Glass Bottle Resonator Dulcimer
General mountain dulcimer or music discussions
I applaud your creativity. I would never have thought of a concept like this. Keep up the good work.
That is interesting. Butch Ross mentioned the concept in our last meeting and I have it on my list of things to learn more about. My latest steel string design seemed to sound best with no soundhole and I have been wondering if the rounded back would still work. I guess I will have to try it with and without a soundhjoe and see how it turns out.
Your bracing is very similar to the Taylor V bracing. I have attached a photo of the bracing used on the dulcimer that Butch Ross is getting. I refer to it as parallel bracing. It is used with strings terminating at the bridge like a guitar. On my dulcimer it yields a rich tone with a strong bass response.
The next photo is of the dulcimer for Aaron O'Rourke. It is a modified X-braced pattern that has more attack and is less bass focused. I would say it is closer to a traditional dulcimer sound.
The remaining photos are of my newest design with strings that terminate at the end block. Very close to the prior X- braced design with one small addition. This is the loudest dulcimer I have produced (the one with the 0.100 soundboard).
Are you using a rounded bottom for more projection?
I am very intrigued by your solution to the problems of dulcimer design. The fact that you found a way to improve volume and still retain the tone you were after is particularly impressive. Are you using any bracing on the underside of the soundboard? As far as bowing of the fretboard goes, you have effectively isolated it from the forces and torque that would normally cause it to bend by limiting its contact with the body to a very small area. This is a significant improvement over most approaches.
My latest designs use a violin style bridge, but in some cases I found I needed to alter the bracing pattern in order to obtain an acceptable tone. In a few days I will be delivering new steel string designs to Aaron O'Rourke and Butch Ross, and another design to Aaron that may be usable for both steel and nylon strings. Interestingly, Aaron and Butch chose instruments with quite different tones when presented with prototypes, which supports the theory that there is no one perfect design. I am anxious to hear what each of them do with the dulcimers. Aaron and Butch are about as far apart on the technique spectrum as you can get so it will be an interesting comparison.
As magical as the dulcimer is, it is still bound by the laws of physics and basic engineering principals. The engineer in me is compelled to try to explain why all parts of a dulcimer between the string attachment points are under a bending moment, regardless of where the strings are attached. Let me first define a few terms so that we can communicate.
Neutral axis- all bodies (dulcimers included) have a neutral axis that runs the length to the body. When deflected, parts of the body on one side of the neutral axis go into tension while parts on the other side go into compression. If you have a board supported at each end and you load the middle with a weight, the top of the board will be in compression and the bottom in tension.
Force- a force has both magnitude and direction. For the string of a dulcimer, the force is defined by the tension in the string and the location of the string in space.
Moment- the moment (or torque) on a body is the force on the body times the distance from the neutral axis to the line of action of the force.
If we reduce the dulcimer to a simple block of wood, say 2” x 5” x 30” to examine the loading from the strings, we will be able to see why the block is under both a force and a moment from the string tension. Before we get to the actual loading case for the dulcimer, let’s examine the hypothetical case of the strings running right down the middle of the block of wood (1” from either edge and right on the neutral axis). The body of the dulcimer will be under pure compression loading. So if the string tension is 80 pounds and the cross sectional area of the block is 10 square inches, the stress on the block is 80/10 or 8 pounds per square inch. But the string doesn’t run through the middle of the dulcimer, it runs above the body. For this example, let’s say it is 0.25” above the block. The block is still seeing the same compressive loading as before, but now there is an additional moment added to block because the string is not running through the neutral axis. The moment is the tension (80 pounds) times the distance from the neutral axis (1.25”) or 100 inch pounds. This bending moment acts on all elements of the dulcimer body and is the enemy when trying to keep the dulcimer from taking a permanent deflection over time. Exactly how and where the strings attach has no impact on the fact that entire body of the dulcimer between the attach points is under this bending moment.
In an actual dulcimer, the analysis can be quite complex because of the large number of components, many of which have shapes that change as you move from the head to the foot, but the loading is there nonetheless. So as a designer, the challenge is to make sure the structure of the body is adequate to resist the inevitable bowing that will occur. The phenomenon of creep in wood is well documented and is generally thought to have no lower limit of loading for it to occur. If the loading is low enough, the creep may not be apparent over a few decades or even a few lifetimes, which is probably good enough for an instrument. Without dropping over the cliff of engineering analysis, we can try to reduce potential “weak spots” in our dulcimer body. A prime culprit in many designs is the strum hollow. You can greatly reduce the likelihood of a bowed dulcimer by reducing or eliminating it. Most players do not restrict themselves to just strumming over the hollow anyway.
It is this insidious creep that has prompted me to use carbon fiber in my instruments. It has many admirable properties including resistance to creep, extremely high strength to weight ratio and amazing stiffness. These properties come with serious health hazards that demand precautions that are expensive and time consuming to implement. Over time I would love to get to the point where I can eliminate it from my designs and be confident that they can survive for a century or two. The great part about lutherie is that there is always more to learn.
Matt, Thank you for posting your recent build. Not only does is show your excellent workmanship, it has some interesting design features. I am happy to see others getting the neck up off the soundboard. We might be starting a revolution. Could you further explain “single peg”? I also see that you are interested in bass dulcimers, which is great. There is a lot of opportunity for improvement in both baritone and bass dulcimers. The elevated neck will be a big benefit for the lower frequencies as I am sure you realize. I put bass strings on one of my new steel string designs recently and was pleasantly surprised at the result. It too had an elevated neck and modified X bracing. It sounded great when Aaron O’Rourke played it, but he could make a peach crate with a wire stretched over it sound great. I am building one for a client that will be ready soon.
I do not sand my soundboards to a set thickness. I attempt to sand them to a known stiffness, letting the thickness be the variable. Each soundboard is tested for deflection with 12” hanging over the bench and a known weight put on the end. I then sand until I reach an established deflection. It is surprising how much the thickness varies even within a species. I have seen thicknesses form 0.140 to just under 0.100 with one very stiff piece of Port Orford Cedar. This is a very large range when you consider that the stiffness varies with the cube of the thickness. Put another way, if you sand to a set thickness you will have widely ranging stiffnesses (and therefore volume and tone). If you are interested in this sort of thing, I highly recommend “Left Brain Lutherie” by David Hurd. It is a bit technical for some, but you don’t have to be an engineer to get some useful information. The book is written for guitar family instruments, but most of it is transferable to dulcimers.
If you are going to put a truss rod in I would definitely use an adjustable one- preferably double acting so you can correct in either direction.
I have to respectfully disagree with Ken on the point of the strings not putting a bending load on the neck and even the whole body of the dulcimer. The approximately 80 pounds of tension does put a bending load on the neck with most designs. It may transfer through other components, but ultimately the neck is loaded. I have repaired many dulcimers where the neck is permanently bowed over and eighth of an inch along its length (resulting in raised action that makes them unplayable). Some of these were built by respected builders whose names I will not mention. Wood under tension will creep over time. Carbon fiber and steel (a truss rod) will deflect under load, but do not creep.
Nate, I use carbon fiber stiffening in my necks for several reasons. I strive for very low action, which requires a neck that stays straight within a few thousandths of an inch. I also think that a stiff neck is good for making a responsive instrument. Any energy going into flexing the neck is not generating sound. Lastly, I have seen, and personally repaired, too many dulcimers with bowed necks that have made them unplayable. I would love to get away from using carbon fiber. It is expensive and there are real health hazards associated with machining it. Parts done on the cnc router have to be done under water to minimize the risk.
I have also seen many dulcimers that have survived many decades with no issues. Design and material selection are probably the keys to success.
Getting back to your original question, if the neck runs the full length of the instrument, a truss rod isn't a bad idea. They are relatively inexpensive (about $15) and work well to correct any bowing that might start to develop. The only down side I can see is that they do add some weight to the instrument.
You always have such great questions. I wish we had more answers that we know to be absolutely true. I have a few thoughts based on a recent dulcimer that I just completed. This is the loudest dulcimer I have ever built by a considerable margin. It contradicts almost everything I thought I knew about how to make a loud dulcimer. Since my instruments are non-conventional in design, these comments may not be of much value. The entire top of the dulcimer is free to vibrate independent of the fretboard since the fretboard is held above it on posts from below. The top is western red cedar and is thinner than is typical for my dulcimers, about 0.100 inch. It is braced from below with a modified X-braced pattern. The strings terminate at the end block. The bridge just sits on the top. So acoustically, it is very similar to an X-braced flat top mandolin. As an aside, mandolins prove that size is not the key factor in making a loud instrument. This dulcimer also has a double back, which I am pretty sure helps the volume- especially if you play with the dulcimer in your lap.
The big surprises were that this string configuration was louder than terminating the strings at the bridge- guitar style. One would have thought that the torque put on the top from the guitar type bridge would generate more volume than the slight downforce from the mandolin arrangement. Apparently not.
The second unexpected result was that blocking off the soundholes completely made no perceptible reduction in the volume. So there goes the large soundhole theory. Blocking did affect the tone, however.
I think you are on the right track to keep the vibrating mass as low as possible. I don't think the total weight of the dulcimer is all that important. The more soundboard you can get into play will likely help too. Fretboards that are in contact with the top for its entire length put severe limitations on volume and tone. I know that this is the way it has traditionally been done, but if you want to break away from result that is typically achieved, you will probably have to strike off in a new direction. I applaud your attempts to push the envelope. Please continue to push the rest of us and share your results.
This has been a very interesting discussion from the luthiers point of view. Many good thoughts. I have one additional thing to consider when purchasing or ordering a new dulcimer. Look for a fret height of around 0.047 plus or minus a few thousandths. This is higher than the typical dulcimer fret. With the higher fret you can "cheat" on your cord stretches. By this I mean that you don't have to have your finger right behind the fret to achieve a clean tone. In fact, you can be 1/2" or more behind the fret and get away with it. This can make a huge difference to your playing. Aaron O'Rourke turned me on to the use of high frets when I was building his first nylon string dulcimer and I instantly became a fan. Watch his videos closely and you will see that at times he takes full advantage of the high frets. I have since switched all of builds to high frets as standard.
I will also comment on the topic of VSL. I feel that with the appropriate instrument design, you can achieve virtually any tone you want out of a 25" scale. My nylon string dulcimers and my prototype steel string dulcimers have 25" scales. There is no need to fight with a long scale if you have small hands (or just want to play more comfortably). There are many other attributes for the luthier to work with to achieve a desired sound. With so many builders out there it is very likely that, with a little research, you can find the sound you want at a size that works for you. If you look at the early dulcimers (prior to the Kentucky instruments) many have what we would now consider to be short scales. So you are not breaking with the roots of the dulcimer to play an instrument that is more comfortable for you.
Here are a few photos of the shipping crate that I use for the dulcimers I build. It's basically a plywood crate inside a cardboard box. There are additional wood stiffeners at the corners and at two places along the length so that the crate is not easily crushed. Total shipping weight is about 20 pounds. Dulcimers have been shipped all over the US with out incident. This may be overkill for some instruments, but when the value of the dulcimer is well over $1000 and it has taken 4 months plus to build, I feel the it is justified.
I just happen upon this post and this is a crazy cool dulcimer. I applaud your efforts to advance the state of the art. Any thoughts about putting a lid on it so it can't spill? Keep up the good work.
I agree with Dan's suggestions. Sustain comes from a rigid structure and light vibrating components. In my Aaron O'Rourke Fingerstyle dulcimers I use a fairly thick top (up to 0.150) to limit the sustain so the sound doesn't get muddy with fast fingerstyle play. The sides and back are 0.080 thick so they do add the the texture of the sound. On soundboards, I measure the longitudinal and transverse stiffness of the plate and sand until I get the stiffness that I am looking for. The stiffness is a lot more important than the thickness. There is a lot of useful information in the online book "Left Brain Lutherie" if you are inclined to venture into the technical side of instrument making.