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A0 mode: What is more important air mass or frequency?


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This is another sideline from my new concept (super light) violin thread.

The latest development made me really scratch my head, because the reduction of 2mm changes the frequency only 6Hz and this not even a half note in this region rather something like 1/3 note. Despite, the change in sound quality was very noticable and I started to ask myself: Why?

On a second thought I calculated the reduction in the actual air volume and this came down to roughly 6%. 

There is no question that the air mode frequency makes a sound difference, but from all I know this is only in the region of its own frequency. It is for me hard to imagine that this can have an impact on the whole playability of the instrument. My rough guess is that it makes a measurable difference how much mass the vibration of the top has to move especially when the top is very thin. Calculating the actual weight of the inside air (something around 1.6g) this sounds a bit ridiculous, but for the moment I have no better explanation

Any other thoughts on this or has there ever been done research on top weight/stiffness versus contained air weight?

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22 minutes ago, Andreas Preuss said:

Despite, the change in sound quality was very noticable and I started to ask myself: Why?

You haven't described what quality in the "sound quality" has changed.  I seriously doubt that anything related to A0 would make a big change to perceived sound quality, other than perhaps the roundness and location of C# on the G string.

I'm guessing the reduced air volume does something to the higher frequencies, like getting more of the higher frequency energy to come out of the soundholes.  I recall experimenting with opening up F-holes, with similar effects.  If the volume was infinite, there wouldn't be anything coming out of the soundholes, other than some diffraction around the edges.

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35 minutes ago, Andreas Preuss said:

This is another sideline from my new concept (super light) violin thread.

The latest development made me really scratch my head, because the reduction of 2mm changes the frequency only 6Hz and this not even a half note in this region rather something like 1/3 note. Despite, the change in sound quality was very noticable and I started to ask myself: Why?

On a second thought I calculated the reduction in the actual air volume and this came down to roughly 6%. 

There is no question that the air mode frequency makes a sound difference, but from all I know this is only in the region of its own frequency. It is for me hard to imagine that this can have an impact on the whole playability of the instrument. My rough guess is that it makes a measurable difference how much mass the vibration of the top has to move especially when the top is very thin. Calculating the actual weight of the inside air (something around 1.6g) this sounds a bit ridiculous, but for the moment I have no better explanation

Any other thoughts on this or has there ever been done research on top weight/stiffness versus contained air weight?

Did you also shorten your sound post 2mm?

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1 minute ago, Don Noon said:

You haven't described what quality in the "sound quality" has changed.  I seriously doubt that anything related to A0 would make a big change to perceived sound quality, other than perhaps the roundness and location of C# on the G string.

I'm guessing the reduced air volume does something to the higher frequencies, like getting more of the higher frequency energy to come out of the soundholes.  I recall experimenting with opening up F-holes, with similar effects.  If the volume was infinite, there wouldn't be anything coming out of the soundholes, other than some diffraction around the edges.

Ok a better description:

First of all the noticable over resonance between A and Bflat on the G string disappeared. This is probably not so much a miracle since the air resonance shifted up.

The miracle is to me a sort of increased 'sound density' or you could also say 3 dimensional sound as perceived under the ear. While very cheap instruments always sound 'meager' better violins sound already fuller or 2 dimensional. The latest progress on the new concept violin made it from 2 dimensional (with some minor defaults) to 3 dimensional (with no audible defaults). the sound became noticeably richer.

I wished I could come over to your shop to make a discussion with the instrument at hand. 

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3 minutes ago, Marty Kasprzyk said:

Did you also shorten your sound post 2mm?

Well, I had to.

Other things affected to the rib reduction are a different leverage at the neck heel on the body. But I have experimented with that too and didn't find any audible differences.

Then of course the linings on the back were reduced in height from 8mm to 6mm. There again, a previous test has shown that changeing the initial micro linings (1mm x 2 mm triangular shape) to strad type standard linings didn't change very much. It was more the sort of 'timbre-shift'.

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My take is that the specific frequency doesn't matter, much.  And that the more specific you make the frequency the worse.

The greater or lessor the air mass (proportional to air volume) the more or less energy can fall into this resonance, and later potentially radiate out from it.

And this connects to the depth of tone of instrument.  If you want more of the playing energy to fall into the lower tones, then more air mass to soak in more low energy.  If you want a brighter instrument, then less air mass so less energy can store here.

 

But what is truly not looked at enough is how broadly this air mass responds.   You want it to be a  somewhat low Q, not at all like a helmholtz bottle that responds very specifically at X frequency and then falls off sharply on either side.  No, you want it to respond to a band of frequencies around X.  The broader the better.

And you want it to respond to a band around 2*X, around 3*X, around 5*X. And more if possible.

 

In my not carefully thought through initial opinion.

 

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You might be jumping into conclutions about the "changes" after a modification?

My experience is that modifications made, that you observe as an immediate impact, many times goes back to the original state, after  some days or even weeks.

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11 hours ago, Andreas Preuss said:

This is another sideline from my new concept (super light) violin thread.

The latest development made me really scratch my head, because the reduction of 2mm changes the frequency only 6Hz and this not even a half note in this region rather something like 1/3 note. Despite, the change in sound quality was very noticable and I started to ask myself: Why?

On a second thought I calculated the reduction in the actual air volume and this came down to roughly 6%. 

There is no question that the air mode frequency makes a sound difference, but from all I know this is only in the region of its own frequency. It is for me hard to imagine that this can have an impact on the whole playability of the instrument. My rough guess is that it makes a measurable difference how much mass the vibration of the top has to move especially when the top is very thin. Calculating the actual weight of the inside air (something around 1.6g) this sounds a bit ridiculous, but for the moment I have no better explanation

Any other thoughts on this or has there ever been done research on top weight/stiffness versus contained air weight?

My rough guess is that the lowering of the ribs could have an overall influence on the flexibility of the body, which could be a more important factor than the change in air volume on the response of the violin.

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7 hours ago, David Beard said:

But what is truly not looked at enough is how broadly this air mass responds.

I think so too.

And from what I have seen with my experiments the tonal result depends much on the thickness and mass of the top when the rib height is increased or decreased.

In the making process this is IMO a very useful procedure to calibrate the sound timbre in a final stage. 

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37 minutes ago, Davide Sora said:

My rough guess is that the lowering of the ribs could have an overall influence on the flexibility of the body, which could be a more important factor than the change in air volume on the response of the violin.

You mean it is getting stiffer when lowering the ribs?

Then we would probably look on a double effect which shifts the overall sound timbre from alto voice to soprano voice.

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3 hours ago, Andreas Preuss said:

You mean it is getting stiffer when lowering the ribs?

Then we would probably look on a double effect which shifts the overall sound timbre from alto voice to soprano voice.

My guess is that by lowering the ribs the body becomes more flexible longitudinally and torsionally, but that the stiffness increases in the breathing modes where the plates change in width crosswise during motion.

Can it make sense?

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There was an experiment done at Oberlin one year where a fine maker chose to cut the ribs, I think about 5-7mm, on a viola. There was a slight difference but I think we had problems finding clear differences in the spectra. 

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Like everything in a violin, each detail actually touches many out comes in complicated ways.

We just don't get to move one variable without many things changing.

This is way I'm placing my bets and effort on returning to old ways.  Their community learning was highly collective and continous over generations of development.  

Our modern efforts to learn and improve are by comparison very disjunct and isolated.   We might explore an idea across tens of iterations.  But our units of change are usual too big and radical.  So they exist in separate little islands.

The classical development in contrast was collective, and proceeded in very incremental units of change, across generations and thousands of iterations.

For such a holistic object as a violin, where each part touches so many outcomes, their approach has great advantage.

When we come to Strad, Del Gesu, and even Gii Amati, Montagnana, Seraphino, et al.; they're standing on a great mountain of accumulated continous collective learning.

Too bad the continuity of culture broke circa 1750-1776.

My bet is that 'low iteration', 'big unit of change' modern efforts to improve violins are going to continue to be interesting but inbalanced in outcome for a long while.

That's why I believe the best road is to resume their methods, continously from their works of around 1710 to 1740.  If this becomes possible, then a small community of such new makers could also resume their slow collective approach to development.

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19 hours ago, Andreas Preuss said:

The latest development made me really scratch my head, because the reduction of 2mm changes the frequency only 6Hz and this not even a half note in this region rather something like 1/3 note. Despite, the change in sound quality was very noticable and I started to ask myself: Why?

There might have been a difference from just taking it apart and glueing it togehter again and set it back up with strings. The ribs are a bit special, including cardboard.

There is an effect of the plate stiffness on the A0 frequency, the height and roundness of the f-hole edges, as well as the volume. A true Helmholz resonator have stiff walls, and are basically an air plug with a given mass (dependant on the area of the hole or f-holes and their depth as well as «end corrections», the holes are deeper than just the hole sides as the air in action both a bit outside and inside of the holes). Theoretically the frequencuy dependence goes as volume^0,5 being the spring of the resonating system. Including the plate stiffness and coupling to the nearest other mode A1 it decreases somewhat as described by Marty. I think Bissingers rule come from the Octet set of Hutchins and not from violins alone, so it may be used with some care. He did analyse this in an aluminium model with varying volume though, many years ago.  

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Anders,

Every time you post (lately not too often...)- I read! (and sometimes post contradictional posts)

Ok, du förstår.... men varför tänker du att de "get it" ."?."...

Eller?

Jag är Finnen som inte förstår "anything".......

 

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Hi Anders,

When Carleen Hutchins and John Schelleng designed and built the original set of their Octet instruments the A0 frequencies for their large bass, small bass,  baritone, and tenor were all much lower than they wanted so they cut down their rib heights a lot to increase their A0 frequencies.

I've plotted the % increase in A0 frequency vs. the % of rib height reduction which is shown in the attached graph. I've projected those four data points down to zero which is shown by the straight line which has a slope of 0.33 so one percent of rib height gives only 1/3 percent increase in A0 frequency.

George Bissinger has later done considerable experiments on the AO frequency when the volume of an aluminum violin is changed by filling it with water to various amounts.  He found the A0 frequency is inversely proportional to the volume to the 0.27 power.  That is also plotted in the same graph as grey dots which is very similar Hutchins data projection.

Screen Shot 2021-05-14 at 3.56.12 PM.png

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25 minutes ago, Marty Kasprzyk said:

Hi Anders,

When Carleen Hutchins and John Schelleng designed and built the original set of their Octet instruments the A0 frequencies for their large bass, small bass,  baritone, and tenor were all much lower than they wanted so they cut down their rib heights a lot to increase their A0 frequencies.

I've plotted the % increase in A0 frequency vs. the % of rib height reduction which is shown in the attached graph. I've projected those four data points down to zero which is shown by the straight line which has a slope of 0.33 so one percent of rib height gives only 1/3 percent increase in A0 frequency.

George Bissinger has later done considerable experiments on the AO frequency when the volume of an aluminum violin is changed by filling it with water to various amounts.  He found the A0 frequency is inversely proportional to the volume to the 0.27 power.  That is also plotted in the same graph as grey dots which is very similar Hutchins data projection.

Screen Shot 2021-05-14 at 3.56.12 PM.png

Marty,

We are too retarded to understand........

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48 minutes ago, Marty Kasprzyk said:

Hi Anders,

When Carleen Hutchins and John Schelleng designed and built the original set of their Octet instruments the A0 frequencies for their large bass, small bass,  baritone, and tenor were all much lower than they wanted so they cut down their rib heights a lot to increase their A0 frequencies.

I've plotted the % increase in A0 frequency vs. the % of rib height reduction which is shown in the attached graph. I've projected those four data points down to zero which is shown by the straight line which has a slope of 0.33 so one percent of rib height gives only 1/3 percent increase in A0 frequency.

George Bissinger has later done considerable experiments on the AO frequency when the volume of an aluminum violin is changed by filling it with water to various amounts.  He found the A0 frequency is inversely proportional to the volume to the 0.27 power.  That is also plotted in the same graph as grey dots which is very similar Hutchins data projection.

Screen Shot 2021-05-14 at 3.56.12 PM.png

Looks great, and a nice recapitulisation. Reducing the A0 frequency by 20 Hz, or almost 10%, would take a 30% rib reduction then. If it is 30mm it would be 9mm. Easier to fill in the f-holes then. I did that in one intrument I had too open holes, not easy to do.

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I've lived in Colorado Springs for 50+ years and had the pleasure of hearing Zukerman, Perlman, Bell, Barton-Pine, Chang and others  perform with our local symphony.  Our elevation is 6,000+ feet downtown where all performed.  Atmospheric density here is about 1.0 Kg/M^3 compared to 1.2 at sea level.  None of the violin super-stars complained of their fiddles sounding funny due to a change in A0.  All of them sounded to me just like their recordings, the most likely locations for the recordings being made was in large cities, the majority of which are at sea level.  If this makes a difference it will take much better ears than mine to hear it.

 

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1 hour ago, Anders Buen said:

Looks great, and a nice recapitulisation. Reducing the A0 frequency by 20 Hz, or almost 10%, would take a 30% rib reduction then. If it is 30mm it would be 9mm. Easier to fill in the f-holes then. I did that in one intrument I had too open holes, not easy to do.

I agree --bigger f  holes are better.

Claudia Fritz (attached paper) found that it takes about a 20% change in A0 frequency to be even detectable. But If you change the amplitude of A0 it takes only about 10% change to be detectable.   George Bissinger (attached paper figure 4) found the a big difference between "bad" and "good" violins was that good violins had a higher amplitude A0. 

One way of increasing the A0 amplitude is to increase the f hole open area.  Thus increasing the size of the f hole opening might be a better way of increasing the A0 frequency (not very important) than decreasing the rib height.

 

Fritz--perception of changes.pdf Bissinger, directivity.pdf

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Roger, first order is that the A0 won't be any different at altitude, assuming a normal room temperature.  Speed of sound is the releveant variable in calculating a cavity resonance...

Air pressure has no effect at all in an ideal gas approximation. This is because pressure and density both contribute to sound velocity equally, and in an ideal gas the two effects cancel out, leaving only the effect of temperature. (Ref:  https://www.sciencedaily.com/terms/speed_of_sound.htm)

However, there might be a small second-order effect, as the wall stiffness (assumed to remain the same) may be relatively more rigid in the net mass/spring calculation.  I can't imagine it would be any more than a few Hz, not a big deal.

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2 hours ago, Peter K-G said:

Marty,

We are too retarded to understand........

The difference between knowledge and wisdom:

Knowledge is knowing that a tomato is a fruit.

Wisdom is knowing that you shouldn't put a tomato in a fruit salad.

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12 minutes ago, Bodacious Cowboy said:

The difference between knowledge and wisdom:

Knowledge is knowing that a tomato is a fruit.

Wisdom is knowing that you shouldn't put a tomato in a fruit salad.

I'll give it a try.  

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