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Measuring the Velocity of Sound in wood - directly


catnip

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If I use RR = c/rho

Name------- rho------- c------ c/rho

lead ------- 11.35 -----1322 ------ 116

aluminum ----2.7 -----4877 ----- 1806

maple --------0.62 ----4110 ------6629

If RR is related to low damping (higher RR means lower damping), then maple would have less damping than aluminum. Seems wrong to me.

I Googled "radiation ratio" and found no hits. It must have a synonym.

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I Googled "radiation ratio" and found no hits. It must have a synonym.

I got a lot of hits when I did it, but I'm not sure that the radiation ratio being discussed here is the same as the radiation ratio discussed elsewhere. The quick search that I did turned up this book entry, http://books.google.com/books?id=jDeRCSqte...ion&f=false

I also found a scientific article using the radiation ratio as well as a finite element model to study sound radiation from train wheels. It looks very interesting but I don't have time to dig into it. They seem to have used a radiation ratio like the one in the book.

These two sources are using a radiation ratio that requires knowing the mode shapes (or at least average values derived from the mode shapes) involved in the vibration. Is that being taken into account with the radiation ratio discussed here or is this a different radiation ratio?

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Curtin used the term "radiation ratio" in his tap tone article. To be comparable with his numbers, everything needs to be in units of meters, kilograms, and seconds.

Radiation ratio has absolutely nothing to do with damping. It is essentially a measure of stiffness and density only.

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Curtin used the term "radiation ratio" in his tap tone article. To be comparable with his numbers, everything needs to be in units of meters, kilograms, and seconds.

Radiation ratio has absolutely nothing to do with damping. It is essentially a measure of stiffness and density only.

It appears radiation ratio is simply an empirical term derived from measurements only, i.e., it's just a lab-generated "number" used in an effort to characterize sound output. That's not to say radiation ratio may not be "useful", but, it is what it is [only].

Jim

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What sorts of distances are we talking bout. Say for the maximum motion of a low mode at moderate playing volume? Also, could you tell me once again the units of a radiation ratio? I tried to look it up but cannot find it.

I think you might find that the radiation ratio as used in sound radiation theory is something different than the RR they are talking about here. I think it is an "invention" by Schelleng to describe why spruce wood is a better and more efficient sound radiator than say maple.

In architectural acoustics we are more often dealing with the 'critical frequency', surface mass and thicknesses. I may return with some theoretical calculations on how sound reradiation may be affected by low versus high RR wood when I have access to the right software and more spare time for it. In some regions it is indeed possible to compensate for increased density by making the plates thinner, but the overall spectrum will be different.

The critical frequency will go up in frequency as the plate is thinned, is also goes up with lower sound speed wood, and it goes down by lower density of the plate. Bissinger make a case out of the critical frequency being lower for better instruments.

The critical frequency also sort of determines how well or efficieant the lower frequencies are radiating sound in an 'average over modes manner'. However if your plate becomes heavier or stiffer per surface mass, you are loosing vibration amplitude. There is a trade off between surface vibration velocity and sound radiation efficiency, at least in theory for flat plates. Curved plates are likely to behave similarly.

I am not quite convinced that a low density and high soundspeed is going to give the "eureka sound". I think it is possible to achieve the same spectrum and loudness by a different combination of construction and wood parameters. But that is an intuition and a hypothesis. Not all old italians have low density wood.

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I think you might find that the radiation ratio as used in sound radiation theory is something different than the RR they are talking about here. I think it is an "invention" by Schelleng to describe why spruce wood is a better and more efficient sound radiator than say maple.

In architectural acoustics we are more often dealing with the 'critical frequency', surface mass and thicknesses. I may return with some theoretical calculations on how sound reradiation may be affected by low versus high RR wood when I have access to the right software and more spare time for it. In some regions it is indeed possible to compensate for increased density by making the plates thinner, but the overall spectrum will be different.

The critical frequency will go up in frequency as the plate is thinned, is also goes up with lower sound speed wood, and it goes down by lower density of the plate. Bissinger make a case out of the critical frequency being lower for better instruments.

The critical frequency also sort of determines how well or efficieant the lower frequencies are radiating sound in an 'average over modes manner'. However if your plate becomes heavier or stiffer per surface mass, you are loosing vibration amplitude. There is a trade off between surface vibration velocity and sound radiation efficiency, at least in theory for flat plates. Curved plates are likely to behave similarly.

I am not quite convinced that a low density and high soundspeed is going to give the "eureka sound". I think it is possible to achieve the same spectrum and loudness by a different combination of construction and wood parameters. But that is an intuition and a hypothesis. Not all old italians have low density wood.

Yes, I asked my questions because I thought that for transverse waves one should look at per-area density and some kind of bending stiffness. Perhaps this reduces to bulk properties, but I was not convinced.

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does any of this really matter when a real violin will be varnished, which will change damping, Q, E etc. ? It seems to me that we can create almost any set of properties we want. The real question then becomes how can we make the composite behave as we want?

E constants are not likely to change much at all. Damping is a given for any system. The really REAL question is how to convince someone to buy a composite violin. Or how to get the cost of a good one down to $79.98

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Look at Curtin's article. I gave the link in another thread.

Radiation ratio (RR) has a well defined meaning and specific mathematical definition.

RR is the slope in Don Noon's great graph in the other thread, but you must be the the kilogram-meter-second (KGMS) system to get, say RR=15.

Don's plot used CGS units for the x-axis, and MKS for the y-axis, but that is OK. He labeled the slope in MKS units correctly. He knows what he is doing.

Mike

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does any of this really matter when a real violin will be varnished, which will change damping, Q, E etc. ? It seems to me that we can create almost any set of properties we want. The real question then becomes how can we make the composite behave as we want?

I don't think that varnish changes things as much as old violin literature would lead you to believe. When you initially apply varnish things do change a lot and measureably so. Once the oil/varnish hardens or solvents evaporate things seem to return to how they were before. On my most recent violin one of the first layers that I applied was a very thin coat of linseed oil. It did dampen the violin at first but after a few days in my living room window the oil hardened and it returned to normal. Same thing with the colored varnish, at first the varnish muffled the violin but after the solvent smell when away it went back to normal.

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If there is skepticism about the importance of material properties, then I suppose you could then build a perfectly acceptable violin out of lead. Spruce is used for soundboards because of its rather amazing material properties that are difficult to duplicate. It seems perfectly logical to me to select for those properties. What is not completely clear is which of the properties is most important, or if they have importance for different tonal characteristics. I have my ideas about it, but not much verification yet.

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Look at Curtin's article. I gave the link in another thread.

Radiation ratio (RR) has a well defined meaning and specific mathematical definition.

RR is the slope in Don Noon's great graph in the other thread, but you must be the the kilogram-meter-second (KGMS) system to get, say RR=15.

Don's plot used CGS units for the x-axis, and MKS for the y-axis, but that is OK. He labeled the slope in MKS units correctly. He knows what he is doing.

Mike

What is distracting is the term "radiation ratio." If the RR is what you say, that makes a definite statement about behavior of the vibrating mechanical systemin a vacuum. Radiatino and waves in air have notthing to do with it. It is the speed of sound in the wood, the elastic constants and density of the wood.. Acoustic radiation is a red herring, isn't it ?

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E constants are not likely to change much at all. Damping is a given for any system. The really REAL question is how to convince someone to buy a composite violin. Or how to get the cost of a good one down to $79.98

The 'net' E increases quite a bit across the grain when a violin top plate is varnished and dry.

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I don't think that varnish changes things as much as old violin literature would lead you to believe. When you initially apply varnish things do change a lot and measureably so. Once the oil/varnish hardens or solvents evaporate things seem to return to how they were before. On my most recent violin one of the first layers that I applied was a very thin coat of linseed oil. It did dampen the violin at first but after a few days in my living room window the oil hardened and it returned to normal. Same thing with the colored varnish, at first the varnish muffled the violin but after the solvent smell when away it went back to normal.

William,

Sorry I can't locate the link right now, but I am certain that Martin Schleske (might have been published in The Strad) found that lower damping increases the sound output and makes the response curve have higher, sharper peaks. With no vibrato, this would be problematic, but vibrato increases the complexity and beauty of the tone. He found several ground substances that minimized damping, but he did not say what they were. That's also what the fungus treatment does.

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Curtin used the term "radiation ratio" in his tap tone article. To be comparable with his numbers, everything needs to be in units of meters, kilograms, and seconds.

Radiation ratio has absolutely nothing to do with damping. It is essentially a measure of stiffness and density only.

Don,

You are chipping away at my core beliefs (in violin making). I have no formulae right now. But I am certainly going to go back and think this over.

When you "cook" a piece of wood, are you not increasing the stiffness and lowering density? How would you measure stiffness alone?

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If there is skepticism about the importance of material properties, then I suppose you could then build a perfectly acceptable violin out of lead. Spruce is used for soundboards because of its rather amazing material properties that are difficult to duplicate. It seems perfectly logical to me to select for those properties. What is not completely clear is which of the properties is most important, or if they have importance for different tonal characteristics. I have my ideas about it, but not much verification yet.

I am not skeptical about the importance of material properties, only skeptical about which properties we should be concerned about. I think that when most everyone (but not unanimously) says they hear a difference between their violins in the white, and the same violin varnished, we should have greater concern for the wood/varnish composite. Sam Z says he wants a ground to "glue all those fibers together" and give the sound a "sizzle." Seems to me that there should be a concern primarily for cross grain E when varnished. I suspect that along grain E doesn't change too much with varnish, but I have never measeured it. IIRC, Schleskes measurements of the effects of varinish are only for cross-grain properties.

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When you "cook" a piece of wood, are you not increasing the stiffness and lowering density? How would you measure stiffness alone?

So far, my cooking process reduces stiffness AND density... but at about nearly the same rate. This results in about the same speed of sound, but a higher radiation ratio (and some damping changes). I don't measure stiffness alone... I measure the free-free bending mode frequency, dimensions, and weight. The equations are well known to back out the the stiffness from these measurements.

I suspect that along grain E doesn't change too much with varnish, but I have never measeured it. IIRC, Schleskes measurements of the effects of varinish are only for cross-grain properties.

Along the grain, the wood is extremely stiff, so varnish doesn't have that much effect. Crossgrain stiffness is typically only 10% as much, so the varnish has a much more pronounced effect. I HAVE measured it for a variety of surface treatments. In all conditions (natural, processed, varnished), crossgrain properties appear to be the most variable and easily affected. This has to be of some importance to instrument acoustics, but it is not yet clear how important it is or what the effect is. The vast majority of the attention is focused on along grain properties (which I'm sure is of primary importance), but it certainly isn't the whole story.

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  • 3 weeks later...

I gave the specific design info of the ultrasound meter to a Chinese company and they told me they would make the equipment available to us soon. They can easily convert on-the-shelf thickness meter technology for our purpose. The pulse needs to be strengthened to drive the low frequency transducers. The transducers are made of several PZT ceramic discs stacked together in opposing polarity. The meter will display time-of-flight in micro-second. The software will fit the exponential decay curve to the signal attenuation to yield damping factor.

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Now Bill, I empathize with your situation. In fact, I too have been known to introduce controversy from time to time for attempting to inject humour. The general solution to this ongoing problem is merely to be more subtle in the choice of words, rather than abort the mission.

For example, had you instead said “Is this a Freudian slip, or has an abundance of fatty tissue accumulated within the vicinity of your distal and proximal interphalangeal joints?” I am sure everything would have been just fine.

Perhaps "fatty tissure" seems a little threatening. I think "adipose tissure in the dermis" would be more elegant.

:)

Rick Draganowski

(Soli Deo Gloria)

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I gave the specific design info of the ultrasound meter to a Chinese company and they told me they would make the equipment available to us soon. They can easily convert on-the-shelf thickness meter technology for our purpose. The pulse needs to be strengthened to drive the low frequency transducers. The transducers are made of several PZT ceramic discs stacked together in opposing polarity. The meter will display time-of-flight in micro-second. The software will fit the exponential decay curve to the signal attenuation to yield damping factor.

Thank you David.

Rick Draganowski

(Soli Deo Gloria)

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Along the grain, the wood is extremely stiff, so varnish doesn't have that much effect. Crossgrain stiffness is typically only 10% as much, so the varnish has a much more pronounced effect. I HAVE measured it for a variety of surface treatments. In all conditions (natural, processed, varnished), crossgrain properties appear to be the most variable and easily affected. This has to be of some importance to instrument acoustics, but it is not yet clear how important it is or what the effect is. The vast majority of the attention is focused on along grain properties (which I'm sure is of primary importance), but it certainly isn't the whole story.

I think I have a filler-sealer that should have a very low effect on cross-grain stiffness. Of course, overlain varnish might increase this. Would you be willing to send me a wood sample which you have measured crossgrain, allow me to seal and fill myself? I will then put on a couple ground coats. Then it would be interesting to compare the result with any process that you use.

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