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Tap tone test , top plate


Arsalan
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3 hours ago, Shunyata said:

 Indeed, violins are not bells!

2 hours ago, Michael Darnton said:

I think of the violin as a speaker cone

Agreed that a violin is not a bell... and it definitely is not a speaker cone, either (that's the concept I started with and abandoned when learned more).  And a violin is not a free plate.

However, neither is a violin magic.  It has to follow the laws of physics and acousics, just as bells and speakers do... although they all are very different in the way they vibrate, how the laws apply, and the goal of the design.

The complexity of the violin acoustics and the lack of well-defined acoustic goals make best suited for inherited tradition and trial-and-error construction.  That has been going on for a very long time, and works well.  However, that is not a reason to totally abandon actual physics and acoustics analysis (not arm-waving or thought experiments), which could lead to better understanding and therefore more consistent results that the maker intends to get.

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28 minutes ago, Don Noon said:

Agreed that a violin is not a bell... and it definitely is not a speaker cone, either (that's the concept I started with and abandoned when learned more).  And a violin is not a free plate.

However, neither is a violin magic.  It has to follow the laws of physics and acousics, just as bells and speakers do... although they all are very different in the way they vibrate, how the laws apply, and the goal of the design.

The complexity of the violin acoustics and the lack of well-defined acoustic goals make best suited for inherited tradition and trial-and-error construction.  That has been going on for a very long time, and works well.  However, that is not a reason to totally abandon actual physics and acoustics analysis (not arm-waving or thought experiments), which could lead to better understanding and therefore more consistent results that the maker intends to get.

When I was crewing on a sail-powered racing boat, I took one of my hyper-cavitating engine powered propellers to the skipper of the boat, who happened to be a Ford powertrain engineer, highly involved in fluid dynamics with the transmission hydraulic "torque converters". He told me that it looked pretty good, but that development beyond that point would pretty much come down to trial and error.

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A speaker is a better analogy for a violin than a bell or marimba, but it still isn't very good.

Both a violin and a speaker are transducers umtimately radiating a driving signal into the air.  But the analogy breaks down there.

A good speaker is made so it's entire operating surface will be driven as one by the signal.  Often, a small center portion is distinct and can be regarded as the actual speaker for higher frequencies.  But, the idea is driven motion as one surface, without breaking up into patches of different phase.  More complex speakers are arrays of such simple speakers.

This does not at all carry over to violin family instruments.  These instruments break up into patches of standing waves depending on the frequencies from the driving signal.  Only for the lowest frequencies do these standing waves move large portions of the whole plate giving a limited resemblance to speaker behavior.

Further, the front, the back plate, the sides and body structure together, and the air inside all provide flexing masses that can form standing waves.  Each of these are important at various frequencies.  And couplings between these are important.

To make things more complicated, these mass also have natural resonances, which end up coloring the balance of the standing wave responses to the driving signal.  (This is the part tap toners over focus on and often pretend is the full or dominent story).  In contrast, speaker designers try to avoid resonances that might color response.

Violin plates are mostly soundboards.  But, for some modes and frequiency ranges they partially behave somewhat speaker like.  And then their are air modes and couplings.

It's complicated.

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Mo'ooom not the speaker cone again, ...fwiw I understand MD, but I have now come to find "speaker cone" is a trigger word in violin land, as we see by the responses, and you just can't say it because it's just "too interpreted" as disinformation :rolleyes:....even though you weren't saying it acts or functions like one, people still insist that's what you meant, just because you said one of the many now words that we do not speak. So lets just do everyone a favor and not say "the s word"  

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2 hours ago, David Beard said:

I find the idea of some loose analogy to speakers much less off putting than the rampent idea that precise 'high Q' tap tones are good or relevant.

Yes Q is another word you can't say, even though it's just a letter

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4 hours ago, David Beard said:

A speaker is a better analogy for a violin than a bell or marimba, but it still isn't very good.

Both a violin and a speaker are transducers ultimately radiating a driving signal into the air.  But the analogy breaks down there.

A good speaker is made so it's entire operating surface will be driven as one by the signal.  Often, a small center portion is distinct and can be regarded as the actual speaker for higher frequencies.  But, the idea is driven motion as one surface, without breaking up into patches of different phase.  More complex speakers are arrays of such simple speakers.

 ( ... )

It's complicated.

It is.

I sit in a room with over 20 pairs of loudspeakers. I just had lunch of tomatoes, mozarella, OO, herbs and vodka shots with a friend who brought the vodka. Though it obliterated the food, the vodka was satisfying.

It's been a very tough year. A year where kids virtually lost a full ( two? ) year of close instruction. Some of the performances attended were ghostly shells of abstractions of what was taught in the 1970s. Some did well. Most appeared a but lost, distant. So it goes.

The room has four sets of 7.2 theatre systems from around the world, not Japan or America as there are plenty to hear locally. My 5th, an Italian set are in split up in storage as there is no longer a center channel. The whole home theatre system is very strange when the center ( dialog ) speaker is afforded the most information.

In another room, there are a few guitar and bass cabinets with papers cone speakers. Depending on the crossover points, speakers in High- Fidelity systems try to "behave" within their frequency ranges. In a piston- like motion or with primary break up points are known nodes. Electric guitar speakers and some electric bass speakers operate full range. 12" speakers should theoretically not behave very well in the upper octaves. Actually, they do not operate "accurately" above the 12th fret high e- string. It's mostly chaos, really.

Add distortion, or not. Let the speaker add distortion.

Cone "break up" theoretically is the golden fleece of guitar sound. It did not occur unless the amplifier is turned up to an ungodly, profoundly level. The unique distortion produced from the structural breakup of the cone created hot and live artifacts which were distortions, apart from overdriven tubes or distorting amplifiers. Pinholes, putty, sub- structures, were used to try to control the chaos.

The top experiences "breakup." The Strad 3D, however esoteric is fun. My second copy has not been returned. I have lent out three copies of the Henley never to be returned. An angel in a dream whispered that I did not need them. Just because I act relaxed does not mean that you can have my stuff.

I listen to tap tones, even measure them, but given an input the low frequencies are of more interest.

As for speaker drivers, the interested is in the low frequency output of given a form. The closest we can get a <25mm speaker to produce lower frequencies, in somewhat a linear fashion, phones, pads and laptops sound better. 

Bookshelf speakers are about the only things people are buying. Full range? It's like burning harpsichords.

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3 hours ago, David Beard said:

I find the idea of some loose analogy to speakers much less off putting than the rampant idea that precise 'high Q' tap tones are good or relevant.

Not that we need to discuss anything in tech, but the control systems were the rage about twenty- five years ago pre- internet explosion. The subject can be off putting to old timers.

A stiff, well behaved piece of wood is pretty cool. I would love to purchase any if they are available.

But there are questions. And I read your posts intently.

Why are older instruments the way they are? I tend to like European wood, no matter how new, over American. Given similar behaviours, those are my preferences.

Lately, my limited experience is with older Pernambuco. Just recently started ( like two years ago ) a bow( s ) where I mounted a frog before the bow was cambered and fully faceted. Just listening to tonal characteristics. Trying to reverse engineer some answers? The bow that behaves better, sounds better. They are like long cello bows but feel like tree trunks. But they sound different. Yes, all three are from an unremarkable plank. 

There are the master makers that can make winners from milk cartons or wet rags. They have their approach. Sometimes the myth is around the genius, while others is in their flexibility. I once got a Mr Spock eye brow lift from a maker when I observed an "anomoly" in their graduation in mixed company. Despite marking me a "dumass" in utter silence in front of those in the know, it made it clear that he understood the wood better than I did the whole instrument.

I like ring, but control can also be valuable.

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8 hours ago, David Burgess said:

When I was crewing on a sail-powered racing boat, I took one of my hyper-cavitating engine powered propellers to the skipper of the boat, who happened to be a Ford powertrain engineer, highly involved in fluid dynamics with the transmission hydraulic "torque converters". He told me that it looked pretty good, but that development beyond that point would pretty much come down to trial and error.

Jet engine turbine blades can't really be designed by trial-and-error, and they operate in some of the most complex environments you could imagine.  But there's big $$$ in jet engines, so the ultimate in computational fluid dynamics can be employed.  But there are also quantitatively definable goals.  Violins have neither that level of $$$ or difinable goals, although I'm sure modern technology could model the physics and acoustics well.  It's complicated, but not impossible... but also expensive and pointless if you don't know the goal.

8 hours ago, Michael Darnton said:

@Don Noon I'm not sure you understand my analogy, because it's an analogy, not a model. I am not saying that a top moves like a speaker cone.

Correct me if I'm wrong, but you have repeatedly touted the idea of non-resonances and lack of "ring" as some kind of goal to let the "signal" from the player come through without being perturbed... something like the goal of speakers.

What you describe can be perfectly achieved by an electric violin.  It is all of the modes and various ring levels that give the acoustic violin its characteristic sound and dynamics.

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37 minutes ago, John_London said:

Of course a violin is magic.

Well ya duh'! all one need do is apprentice under their own local wizard and use the charm of making.... Anál nathrach, orth’ bháis’s bethad, do chél dénmha , Anál nathrach, orth’ bháis’s bethad, do chél dénmha, Anál nathrach, orth’ bháis’s bethad, do chél dénmha...

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17 hours ago, Shunyata said:

Being an engineer by profession, I started with a quantitative bent toward violin making.

There are a few first order principles (<65g, not too thin in a couple critical areas, etc.) that make a huge difference.  Past that, the nuances of each individual piece of wood become significant factors and experience is essential for assessing and responding to those nuances.

One thing I had to let go of is the notion that wood or plates should "ring".  Indeed, violins are not bells!

Hi there 

I’m a mechanical engineer too and I am getting very interested in violin making .. may I ask which area are you referring to? As not to be too thin ? 
center ? And edges ? Or bouts ?

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I've been re-reading the 2006 thread "Cremona versus the rest". The Strads which practically play themselves, the DG Cannone which few players can make sound good.  All doubtless fantastic violins. Then there are good but lesser violins which practically play themselves but with limited colour potential. Which are you tapping for?

5 minutes ago, Arsalan said:

Hi there 

I’m a mechanical engineer too and I am getting very interested in violin making .. may I ask which area are you referring to? As not to be too thin ? 
center ? And edges ? Or bouts ?

As someone who has handed over cash for a new violin not very long ago, I am asking different questions. Is the wood thick enough and stable enough that the arch will not sink, the plates will not crack, and less seriously, there is a low risk of seams opening? Is the instrument at once robust, yet light and balanced and alive in the hand, and quite floaty under the chin even without a shoulder rest (think Milstein videos). You have to feel comfortable with it, in so far a violin is ever comfortable. Does it look nice? If it is copy, does the grain look like the original? Certainly there are sonic properties to the box, as well as the setup and the bow, but no single criterion. So I am not sure what makers are looking for when they tap?

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6 hours ago, Don Noon said:

Jet engine turbine blades can't really be designed by trial-and-error, and they operate in some of the most complex environments you could imagine. 

There is no refinement of turbine blades via experimentation and testing? They just design the thing via calculations, consider it done, and put it into service?

A lot of the efficiency improvements of super-cavitating propellers has come from actual testing and measuring of things like like shaft torque versus thrust, and observation of erosion patterns. Or by putting several design concepts on a boat, and seeing which makes the boat go faster.

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I think I have mentioned before that I know a STRAD with harlequin top *and* back to the extent that I had to put the main light on one side above the instrument and the other side below to make them the approach same brightness for photos, and this was a universal fave of the many who got to play it. So I'm going to say it doesn't make a bit of difference, tonally.

Or maybe it is even positive.

I've made a few with more runout than most would tolerate with no evil effect.

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12 minutes ago, Michael Darnton said:

I think I have mentioned before that I know a STRAD with harlequin top *and* back to the extent that I had to put the main light on one side above the instrument and the other side below to make them the approach same brightness for photos, and this was a universal fave of the many who got to play it. So I'm going to say it doesn't make a bit of difference, tonally.

Or maybe it is even positive.

I've made a few with more runout than most would tolerate with no evil effect.

That is encouraging because the top I am currently working on has quite a bit of runout...

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55 minutes ago, scordatura said:

Anyone want to speculate on the effects of runout on tops?

Fact:  it's more annoying to carve and scrape, if the runout is at the centerline and goes in opposite directions.  Also there's going to be runout somewhere (relative to the surface) due to arching... with normal carved plates.

Other than that, sonically, I would guess not much for small angles.

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