An Interesting Dulcimer Experiment

Just share stories or offer advice

Postby Lurch » Tue Dec 23, 2008 10:21 am

I have really enjoyed following this thread, and look forward to more discussion. Thanks to all that have contributes here.
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Postby Howard Rugg » Sat Jan 03, 2009 6:52 pm

my brain hurts

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Postby Kathy » Sat Jan 03, 2009 9:01 pm

Howard Rugg wrote:my brain hurts

Howard


Ha Ha, :lol: That happens alot around here. :P

Kathy :)
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Postby Dulcimer Jim » Sat Jan 03, 2009 10:04 pm

.
Last edited by Dulcimer Jim on Wed Jun 10, 2015 2:10 am, edited 1 time in total.
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Postby TJisanass » Sat Jan 03, 2009 10:43 pm

Isn't there some sort of instrument, which can be attached to the wood itself, capable of measuring vibration in the wood?
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Postby mrchips » Sun Jan 04, 2009 12:02 am

This thread is downright intersting. I might try my hand at a MD from scratch sometime this winter. :lol: :lol: When a tune isnt taling Ill often start a pickin stick thingy. :lol: :lol: From threads like this just about anyone with a couple years of butchering wood can make anything. :lol: :lol: :lol:
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Postby PaulC » Sun Jan 04, 2009 10:19 am

mrchips wrote:This thread is downright intersting. I might try my hand at a MD from scratch sometime this winter. :lol: :lol: When a tune isnt taling Ill often start a pickin stick thingy. :lol: :lol: From threads like this just about anyone with a couple years of butchering wood can make anything. :lol: :lol: :lol:


Or at least rationalize the results... 8) :lol:
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Postby rtroughear » Mon Jan 05, 2009 10:36 am

DJ : The paper top dulcimer is like the Yocky in your picture in that it has a bridged fretboard (but with four arches instead of eight). I think the commonly promoted argument of "freeing up soundboard area so it can vibrate more" is a spurious one. It's a natural cross-over from how a guitar top behaves, but I can't find any evidence that mountain dulcimers act that way. Who's to say that more vibration is necessarily better vibration, in any case. And what parts of a dulcimer vibrate anyway, certainly not only the top? Also, mass is a consideration, but not the only one. The stiffness of the fretboard is a defining factor in how it will vibrate, and a typical fretboard has a stiffness that dominates the top plate to the extent that the top plate mass and stiffness is almost irrelevant. The top will vibrate as the stiffness of the fretboard/box combination dictates - not in its own right. I don't think of the fretboard as a brace ie. something that modulates the tone or adds strength, or both. It's more of a major structural component. Depending on how a fretboard is shaped, and the material it is made of, a hollow fretboard and an arched one may have the same weight and stiffness, and then maybe produce similar sounds. (Daryl "Thud" raised this in another recent post).

Some of this is semi-speculation, and I'm getting ahead of what I actually know, which will have to wait until I've done some experimental studies (which is just as likely to confuse things further). But I'm moderately confident that the main role of the top is to contain the air in the box, and it doesn't matter very much what it is made of. I also do think that the fretboard is an important contributer to the sound (but not because it is arched or hollow, or solid for that matter), and is worthy of further investigation to see what it's affects are.

All this relates to full length fretboards. There will come a point, such as 1/2" top-plates, and 1/4" fretboards, where things start to get reversed and tops become more important than fretboards in setting stiffness - but those won't be on a typical mountain dulcimer.

Wabi-Sabi: Cheap piezo pick-ups do a pretty good job - picking up wood vibration is what they are designed for.

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Postby mrchips » Mon Jan 05, 2009 12:02 pm

One cannot take what makes a necked really good and transpose that to a neckless one and get the same results. While you can find a number of real in deph what makes it work on nearly any necked insterment just try and find the same for a MD or a HD for that matter. :lol: :lol: A lot will transpose but a lot wont. One thing that happens with a MD fretboard that is tottaly different than say an insterment where the fretboard is on a neck is this.

On a MD the stifness of the fretboard acts a lot like having a brace under the top ful leingth on a necked insterment. At the very least the result is it seperates the MD top into nearly 2 independant resonating areas.. As one function of what is esencally a nearly closed box with a hole in it is that it will resonate at some givin note.. An unbraced top will act as one complete viberating surface. A top that is stiffened by a brace in any form will have mutiple viberating areas.

A typical gutar top does have braces under it but as litle as possible but still enough to keep it from colapsong due to inward force of the bridge. As there isnt any traditional bridge to deal with on a traditional MD no braces are needed. But at the same time the fetboard does act like one.

The volume of the sound box and the size of the soundholes on both do change the sound.. Size the relationship between the hole and soundbox volume just right and you can quiten down some note that would otherwise be ringing or to boost a quiet note.

While necked insterments an the traditional MD are two tottaly different insterments theyre more alike than many realise as far as the physics of sound goes.. Even the shape of the soundbox affects the sound. All else equal, including hole size a bigger bow will have more low end than a smaller one for example. Anything you do to an insterment will affect the sound to some degree and what makes a good insterment good as far as tonal quality goes is to find the right combination of shape, size, wood etc..

The perfect balance as far as a maker goes is usally arrived at by trial and error over many insterments made. There is a whole bunch of mathmetal models that do get quite close to what an insterment wil sound like but unless you enjoy math at a level that very few understand, they still dont predict the sound completely. Close but not exactly. Thats not to say the non-perfect ones are bad, its just as they dont sound perfect to who makes it. By using that hard earned knowlede a maker can make one with tonal qualitys according to what the person requests.

This little thread has given me a number of insights into how a MD really works. :lol:
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Postby JimP » Wed Jan 07, 2009 12:56 pm

This thread raises the question for me as to why not use spruce for the back if that is the soundboard?
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Postby Ken Bloom » Wed Jan 07, 2009 1:14 pm

Jim,

You have hit a very good point. On concert zithers the back is always spruce, usually veneered. The cheaper ones leave off the veneer. Many of the European zithers and dulcimer-like instruments have hardwood tops and spruce backs.

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Postby PaulC » Wed Jan 07, 2009 1:47 pm

...And what parts of a dulcimer vibrate anyway, certainly not only the top?...


The bottom clearly does - the sitting on the lap vs. possum board effect illustrates this quite well. It wouldn't be difficult to fix a test dulcimer by it ends and selectively dampen portions of it for observed effect. The vibrations originate from the struck strings of the fretboard. An attached top is going to exhibit one of three effects - alter the sound by moving a larger volume of contained air (with an attendant frequency shift), diminish the sound by reducing the transmission of vibrations (or selected frequencies of vibrations) or no net effect. Your experiments suggest that all three occur but subjectively the third alternative seems to be dominant. It could be that the effects noted are not top dependent, but on something else.

I suspect the above experiment will show the nature of the bottom and the contained volume will have substantially more effect than the top. The bottom reflects as well as sustains, hence the observed quality of sound derived from material choice. Different densities will attenuate different frequencies.

It could also be that a top, depending on material and distance from bottom, could diminish some frequencies by wave cancellation. Standing waves of some tones may cancel in the contained geometry of an enclosed dulcimer, something that can't happen (to the same degree) with a topless or acoustically transparent instrument.

This is I believe, the explanation behind lightweight "tone" tops such as spruce tops. My view is that they are among the most acoustically transparent of the wood species used for instrument manufacture (due to their large empty cell structure and relatively low mass), with the result that the vibration of the contained air and reflection from the bottom is able to reach the ears with less interference (ie, passes through the "tone" top unhindered e.g. spruce), giving the sense of a better performing instrument. Sound will project away from the denser material. Therefore instruments with an acoustically transparent (more so) panel and a denser reflective panel, will out-perform instruments where both panels are the same (either dense or transparent, all other things being equal). So-called tonewood tops on guitars allow the projection of sound forward, rather than back, thus giving the sense of a more resonant "better-sounding" guitar. The open-back vs the resonator banjo bears this out in practice, and the reason for the resonator in the first place.
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