Jack Devereux

Basic Acoustics Resource

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I feel like I'm beginning to have enough grasp of tool skills to kinda make a decent, repeatable box to a set of specs, and am now trying to be more systematic about documenting both the things I can control (arching, graduations, bar shape, whatever else), and the qualities of the wood I'm using. 

I hear all these terms and concepts about wood density, modes, speed of sound, all that jazz thrown around that I don't really understand, and would like to learn about this stuff, if only for note taking purposes. Is there a website, book or something else that breaks these basic violin making acoustics concepts down? I've searched and can't seem to find anything that seems definitive. 

Thanks!

 

 

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Fundamentals of Musical Acoustics by Arthur Benade is a book that Norman Pickering recommended to me, when I was first getting into this.

http://store.doverpublications.com/048626484x.html

or https://www.amazon.com/Fundamentals-Musical-Acoustics-Second-Revised/dp/048626484X

I'd be happy to lend my rather dog-eared copy to anyone local.

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I have the Benade book also. 

It takes a very interesting path through the topic. I found it helped develop my intuition for more complicated real situations. Certainly goes beyond most standard presentations.

 

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Awesome, thanks! 

 

 http://www.fiolinmaker.no/en/tips_tricks/eigenvekt.php 

 

I just used this site to calculate the density of a back I had laying around and came up with 2.123g/cm^3. What does this tell you? When you're thinking about wood densities do you just record and find what trends tend to work for your style of making, or do you actually seek out wood in a specific range? Are there characteristics that woods of different density typically display? 

 

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19 minutes ago, Jack Devereux said:

Awesome, thanks! 

 

 http://www.fiolinmaker.no/en/tips_tricks/eigenvekt.php 

 

I just used this site to calculate the density of a back I had laying around and came up with 2.123g/cm^3. What does this tell you? When you're thinking about wood densities do you just record and find what trends tend to work for your style of making, or do you actually seek out wood in a specific range? Are there characteristics that woods of different density typically display? 

 

Are you sure about the density you measured?

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56 minutes ago, Jack Devereux said:

I just used this site to calculate the density of a back I had laying around and came up with 2.123g/cm^3. What does this tell you?

36 minutes ago, Greg F. said:

Are you sure about the density you measured?

21 minutes ago, Jack Devereux said:

No, I have no idea what the range even is. Is that wildly off? There's a solid chance I entered the measurements wrong...

If you don't come out with a number between .5 and .8 g/cm^3 for maple, you did something wrong.  Or it's not wood, but some kind of metal.

 

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3 hours ago, Jack Devereux said:

Awesome, thanks! 

 

 http://www.fiolinmaker.no/en/tips_tricks/eigenvekt.php 

 

I just used this site to calculate the density of a back I had laying around and came up with 2.123g/cm^3. What does this tell you?

 

It tells me either that the calculations you used are way off, or that you have found a wood way outside the range of any maple I have ever run across.

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Hahaha, yeah, I suspect I just entered the dimensions into the box wrong. I'll try it again and report back...

 

Are there general correlations between density and sound or is that over simplistic? 

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I believe there is a correlation between density and sound preference of listeners---zero.

I do however believe that there is a reasonably strong correlation between the top plate weight and listener preference.

If you put the above two comments together you could come to the conclusion that plates of low density wood should be thick and that plates of high density wood should be thin.

Or in other words everything can be made to work.

Or don't worry be happy.

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9 hours ago, Marty Kasprzyk said:

I believe there is a correlation between density and sound preference of listeners---zero.

I do however believe that there is a reasonably strong correlation between the top plate weight and listener preference.

If you put the above two comments together you could come to the conclusion that plates of low density wood should be thick and that plates of high density wood should be thin.

Or in other words everything can be made to work.

Or don't worry be happy.

I was taught to consider density when choosing arching height. A low density piece needs the support of a higher arch, and ultimately it will be easier to get to your target weight and flex with normal graduations. Conversely, a more dense piece should get a lower arching, which will also make it easier to get to your target weight and flex without going thinner with the graduations.

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48 minutes ago, TimDasler said:

I was taught to consider density when choosing arching height. A low density piece needs the support of a higher arch, and ultimately it will be easier to get to your target weight and flex with normal graduations. Conversely, a more dense piece should get a lower arching, which will also make it easier to get to your target weight and flex without going thinner with the graduations.

 

Although it may seem logical,  I'm not entirely convinced of this theory.

If we take the case of two archings of equal height and equal thickness, the one with denser wood will be heavier.

So to reduce weight and increase efficiency it may be necessary to raise the arching with thicker wood to be able to decrease the thickness and so the weight.

Instead, raising the arching with the low density wood would probably result in an excessively high tap tones frequency i.e. an excessive stiffness.

In my empirical working experience this works, but maybe somebody with clearer ideas about physics might disprove.....

 

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1 hour ago, Davide Sora said:
 

In my empirical working experience this works, but maybe somebody with clearer ideas about physics might disprove.....

Sam Z. also has mentioned using higher arching with denser wood in order to keep the plate weight down and stiffness up.  If taptone and plate weight are used as targets, then physics supports this method.  However, physics has no way to tell whether this maps into a better or worse sounding instrument at the end, but does hint that different archings with different wood are likely to behave somewhat differently, regardless of matching plate taptones or body signature modes.

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7 minutes ago, Don Noon said:

Sam Z. also has mentioned using higher arching with denser wood in order to keep the plate weight down and stiffness up.  If taptone and plate weight are used as targets, then physics supports this method.  However, physics has no way to tell whether this maps into a better or worse sounding instrument at the end, but does hint that different archings with different wood are likely to behave somewhat differently, regardless of matching plate taptones or body signature modes.

Nice to know I'm in good company.:)

However, I fully agree with your last sentence and that is why absolutist theories can never convince me completely.

My main concern is to deal with what works best for my overall construction strategies and acoustic results, without worrying too much about finding some theory that may explain them.....;)
 

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1 hour ago, Davide Sora said:

My main concern is to deal with what works best for my overall construction strategies and acoustic results, without worrying too much about finding some theory that may explain them.....;)

From what I have observed, that method is by far the most effective at producing positive results.  

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 We like to adjust things (plate thickness, arch heights etc.) to compensate for the scatter in wood properties in order to get the same sound character.

But here is also a lot of scatter in what players like.  I'm starting to get confused.

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3 hours ago, Don Noon said:

Sam Z. also has mentioned using higher arching with denser wood in order to keep the plate weight down and stiffness up.  If taptone and plate weight are used as targets, then physics supports this method.  However, physics has no way to tell whether this maps into a better or worse sounding instrument at the end, but does hint that different archings with different wood are likely to behave somewhat differently, regardless of matching plate taptones or body signature modes.

Is ideal wood defined as a density that lets you use an ideal thickness and arch?

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53 minutes ago, Bill Merkel said:

Is ideal wood defined as a density that lets you use an ideal thickness and arch?

I don't believe in ideal anything (wood, arch, thickness, appearance) when it comes to violins... except as defined by what someone will like and buy, which is highly  variable.

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Given the five variables, density, arch height, thickness, plate weight, and stiffness, how would you (anyone) rank their effect size on the outcome on achieving your acoustical target?  I realize there's some inter-dependencies among these variables.  I would think arching and stiffness would be in the one and two slots, and density may dictate the bounds in which these can be achieved within "normal" parameters.  The last statement forces density into some form of acceptable range.  Plate weight, density and thickness are not independent, so that muddies the water.  A better question might be in what order during a build do factors come into consideration?  I would rank density as first to decide arch height.  Then thickness to achieve a target (range?) of stiffness, with plate weight and thickness as being parameters to stay within while trying to achieve some stiffness.  Am I in the ball park here?  

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12 minutes ago, Jim Bress said:

Given the five variables, density, arch height, thickness, plate weight, and stiffness, how would you (anyone) rank their effect size on the outcome on achieving your acoustical target?  I realize there's some inter-dependencies among these variables.  I would think arching and stiffness would be in the one and two slots, and density may dictate the bounds in which these can be achieved within "normal" parameters.  The last statement forces density into some form of acceptable range.  Plate weight, density and thickness are not independent, so that muddies the water.  A better question might be in what order during a build do factors come into consideration?  I would rank density as first to decide arch height.  Then thickness to achieve a target (range?) of stiffness, with plate weight and thickness as being parameters to stay within while trying to achieve some stiffness.  Am I in the ball park here?  

Smart thinking!

I fix two of those parameters; weight & stiffness

Arch height is determined by the woods performance and thickness by density

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54 minutes ago, Don Noon said:

I don't believe in ideal anything (wood, arch, thickness, appearance) when it comes to violins... except as defined by what someone will like and buy, which is highly  variable.

On the other hand without some ideal, random would be fine.  I remember you quoting Z. something like it takes the best wood to make the best fiddle.  I was wondering what part the best wood would play; maybe allow ideal arch and thickness.

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7 hours ago, Davide Sora said:
 

 

Instead, raising the arching with the low density wood would probably result in an excessively high tap tones frequency i.e. an excessive stiffness.

 

 

I would say in this example the higher frequency is not the result of excess stiffness but less mass.

Performance wise, IMO, this is a fault of ultra light materials. 

If we have two bars of identical dimension the one with the higher frequency is not necessarily stiffer. We can say it is stiffer only if the two bars are also the same weight.

If they are the same frequency the heavier one is stiffer.

density and stiffness should not be lumped together interchangeably.

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3 hours ago, Bill Merkel said:

On the other hand without some ideal, random would be fine.  I remember you quoting Z. something like it takes the best wood to make the best fiddle.

What he actually said was that almost any wood can be used to make a good violin.  When asked about the ultimate in power and projection (not necessarily good for everybody), then he said you need very good wood.

I don't go along with random being the result of not having an ideal, similar to not believing in an ideal voice or the perfect piece of music.  Many things can be good in different ways.  Similarly there are infinite ways to be bad.  Although in the end it's all subjective, I think it is possible to find general (but not perfect) agreement about some things.

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