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Post by tark on Jun 17, 2009 0:45:37 GMT
Steverino you are absolutely right - apart from the body the cones are the other vital part of the equation. Taking the analogy with loudspeakers and cabinets into account (with caution - resonator guitar cones in bodies are not exactly the same as loudspeakers) to reproduce bass you can either use a very large driver with a relatively stiff suspension or, as in many small modern (inefficient) loudspeaker and cab designs, a small but long throw driver with a very flexible suspension. This second approach wont work with a resonator guitar because the suspension needs to resist the tension from the strings and in any case the strings vibration wont produce large excursions. As you say the other alternative is to try and decouple or offset the string tension in some way. I think this tends to make any design too complicated and perhaps inefficient. I think maybe the auxiliary bass radiator approach might help where you have a second passive cone (not driven by the strings) perhaps mounted on the back of the guitar. I seem to remember this requires a sealed body. One of the problems with any body / cone design to reproduce really low bass is likely to be that you will lose treble response.
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Post by melp on Jun 17, 2009 9:40:53 GMT
Hi Guy's,
Wow, here was I thinking that while complex resonators were not rocket science, but after reading your comments I start to realise they are!
Interesting discussion. Now for my question. You are modifying the bass response by blocking off some of the grille holes in your Baritone Tri-cone and the comment was that the grill area was too large even for a standard Tri-cone.
Anybody have any idea how to determine what the area of the sound holes should be, I guess for a given body volume?
If this is a bit off topic, sorry, but if you could point me at a resource to figure this out it would be good - I am making a cigarbox guitar at the moment and it would be good to know how to get this in the right ball park.
regards
Mel
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Post by tark on Jun 17, 2009 23:01:42 GMT
Hi Guy's, Wow, here was I thinking that while complex resonators were not rocket science, but after reading your comments I start to realise they are! Interesting discussion. Now for my question. You are modifying the bass response by blocking off some of the grille holes in your Baritone Tri-cone and the comment was that the grill area was too large even for a standard Tri-cone. Anybody have any idea how to determine what the area of the sound holes should be, I guess for a given body volume? If this is a bit off topic, sorry, but if you could point me at a resource to figure this out it would be good - I am making a cigarbox guitar at the moment and it would be good to know how to get this in the right ball park. regards Mel The Wikipedia page for Helmholtz resonance gives the basic Helmholtz equation (eventually). The length of the resonant port for a guitar is the active thickness of the top. From memory I think this is 1.6 times the measured thickness (the air flow acts as though the top is thicker than it actually is). Now the complicated bit and what makes guitars different to loudspeakers. A loudspeaker cabinet should be designed to be rigid, massive and the walls acoustically dead. Guitar bodies are not - they vibrate and flex. The body vibration affects the resonant Helmholtz frequency and drives it down below what the basic calculation predicts it should be. Because of the differences in body stiffness wood and metal bodies react differently and I suspect the extra depth of the f holes in wood and in the rolled f holes in metal change the Helmholtz frequency and give those guitars a slightly tighter sharper resonance (higher Q). It is also difficult to know what the ideal Helmholtz resonance for a guitar should be - if the intention is to damp the principle bass resonance of the soundboard or in this case cone then the Helmholtz resonant frequency should be the same as the cone or soundboard resonance. However the Helmholtz resonance of a guitar body is normally fairly low Q. That is it is not a sharp narrow resonance but broad and flat so it interacts with the vibration from the strings in a fairly gentle way. My experiments suggest that the best sounding bass EQ is not necessarily with the Helmholtz resonance tuned to the main cone resonance. The best reference I know of for this stuff is - Left Brain Lutherie by David C Hurd. The other approach is to cut a fairly large sound hole and fit a temporary adjustable shutter or even cut a series of small sound holes you can fill in one by one. You can experiment to get the best sound and then fill in the holes you don't need in some fashion that looks like an intentional part of the design. If you cut wine cork sized holes you can use corks to block the holes as you experiment. A number of modern guitar builders have built guitars with all sorts of adjustable ports as permanent part of the design. I am a bit suspicious of this because normally there seems to be one ideal port size for tone (for any particular guitar). I guess I can see the utility of the electric Jazz guitar designs that allow blocking the ports completely because this can help stop feedback problems. I find it interesting that no one mentions that the round rubber feed back busters designed to block the sound hole in acoustic flat tops completely screw up the acoustic bass response but I guess the PA EQ is normally adjusted to compensate.
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Post by Michael Messer on Jun 17, 2009 23:26:23 GMT
This discussion is very interesting and a couple of the points made by Steverino about cones did get me thinking. However, I am not an engineer and would not stand a chance in a conversation about Helmholtz resonance and piston radiators. I am sure you guys know your stuff.
What I will say is that I have heard many round-neck Tricones during the past 35 years of being around this stuff, and when a round-neck Tricone sounds right, they are among the most wonderful sounding guitars in the world. The problem is that very few people have heard these instruments as not many round-neck Tricones do sound really great. Most are average. But when all the components are properly matched and the instrument has a certain 'rightness' about it, they sound amazing and they lack nothing. The best of them are as I said, about as good as it can get.
Shine On Michael.
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Post by Deleted on Jun 18, 2009 2:36:22 GMT
What I will say is that I have heard many round-neck Tricones during the past 35 years of being around this stuff, and when a round-neck Tricone sounds right, they are among the most wonderful sounding guitars in the world. The problem is that very few people have heard these instruments as not many round-neck Tricones do sound really great. Most are average. But when all the components are properly matched and the instrument has a certain 'rightness' about it, they sound amazing and they lack nothing. The best of them are as I said, about as good as it can get. so are round necks less consistent than square necks of the same design? If so, why? Or is it more the case that being originally designed as square necks tricones just never made the transition properly, i.e. there is a fundamental flaw in the design when applied to round necks. If this is the case does it hold equally for new ones such as those by NRP or Busker.
LR
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Post by steverino on Jun 18, 2009 7:20:59 GMT
I sure enjoy these meetings of the Armchair Engineering Society. I apologize if I have dragged things off topic, or into outer space even. It is just that in the world of loudspeakers I have seen so many examples of technological avenues going unexplored, or of really valid engineering concepts being underutilized then abandoned. In the world of resophonic instruments we have three basic designs, all springing forth from one brilliant fellow, John Dopyera. It strikes me that this realm could be, perhaps should be, broader by now. If any of this "wild hair" design talk leads to something useful then it will have been worthwhile, methinks.
The basic advantage of a resonator instrument, as I see it, is the relatively high mobility of the cone(s) surface. In brief, the aluminum can move further and more easily than the surfaces of a braced wooden guitar in response to string vibrations, and so produces a louder sound. I have heard resonator instruments described by my (admittedly warped) loudspeaker enthusiast friends as "louder output, narrower bandwidth" than wooden guitars. This may be the case, but strikes me that it needn't be so. The spider instrument I modified with a Schireson type bridge retains the loudness of a resonator, but its sound is more in the direction of a wooden guitar, and very pleasing.
In loudspeakers I'm a horn guy, so I haven't studied bass reflex theory too much. As I understand it, in classic BR theory, the box (Helmholtz) resonance is tuned to approximately the same frequency as the resonance of the cone in the box. That way the box resonance, which is 180 degrees out of phase with the cone, damps what would otherwise be a large response peak at cone resonance. With this technique the overall system response is usefully flattened and extended on the bottom.
One problem (or at least characteristic) of resonator instruments, it seems to me, is that the fundamental cone resonance is too high to usefully interact with the box resonance in the manner described above. In the (few) measurements I have made, the majority of the energy from the cone seems to be in the region of 200 to 600 Hz. Most of my work has been with spider bridge instruments, which I think have a higher cone resonance than most biscuit resonators. Even with biscuits, I would expect the cone resonance to be above 200Hz. when loaded by the strings. So, the frequency extension and flattening offered by the reflex loading goes largely unused, or at least it seems so to me. This situation is probably even worse with most wooden guitars, and there are many marvelous sounding instruments of both types, so perhaps this bass reflex analogy is flawed to begin with.
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Post by Michael Messer on Jun 18, 2009 9:57:27 GMT
Hello LR,
I knew that would get someone thinking about what I had actually said!
First of all - nobody makes a real metal-bodied square-neck Tricone anymore. I am talking about original sq-nk Tricones with hollow metal necks. So there is no comparison in the world of new Tricones.
In old 1920s and 30s National Tricones, as a generalization, square-neck Tricones are more consistently good instruments that round-neck Tricones. That is because they were designed as square-neck guitars and the design was adapted to become a round-neck. In my opinion and the opinion of many collectors; most round-neck Tricones are average, some not great at all. But when a good round-neck Tricone turns up, they are unbelievably good. They surpass everything that a great square-neck Tricone can offer. You have to understand that I am talking about just a very few guitars here. For example; Bob Brozman's Style 1 round-neck Tricone that he used to tour and record with. This is a monster Tricone with an amazing sound. Mike Cooper's Style 1 round-neck Tricone before he changed the cones, which he had to do because they had really gone. Mike's Tricone was partly responsible for a whole generation of British baby-boomers to start playing National guitars. The Harry Watson Style 4 round-neck Tricone - was owned by me and is now in the Notecannons collection. The 'Harry' is possibly the best sounding Tricone in existence. It has properties that I have never heard in any other National Tricone. Everything about it is perfect, which means that everything is matched perfectly....the choice of which three cones should go in the guitar, the neck wood, the body thickness....everything. This was a presentation guitar given the Harry Watson when he retired from National in 1931. Harry was the quality controller, so they weren't going to give him a bad one were they!!!!
I think there are many good modern Tricones, but apart from one brand, none of them (in my opinion) can compare to these great originals. Mike Lewis (Fine Resophonic Guitars) in Paris, is John Dopyera's spiritual protege. I don't believe that anyone in the world today has the understanding of Dopyera's original design that Mike Lewis does. His Tricones consistently come up as among the best Tricones I have ever seen. He builds both wood-bodied round and square-neck Tricones and metal-bodied round-neck Tricones. Here are three examples; Pascal Mesnier's Fine Resophonic Style 1 round-neck Tricone. This is an amazing guitar that is as good as anything I have ever seen. Louisiana Red and Eric Clapton's wood-bodied round-neck Tricones. My own square-neck wood-bodied Tricone.
John E Dopyera, the son of the inventor, when he met Mike Lewis and saw his work said that his father should have had Mike as his son!
A great Tricone lacks nothing; it has volume, full bass, clear clean sweet treble, warm rich mids, and an overall sweetness that is like nothing else.
I think National Resophonic Guitars produce consistently very good Tricones. Far more consistent than National ever did, but I am not sure if they have ever produced anything to match the guitars I have mentioned above. In some areas of construction they have improved on what Dopyera designed; they are less prone to buzzes and rattles, they play in tune up the neck and they are louder. They are now suitable for all types of players and sound great as blues guitars. But I am not sure if these improvements have taken the Tricone away from its original sweet warm sound that John Dopyera once desribed as...'the sound of a Tricone flows like a river'. This is a bit of a double-edged sword, because NRP's Tricones are definitely more consistent in their sound quality than original National Tricones were. But in making that consistency, which they had to do, somewhere along the line the instrument has become something else. Just listen to Jim & Bob and Sol Hoopii's recordings to understand my comments.
I am very interested in Steverino's last post, but cannot type any more for a while!
Shine On Michael.
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Post by tark on Jun 18, 2009 12:57:52 GMT
Michael you make some very good points. Comparison is everything and your experience of some truly great instruments is invaluable. It's something most of the rest of us don't have. What is so frustrating is that we don't know exactly what it is that makes these instruments so great. Perhaps Mike Lewis does know and he's keeping quiet! I have certainly noticed that side by side comparisons really show which instruments are good and which aren't. It is amazing that for a metal design where the variability of wood is, you might think, removed, that metal resonator guitars even of supposedly the same design, vary so much. I remember a post somewhere by Marc Schonburgh (sorry can never remember / get his name right) where he said he found that the order in which the three parts of a reso body were soldered together made a huge difference to the resonance of the metal parts themselves. I think he said the top should be soldered last to get it under some tension. And then of course there are the two piece bodies which are rarely, if ever, made these days. Steverino your comments that the bass reflex speaker analogy perhaps doesn't apply make some sense and I think you are right to some degree. I don't think it can be argued that the body / sound hole combination does NOT form a Helmholtz resonator because it very obviously does. As you say, what is uncertain is the resonant frequency of the loaded cone. Consider that for open G tuning the bottom string fundamental is around 73Hz and I think some of that must be reproduced at a reasonable level. For conventional acoustic guitars the Helmholtz body resonance is usually around 100Hz. As i said in my previous post in real guitars the Helmholtz resonance seems to act more as a general bass EQ rather than a direct attempt to flatten the main resonance of the top or cone. BTW here's a handy link to info on guitars and Helmholtz www.phys.unsw.edu.au/jw/Helmholtz.html
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Post by 1928triolian on Jun 18, 2009 13:25:45 GMT
I remember a post somewhere by Marc Schonburgh (sorry can never remember / get his name right) where he said he found that the order in which the three parts of a reso body were soldered together made a huge difference to the resonance of the metal parts themselves. I think he said the top should be soldered last to get it under some tension. And then of course there are the two piece bodies which are rarely, if ever, made these days. Hi Tark, if I can remember correctly, Marc Schoenberger said exactly the contrary: the best thing would be to have top and sides as one piece, and lastly back soldered on. This is the way National made (after the 3pc body period) their 12 frets guitars. However, here's the topic you were referring to.: www.guitarseminars.com/ubb/Forum1/HTML/018582.htmlhope this helps 1928
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Post by tark on Jun 18, 2009 13:48:18 GMT
Brilliant 1928T - thanks for finding that - so its tops soldered first for lowest tension is the best way.
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Post by bod on Jun 18, 2009 14:11:06 GMT
Fantastic thread this! Nice link to the site about music acoustics, too, like the way it gives a non-mathematical explanation and gives me more reasons for wishing I was better with numbers. Good questions LR.... I have a few more down the same path (Michael, if this is getting too far from the original post, just say and I'll ask my questions in a new thread instead)
So, insofar as I understand it - and I'm out of my depth again here, but keen to learn something if I can - the original tricones had square metal necks and these necks were of hollow construction - is it helpful or misleading to think of them as sort of more like a Weissenborn in this respect?
Not sure now, but I think I read somewhere that these hollow metal tricone necks were (sometimes? / always?) "filled" with a (drilled / chambered?) wooden insert, is that right? If so, was this more of a structural or acoustic thing (or both)?
So, I'm wondering: is the neck hollow on one of these continuous with the body chamber? (and would that matter?) Does the elimination of this design feature in some way amount to the amputation of a significant acoustic device? Why does no-one make such a design any more? (Madly intensive on the labour? Not enough demand?)
Also, is the neck on a Fine Resophonic wooden-bodied square neck tricone hollow (or does it just look like it might be)? (I sometimes visit the FR site just to stare in wonder at these, they do look just amazing, but for some reason the relevant page is in French and my French is barely better than my maths!)
Cheers
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Post by Michael Messer on Jun 18, 2009 14:27:12 GMT
Hi Bod, Some quick answers.... Original Tricones were definitely influenced by Weissenborn Hawaiian guitars. The hollow neck does act as an acoustic chamber. The wood is probably more of a structural thing than anything else, it stops the guitar from folding up when you put strings on it! But everything in a guitar adds to the sound and tone. Nobody makes metal square-neck Tricones anymore because the tooling would be very expensive and the demand would be very low. Most square-neck resonator players in the world use Dobro style guitars. The neck on a Fine Resophonic wood-bodied square-neck Tricone is hollow and constructed about as close to an original as possible, but with wood. My Fine Resophonic maple square-neck Tricone is a superb guitar. It is different to an original, but it has everything one could want from a Tricone. I have played it most days for the past eight years. Shine On Michael.
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Post by bod on Jun 18, 2009 16:00:33 GMT
Thanks Michael - just one more quick question for now, if I may: is that (very) Fine Resophonic squareneck tricone of yours conspicuously present on any of your recordings?
Cheers
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Post by tark on Jun 18, 2009 16:05:11 GMT
This is a very relevant point which I should have thought of before. The original Tri-cone design was drawn up as far as I know for the lap style hollow neck. The hollow neck guitars have a larger internal air volume because of the hollow neck and therefore proportionally the basket grille holes were more in keeping with the overall design.
When they started making the round necks they did not change the size of the basket grilles while the internal air volume got smaller. This is similar to what happens with wooden guitar designs that are available without and with cut aways, very often the sound hole remains the same size when it should probably be smaller on the cut away model.
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Post by Michael Messer on Jun 18, 2009 17:34:07 GMT
Hi Bod,
Yes, the maple Tricone is featured on Second Mind (Painting The Blues & Riverboat). I have recorded with it on many occasions, but those are the only two tracks on my CDs. Oh yes....it is on the Sound Techniques 'Guitar Maestros' DVD, check my website for details.
Shine On Michael.
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