style? The pic on your site looks like sandwich style.

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

Yes. I thought that these represented a reasonable cross-section of guitars that people could relate to. Hand built "luthier" guitars (smaller sample) have a similar spread. The reason for this, I think, is that so many people aspire to build a Martin. The very best pro luthiers will be higher up the tree, of course, building all-wood guitars and maybe using improved designs etc., but I would maintain that the use of CF will always let you go further. I played a lot of guitars at the 2009 Healdsburg festival. Obviously, I didn't measure any of these, but my guess would be that the median of the Healdsburg sample would be pretty close to the median of the sample I have measured.

I was in the UK just a few weeks ago! But it's not a difficult measurement. The procedure can be found in the usual place.

Would you like to elaborate?

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

I thought scientists didn't guess but measured [Joke !!]. I'd be surprised if in terms of the way I relate to "responsive" guitars that if I played a batch of Greenfield, Klepper, Sexauer etc guitars compared to a bunch of Martin, Gibson, Santa Cruz, Taylor and Collings guitars that I would that I would say in terms of medians they were from the same sample and I suspect the makers of the first batch would feel pretty much the same and gutted if that were the case and my guess would be the opposite of yours, but hey that's guesses for you. Which hand built luthier guitars were in your measured sample that gave you the similar spread?



Yes - when I get my book written I don't know if this BBC link will work for you outside the UK but this series of pictures that Bernard Richardson presented at the same conference as you are interesting in terms of areas of top activity as you go up the frequency range, albeit on a nylon string. Have a go at using your falcate bracing with flying buttress braces and pare right down the upper tranverse brace and see what happens.

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Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

I said median of the Healdsburg sample (i.e predominantly individually hand built), not median of the makers you named! There were some fairly ordinary guitars there (all very shiny, beautifully built, very average sound/responsiveness; i.e. all tip, and no iceberg, as we say here) as well as some good sounding ones (all very shiny, beautifully built, great sound/responsiveness). But, as you point out, it was a guess. The measurement is easy enough. Have a go! "Luthier built" is no guarantee of a responsive guitar.

Yes, I saw Bernard's presentation at the ASA and visited him in the UK when I was over. On the other hand, Smallman has 3/4" ply under the upper bout! Plenty of ways to skin a cat!

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Trevor,

Going back to my main point, if you wanted to determine the impact of just the carbon fibre composite bracing on monople mobility you would make the best wooden braced guitar that you (i.e. Trevor) could make (in terms of monopole mobility) and then compare that with the best cf hybrid brace one you could make. Would you "guess" that it would still be 50%?

Nice one picking a Smallman Pretty much a wide consensus on those instruments sound amongst players

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Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

Hi Dave,

Yes, if you(I) wanted to determine just the effect of carbon fibre, you (I) could do as you say. My point however was:

What I didn't say was CF gives you a 50% improvement over any guitar. Oh, were that true!

I was actually trying to bring out a few points with this thread:

1) Typical factory guitars (even top shelf ones) fall a long way short of what's possible. There are numerous reasons for that, but that's maybe grist for another thread
2) The "typical player" has been conditioned by heavy advertising to accept these guitars as "good". This is a conspiracy against guitarists!
3) Private luthiers (for want of a better generic term) should be able to do a lot better than factories by smarter use of materials and building to acoustical tolerances, and should not be shy in demonstrating that their products are significantly better (provided, of course, that they are!)

Re: Smallman guitars; what's understood as the generic Smallman sound doesn't match my preferences; but he sells a lot of guitars for a lot of money. Can't knock that! He must be matching a lot of people's preferences. There's quite a lot you can do with a lattice guitar, though, if you want it to sound different, or more conventional, but is that the point?

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Trevor,

Yes - nice summary . . . . BUT you did say "It is very, very, very difficult to make a really responsive steel string guitar that doesn't incorporate carbon fibre in the structure" and just happened to throw in the 50% statistic. I still don't agree with that statement - and that's a fine thing as the more differing views that get shared in the guitar making community the more it will prosper and grow.

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Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

Every year at the RAM, when the new intake of guitar students arrive, we go through a process of blind listening tests of their instruments (other faculties do the same) the guitars are usually played by one of the senior post graduate students, where they play a variety of pieces to push the guitars in different styles. The listening panel is the three Professors of Guitar, some of the other faculty members and a top guitar maker (well OK it's me), any set up and string issues are taken care of first. Consistently over the last five years or so the "lattice guitars by a well known maker" have scored at or near the bottom, and one was rejected completely as being unsuitable for playing at that level. This year we rejected a non-lattice guitar by a well known US builder so it's not lattice prejudice, as I said it's blind listening. The usual criticism of the "lattice guitars by a well known maker" are that they are very one dimensioned and lack the ability of player to inject warmth for the Southern European and South American music. We also find that a lot of the students who start with "lattice guitars by a well known maker" leave playing something different. Sometimes traditional ways are traditional because they are better, or of course because they produce the sound that is accepted as the standard against which other instruments are measured.

Colin

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I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

I'm glad you put this in, because 95% of this is over my head. Thank heavens for Gerard Gilet

It would be interesting to do a sound test using an audience that didn't have a preconceived notion of what a classical guitar 'should' sound like. Like a group of kids or metalheads that had never listened to a Julian Bream record (and therefore aren't listening for the one that closest fits their expectations)...