Replies to This Discussion

Permalink Reply by Roadkill a.k.a. John Maw on July 18, 2011 at 12:58pm

Penny.

I probably react rather badly to rules. In my day job I am a photographer and teacher (adult ed.) and sometimes get students who have read about golden section or rule of thirds and think that it will make them an artist. My point is you can either see if it is right or wrong. So the rule is superfluous. If you can't see then take up market gardening instead (OK. I'm not quite that brutal). Rules are for people who can't see.

In the same way here I feel that rules are inward looking. They assume that we know. Tests are outward looking. They assume that we don't know. I'm not sure if that makes sense to anyone except me (nothing new there then).

Mr Oily.

The bracing strips were glued almost lengthwise, but at a slight angle as in this pic. I wanted them to go under the bridge to resist the string pressure, but they had to fan out a bit because of the mag pickup.

Permalink Reply by Ron "Oily" Sprague on July 18, 2011 at 1:48pm

John,

 

As my father used to say, "Stop calling me Mr! Mr. is my father!" :-)

 

Nice pic! I would guess from the construction that you are getting incredible sustain from the steel bar and the string-through. I likw the way you did the fan bracing. Is the brace on the right side of the pic in two pieces, one of them curved? Eeeennnn - ter -esss-tink.

 

I also like your "Rules" rule. But I bet it's more of a guideline (I'm a bit of a rulebreaker meself.)

 

You should see how I make beer; I break all the rules, but somehow, it ends up working to interesting effect.

Permalink Reply by Mark Bliss on July 18, 2011 at 4:15pm

Oh man, its back! I thought this thread was long gone! LOL!

Hey, its actually very interesting timing that it has popped up. And the additional comments ARE quite interesting!

Its interesting timing because the previously mentioned home made tuning fork has surfaced. (In review, my grandfather found that the piano he was teaching himself to play nearly five decades ago needed tuning and being a resourceful man decided not only that he could tune it himself, but that he could make a tuning fork for the task. Oh, and the tuning wrench too!) Well my brother delivered it to me and instead of knocking, or ringing the bell, he struck the tuning fork against something and held the base of the tuning fork to my front door, which seemed to make the entire front of my house ring...........

Another point of interest is the mention of temperament, science and engineering by oilyfool.

Few people realize the historical role and intermingling of science, math, geometry, philosophy, religion, politics and so on with musical instruments and music theory.

And the history of temperament and tuning standards alone is a fantastic example of this, and involves some of the great minds in history, including names like Isaac Newton, Kepler, Descartes, Galileo, and many more, yes even Leonardo DaVinci! Many know he imagined and invented multiple musical instruments, but may not know he was considered one of the great musicians of his time, and that he was known to be quick with the rhyme! The first rapper?

I was going to write a blog peice on this, but now that it has come up.........

Did I mention I thought this thread was dead?

 

Permalink Reply by Roadkill a.k.a. John Maw on July 18, 2011 at 9:33pm

Hi Sir Oily.

Just Oily doesn't seem to have the appropriate degree of respect and I am certainly not calling you Fool.

The righthand brace is one piece (made out of two pieces glues together) shaped to "navigate" round the mag pickup and the sound holes. As you can see from the front (pic) it needed to take an indirect route. It has to avoid the smallest and largest holes and also the screw fixing for the pickup (which is reversed so the screws don't show from the outside). Incidentally, the pickup surround is glued on, so forming part of the structure. The idea is that it replaces some strength lost by cutting out the pickup hole.

You are spot on about the sustain and I am impressed that you can tell. Of the four instruments that I have made so far this is the best sounding acoustically by a long way. On a couple of occasions I have forgotten that the amp wasn't on, possibly because the sound holes are relatively high on the box.

 

oilyfool said:

John,

 

As my father used to say, "Stop calling me Mr! Mr. is my father!" :-)

 

Nice pic! I would guess from the construction that you are getting incredible sustain from the steel bar and the string-through. I likw the way you did the fan bracing. Is the brace on the right side of the pic in two pieces, one of them curved? Eeeennnn - ter -esss-tink.

 

I also like your "Rules" rule. But I bet it's more of a guideline (I'm a bit of a rulebreaker meself.)

 

You should see how I make beer; I break all the rules, but somehow, it ends up working to interesting effect.

Permalink Reply by Roadkill a.k.a. John Maw on July 18, 2011 at 9:42pm

Hi Mark.

Just when you thought it was safe to you back into the forums......

I was intending to add a followup on my findings from working that box (the fact that it was the bracing that dramatically changed the characteristics), but then it got going again anyway. It is really only here to make sure that MichaelS has something to smile at.

I'm pleased that you and the tuning fork have been reunited.

Mark Bliss said:

Oh man, its back! I thought this thread was long gone! LOL!

Hey, its actually very interesting timing that it has popped up. And the additional comments ARE quite interesting!

Its interesting timing because the previously mentioned home made tuning fork has surfaced. (In review, my grandfather found that the piano he was teaching himself to play nearly five decades ago needed tuning and being a resourceful man decided not only that he could tune it himself, but that he could make a tuning fork for the task. Oh, and the tuning wrench too!) Well my brother delivered it to me and instead of knocking, or ringing the bell, he struck the tuning fork against something and held the base of the tuning fork to my front door, which seemed to make the entire front of my house ring...........

Another point of interest is the mention of temperament, science and engineering by oilyfool.

Few people realize the historical role and intermingling of science, math, geometry, philosophy, religion, politics and so on with musical instruments and music theory.

And the history of temperament and tuning standards alone is a fantastic example of this, and involves some of the great minds in history, including names like Isaac Newton, Kepler, Descartes, Galileo, and many more, yes even Leonardo DaVinci! Many know he imagined and invented multiple musical instruments, but may not know he was considered one of the great musicians of his time, and that he was known to be quick with the rhyme! The first rapper?

I was going to write a blog peice on this, but now that it has come up.........

Did I mention I thought this thread was dead?

 

Permalink Reply by Ron "Oily" Sprague on July 19, 2011 at 1:27pm

All,
Am sitting in my hotel room relaxing in Vancouver, BC, after a lovely walk. Just had to see how things were going on this thread, and in looking at John's internals pic, something struck me about his and my back and forth comments regarding sustain. What John has there is basically a smaller version of Les Paul's "Log," combined with Leo Fender's string- through design for the Strat. Ol' Les specifically designed The Log to increase sustain, but then he added the cutoff halves of an Epiphone guitar to create sound chambers. In addition, John's design has a rudimentary form of fan bracing as will be found on a number of semi-hollow Rickenbackers and PRS guitars, as well as some archtop D'Angelicos. And to top it off, he's got Ovation tuned upper bout sound holes! In this one guitar, he has hit on number of construction and design solutions from some of the world's best guitar builders! And he's done it without "rules!"

I'm sensing John has an innate design sense for these little CBG gitboxes; even the steel bar is like a truss rod. You, my friend, have some luthier in ya!

Permalink Reply by Roadkill a.k.a. John Maw on July 20, 2011 at 7:13am

Wow! I know that there is a huge compliment in there, but I will be Googling for a month before I understand most of it. I have no "previous" with guitars, so I don't know those instruments, but I think I had better do some research. Thanks again.

John

Permalink Reply by Mark on July 20, 2011 at 11:41am

Since this discussion was last busy, back in January, I've been doing a bit of research. So far this has just been reading up on the science and tracking down some of the relevant academic papers but hopefully in the near future I'll be doing some testing of my own.

This has led me to think there is probably some potential usefulness in the idea of testing a box by applying tuning forks to it. However I strongly believe it is not as simple as saying that 'all points which produce a strong response are acoustically good places to put the bridge'.

Given how ubiquitous guitars have become (surely one of the most widely played instruments in the world) I was surprised by how few serious researchers have done substantial published work on guitar acoustics and structural dynamics. The good news however is that although the numbers of people are small there are a handful of individuals who have become real experts. Also, there is a fair bit of research on stringed instruments more generally, some of which can contribute to our understanding of guitars.

One such person is Dr Bernard E Richardson, of Cardiff University physics department. Some of his team's work received publicity in May thanks to the BBC website (see following link).

http://www.bbc.co.uk/news/science-environment-13573631

Cardiff is not the only centre of expertise in this field but there are still not an awful lot of places doing proper science that might help to answer the problems posed by our hobby.

Now, the pretty pictures are nice but obviously there's a lot more to it than the BBC had space to deal with. In particular, it's one thing to understand how a guitar vibrates and another thing to use that knowledge to work out which features make a guitar sound good. There's work being done on that but it's very much an ongoing area. I've been mentally ingesting an awful lot of stuff and if I tried to regurgitate it here this post would go beyond it's already verbose level and into the realm of ridiculous. However I wanted to try to summarise the crucial bits as I see them.

First, the real foundation of the sound of a guitar is in *modes of vibration* - in short, the patterns or shapes in which strings and soundboard vibrate. Strings are simpler to understand - if you know anything about harmonics and standing waves in strings you're on the right track. Soundboards are much more complicated because they have an extra dimension. This is the stuff that Cardiff University's clever holograms illustrate. They're showing the different ways in which a soundboard can move when a guitar is played.

Another way of visualising or explaining modes of vibration is through Chladni diagrams ( http://en.wikipedia.org/wiki/Ernst_Chladni#Chladni_plates ) 

 

Other parts of a guitar oscillate when it is played - the back has modes like the soundboard, also the air inside oscillates (so called "Helmholtz resonance"). However it turns out that most of the sound from an acoustic guitar comes from the soundboard moving and transmitting energy into the air. So, oddly, the soundhole isn't as important as some people think - it might contribute finishing touches to the sound quality but it isn't where the majority of sound comes from.

So, the problem is to work out which forms of vibration in the soundboard are important in producing the aspects of a guitar's sound that we term "good". In seems to be that certain modes are much more important than others. The trick then is how to arrange things so energy is transferred efficiently from the strings into those modes.

One aspect of that is to place the bridge at or near an "anti-node" of a desireable mode. An anti-node being a point where the board moves a lot - as oppose to a node, which is a part which doesn't move (this is what forms the lines in a Chladni diagram). Actually, what guitar designers usually do instead is try to adjust the modes of vibration so relevant anti-nodes occur near the bridge - this can be achieved through bracing design.

Now, we have a problem in that cigar boxes are different from guitar bodies - different in shape, diffferent in size. So the modes that are important for cigar boxes may be different from those that are important for regular guitars (and may be different from one box to the next). However, some important lessons still apply: Some modes are more important than others. Just because you can make a box resonate by putting a tuning fork at an anti-node position doesn't mean that's where you want the bridge. You need to select an anti-node for a mode that works well across the planned tonal range of the instrument.

My feeling is that, if you want to find the best bridge position using tuning fork testing, you probably need to use a series of different tuning forks which are carefully chosen to cover the range of the guitar.  The trick would be to find spots that respond well and relatively evenly at a range of frequencies. Just using a single tuning fork might badly mislead you - in theory you might end up with a guitar that has a very strong response at one frequency and is quite dead at other ferquencies.

To an extent there might be a similar problem with tap testing - just because a spot gives some sort of resonance when you tap it doesn't mean it's the right spot. I think there must be a very subtle art to genuinely using tap testing successfully - you would need to be able to hear tonal variation in response as well as simple volume differences. In practice I think luthiers tend to use tap testing to confirm or do minor adjustments to things they have already substantially determined by other means.

 

For those intersted in the scientific research, other names worth looking out for include:

Graham Caldersmith, an Australian luthier who started out as a science teacher and became an academic working on aerophysics before his interest in folk music diverted him onto research on musical instruments.

Neville Fletcher, of the Australian National University and University of New South Wales, and Thomas Rossing, of Northern Illinois University, who put together a major reference work titled "The Physics of Musical Instruments". Fletcher is an especially fascinating character who's worked in all kinds of fields that you wouldn't think could be connected.

 

Permalink Reply by Mark Bliss on July 20, 2011 at 4:18pm

Micheal S. You still breathing? LOL!

Alright, first off, backing up a tad, John, I think you have another real work of art in progress there, Very nice well thought out designs and workmanship. Although some of Oilyfools comparisons may be a tad of a stretch, I think the huge intended compliment is well deserved!

Mark, that is a good summary there, but as you pointed out, just the tip of the iceberg. Thank you for the links too. Its funny that just as I began reading it I was thinking about the research I had seen where fine sand was used to visualize nodes.I also cant seem to find it right now, but read a research piece on the violin family where electronic means were used to similarly study the vibrations of the ENTIRE instrument at a downright microscopic level. Very cool stuff.

I also want to thank you and agree with the soundhole comments. Even on instruments way off the scale closer to "idealized" than any CBG will ever be, I am of the opinion that soundhole configurations are way over emphasized when it comes to air movement. Many people are of the opinion that the guitar sound comes from the hole as if it were some kind of speaker. Or feel that a proper "f-hole" is simply a sound hole. Either may be far more important as an overall "dynamic" element of the instrument in my opinion. Here is a great example. Go to the home page and examine Shanes reproduction of his original Macanudo box guitar. Study the f-holes. Note the location relative to the bridge. Think about it. Now is there any wonder that he feels it had something special about its dynamic?

Also theres relative elements that never entered into the discussion, like that the neck and string termination is such a major factor in the overall sonority. Then theres the debate over headstock mass. (In short and over simplified, some feel minimum is best, while centurys of other opinion has added mass, both apparently feeling their approuch minimizes dampening of the strings vibrations.) The list goes on and on.

Now I am going to get this in before Micheal S. even gets a chance..........

The fact is that we are dealing with a great deal of limitation. Its a CBG, not a Strad. Or a Martin, and all that. OK, point taken and made. BUT......

I think the original question posted by John here is valid and I think this is a great discussion worth having (and worth reviving). I think the general question is this. How do we make the most of what we have (acoustically speaking)? Correct me if I am wrong John, maybe it was just to drive Micheal (and some of the rest of us) utterly mad!

Some of this old research and the related papers are literally from medieval studys by monks in monastarys!

Think about that!

Now heres my proposed theory. (Thank goodness its not likely to create charges of heresy and potentially lead to my being burned at the stake, as wild ideas might have in the time some of theses studies were done! Just maybe flamed in a forum. Cool!)

If you want to get maximum acoustic output from these small boxy designs, accepting that acoustic output wise, bigger is just about always better, so maybe we should think more along the lines of the violin. These little things are capable of such volume as to be literally hazardous to the players hearing over time! (Of course proximity is a factor too)

Think about the key points of the design. Very low mass top and bridge. Look at the way the f-holes free up the top to MOVE. Well tuned top and minimal/well designed bracing, idealized for the desired frequency range.. Take full advantage of the top for treble response and the back for some additional bass output. (Minimize muting of the back somehow, such as the "false back" designs some have tried.) Seek a sweet spot for string tension on the bridge. Make every effort to minimize any muting/absorbsion by any hardware or fittings. Etc.

One area I have not yet located and seek is some history and thinking on the bass bar/tone bar arrangement that is the centurys old standard. It is very interesting and so minimalist, yet works so well. I ponder why it hasnt been used, modified, adapted to other instrument designs.

I would be interested in any comments on this specifically from the deep thinkers and philosophers here. If the back were free to vibrate and utilized, why not try a bass bar and tone bar type arrangement in our context? Hmmmm?

As always, JMHO. And thanks for keeping it interesting folks!

And I'd like to extend a thank you to Shane, this site has entertained me beyond explanation for quite some time, and I am of the opinion it has "accidentally" expanded amatuer lutherie in a major and interesting way!

Permalink Reply by Ron "Oily" Sprague on July 20, 2011 at 7:44pm

Mark and Michael,

You have written explicitly in detail about things to which I was alluding ( because I had limited time and am typing on an IPad virtual keyboard). The reason I posted the links to tuning fork sets and mentioned the frequency behavior of a standard 6-string, is exactly that to truly implement John's tuning fork idea, you'd have to test the frequency response of the soundboard across the appropriate frequency range (precisely what the Chladni plate diagrams show!). If you wanted to truly get into this so deep that no one would ever want to speak to you again, you'd frequency test every aspect and part of the guitar, starting with the wood, and repeat at every stage of a build. I mentioned Charlie Kaman of Ovation fame before ( http://www.ovationguitars.com/whyovation/kamans_story ; http://128.102.4.175/factsheets/get_success_story.php?id=463 ), but I'm also aware that Bob Taylor of Taylor Guitars has taken his expertise to this level of testing detail, which is why Taylor turns out such routinely beautiful instruments.

Permalink Reply by Ron "Oily" Sprague on July 20, 2011 at 8:22pm

Now you've all done it! You made me go and find this site:

http://www.guitarengineer.com/index_files/Page578.htm

Finite element analysis of an acoustic guitar. Now, who wants to get a Ph.D in CBGs?

Permalink Reply by Roadkill a.k.a. John Maw on July 21, 2011 at 7:54am

First, I want to say that I am completely out of my depth in this company (the two Marks and Oilyfool), and I'm sure you didn't need me to tell you that. More for the benefit of others reading this I would like to make a couple of observations. A quick bit of background might be a good thing. I studied violin and then viola for 16 years (was at the Royal Academy of Music in London for the last five of them). Gave up to make bows for violin, viola and cello (fiddle sticks) for 11 years. Now a photographer for the last 15 or so. Also a bit of a low budget Hi-Fi nut (love the cheap valve amps). 

The first point is in relation to the sound hole debate and links to my observations with speakers. If I play a piece with ample bass on the Hi-Fi I feel a lot of air moving back and forward through the front facing ports on my speakers. With treble, much less so. Not surprising since the bass cone is bigger and can shift a lot more air. I had always assumed that the main role of the port was to allow the pressure inside the speaker housing to equalise with the outside pressure. If this didn't happen then the cones, and in particular the bass driver, would be damped to some extent (not sure how this explains un-ported speakers). 

Now back to cigar boxes. On some of mine I do quite a bit of finishing work to the box before I cut into it. Polishing oil gets into the join between the lid and the box and sometimes makes an imperfect seal. I find that once I cut for the neck the tap tone of the box changes and becomes lower. I assume that this is because the hole allows the air pressure to equalise faster and so removes any damping of the lower frequencies. 

Second brief observation is that there is an assumption on this site that a bigger box gives a louder instrument. That may be true, but a violin has a much smaller body than a cello but can compete comfortably. A viola has a bigger "box" than a violin, but it is a rare viola that can produce the same volume as a violin (hence many of the viola player jokes in orchestras). Is it nor more correct to thing that the body size should reflect the register in which the instrument plays? 

On the subject of comparing the violin family with guitars (cigar box or otherwise). My understanding is that the two are very different (not much of a surprise there). A new violin will take around a hundred years to "play in", whereby its tone improves through constant playing. It will eventually play out, but that is also a process of hundreds of years, which is why old instruments are valued so highly. As far as I am aware, an acoustic guitar will play in and play out in around three to four years in the hands of a full time working professional guitarist. The guitar has a much weaker structure than a violin, which accounts for the difference. 

OK. I'll trot off now and try to get to grips with playing these things.

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