Measuring the acoustic behaviour of the closed soundbox- a better method to predict the sound?

[Andreas Preuss]

This is another side line to my thread about the New Concept Violin. 

 

The problem of making precise predictions on the sound of the finished violin comes basically from the fact that they will be assembled to the soundbox where the single parts influence each other. So logically measurements on the assembled sound box should be able to tell us all (?) or most of the things we need to know?

Is there any research on this or is anyone here who is making assessments by tapping or whatever method he/she is using?

(I will be away for a week, so sorry if I can’t answer any questions/ideas/suggestions)

[MANFIO]

I remember Sacconi mentioned a given note to Strad's violins when we blow in the f-holes. But that is too little. Interesting approach! Some info would be useful. 

[Don Noon]

I have often taken frequency response of a closed body alone, trying to get an early read on any issues that might need to be fixed.  Body is suspended by rubber bands, and hammer taps at where the bass foot will eventually be.

1.  The neck and chinrest make a big difference in the signature modes... so I have put on a chinrest, and added some spool clamps to the upper block area to simulate the neck mass.  That puts the frequencies closer to the final value, but the amplitudes vary a lot.  The frequencies are "closer", but still vary significantly from the final values.  Even A0 will change due to the bridge and string mass.

2.  The higher frequencies don't tell you anything useful, as it all changes when the bridge and strings are in place.

I have also used a voice coil driver to play music through the body.  There's nothing quantitative from this, but if it doesn't sound horrible, I figure it's OK to keep going.

I suppose if you had carefully calibrated spectra from the body and the completed violin, and lots of data from lots of violins, you might be able to make some rough correlations from one to the other.  Or maybe not.  For me, once the body is together I'm going to finish it as-is anyway, and if something needs fixing, I'll fix it when I can play it for real later.

[Andreas Preuss]

@Don Noon

’or maybe not’ 

In total this sounds like ‘too much work with too little chances of success. 

regarding 1: 
I got some doubts if signature modes are so important altogether. I think they got so much focus because they are easily measurable and some ‘interesting’ relationships could be found plus some methods to trigger them. Getting all signature modes ‘right’ is no receipe for the sound and playing properties high class players are looking for. (IMO PK made unwillingly the proof for that with signature modes ‘dead on’ and the rest ‘whatever’) 

Regarding 2: 
When it comes to high frequencies (and their behaviour under bowing conditions) I think they are by far more important to separate good and bad violins and they get not so much attention because no significant resonances can be singled out for acoustic investigations. The fact that they change in a rather uncontrollable way with completing the instrument just shows that trying to ‘calculate’ anything before is more or less useless. 

This confirms my basic idea that violin structures which can be calibrated after setup are basically the easiest and most practical way to sculpture the sound. In this sense I think that the New Concept violin incorporates a completely new approach because the top arch can be altered together with the string angle for this purpose  after setup, something almost impossible on the traditional construction method. I firmly believe that creating a new model alone is no receipe for success but rather a new approach in adjusting the sound in all possible aspects. So, compared to the classic approach this means: less time for building the structure itself and more time to adjust the structure for optimal ‘sound function’.

 

[Salve Håkedal]

I have been tapping and recording frequencies for over 10 years (100+ instruments) in many stages; from wood billets to the set up instrument. I find it interesting. But how useful it has been is hard to say. What I do know, is that is has prevented me from developing badly funded and possibly harmful pet theories. And that's good!

Beware: I'm no scientist and my measuring methods/routines are sloppy.

Below is a plot of a hardangerfiddle. For "No neck" and "With pegs" I tapped where the left bridge foot will come. For "Fully set up" I tapped from the side to the top of the left bridge edge.

(Hardangerfiddles usually have thinner strings as well as somewhat thinner plates than most new violins. I don't think the added sympathetic strings takes the total string tension up to the tension of a normal violin string set.)

 

[David Burgess]

Andreas, might George Stoppani's investigations and modeling methods come the closest to what you are looking for? He has done a lot of modeling and measuring of the ways that parts of a violin, and assembled violins actually move to produce sound, and has designed his own software to assist in doing so.

An example of the sort of work he does:
https://www.youtube.com/watch?v=jkv-eoHN58c

Whether or not greater knowledge of such things will easily enable one to make better violins, I do not know.

[Don Noon]

2 hours ago, David Burgess said:

...George Stoppani ...has done a lot of modeling and measuring of the ways that parts of a violin, and assembled violins actually move to produce sound, and has designed his own software to assist in doing so.
...
Whether or not greater knowledge of such things will easily enable one to make better violins, I do not know.

It's one thing to know the mode shapes and frequencies, but another thing entirely to actually use that knowledge to adjust the sound.  I tried it a few times, trying to quiet down a mode around 1 kHz that was annoyingly loud.  I got the mode shape to change a bit, but it was still around the same frequency and loudness.  You might notice the lack of publications demonstrating effective use of modal information to make targeted changes to a response spectrum.

I have been taking response spectra of white bodies for a while (it's not that much extra work), and  I have seen wide variations that looked frighteningly different.  Fortunately I avoided the temptation to try to make it "better" at that stage, because after assembly, they all turned out similarly fine.

[David Burgess]

40 minutes ago, Don Noon said:

It's one thing to know the mode shapes and frequencies, but another thing entirely to actually use that knowledge to adjust the sound. 

Yup. Therein lies the pickle.

Maybe it's a matter of observing everything that can be observed, and using that as the foundation for letting the imagination go wild?

[Don Noon]

16 minutes ago, David Burgess said:

Maybe it's a matter of observing everything that can be observed, and using that as the foundation for letting the imagination go wild?

After everything has been observed, the universe has collapsed into the next Big Bang and erased everything from this cycle.

I'm more interested in getting the next instrument done in my lifetime.

[David Burgess]

2 minutes ago, Don Noon said:

After everything has been observed, the universe has collapsed into the next Big Bang and erased everything from this cycle.

I'd been thinkin' we had quite a bit of time left before that happens. But you would know more about such things than I.

4 minutes ago, Don Noon said:

I'm more interested in getting the next instrument done in my lifetime.

I've been having issues with that too!

[Marty Kasprzyk]

2 hours ago, Don Noon said:

> You might notice the lack of publications demonstrating effective use of modal information to make targeted changes to a response spectrum.

>

Maybe good makers got things to work really well and they want to keep things secret from their competitors.

[Don Noon]

25 minutes ago, Marty Kasprzyk said:

Maybe good makers got things to work really well and they want to keep things secret from their competitors.

Strad's "secret" has been kept so well that nobody has been able to discover it.  So they say.  And then there are some others who claim to have discovered Strad's secret.  But let's not travel that muddy road again.

[David Burgess]

1 hour ago, Marty Kasprzyk said:

Maybe good makers got things to work really well and they want to keep things secret from their competitors.

Quite plausible....
One can share quite a lot, without sharing the things they consider most valuable.

[Davide Sora]

1 hour ago, David Burgess said:

Quite plausible....
One can share quite a lot, without sharing the things they consider most valuable.

Or sharing so many things that the truly decisive ones are no longer distinguishable and go unnoticed.

[Dr. Mark]

--> "Or sharing so many things that the truly decisive ones are no longer distinguishable and go unnoticed." <--    lol true!  If we don't know what to look for, lots of things just pass us by.

 

[Don Noon]

Or the secrets one reputable maker shares is in direct opposition to another reputable maker's secrets.

[Davide Sora]

7 minutes ago, Don Noon said:

Or the secrets one reputable maker shares is in direct opposition to another reputable maker's secrets.

This happens often, it's the best tactic to confuse people and keep secrets. There is a secret agreement in this regard among reputable makers.

[Andreas Preuss]

7 hours ago, Marty Kasprzyk said:

Maybe good makers got things to work really well and they want to keep things secret from their competitors.

The thing is that secrets also serve as a kind of advertising even if there aren’t any.

Otherwise getting things working well is working consistently and with the willingness to sort out instruments which don’t reach certain self set standards. Eventually they can be altered later to match the self set standards or used for experimentation. 
 

If I would see a maker who tries to tell me that the sound of his/her instruments is based on one secret my answer is simply ‘ I am not interested, keep it for your happiness!’

[jezzupe]

1 hour ago, Andreas Preuss said:

The thing is that secrets also serve as a kind of advertising even if there aren’t any.

Otherwise getting things working well is working consistently and with the willingness to sort out instruments which don’t reach certain self set standards. Eventually they can be altered later to match the self set standards or used for experimentation. 
 

If I would see a maker who tries to tell me that the sound of his/her instruments is based on one secret my answer is simply ‘ I am not interested, keep it for your happiness!’

Well, I know your not interested, but, there is ONE secret, that like Davide says is very obvious so its not really a secret, but no one talks about it much...that is passion/love for building, to me it goes hand in hand with what I consider the most "scientific" and one and only other important thing...statistics

One who builds many instruments because that is what they love to do will find tonal success one way or another.

[LCF]

14 hours ago, Don Noon said:

It's one thing to know the mode shapes and frequencies, but another thing entirely to actually use that knowledge to adjust the sound.  I tried it a few times, trying to quiet down a mode around 1 kHz that was annoyingly loud.  I got the mode shape to change a bit, but it was still around the same frequency and loudness.  You might notice the lack of publications demonstrating effective use of modal information to make targeted changes to a response spectrum.

I have been taking response spectra of white bodies for a while (it's not that much extra work), and  I have seen wide variations that looked frighteningly different.  Fortunately I avoided the temptation to try to make it "better" at that stage, because after assembly, they all turned out similarly fine.

I have what I hope is a simple question. If you take a pair of magnets one inside the corpus and one outside with an aggregate mass of say 10g what happens to the disposition of the corpus modes as you move the weight around?   For example if you have an area of B1+ which is vibrating strongly how does that mode change if you put the weight at that spot? And what does it mean with respect to changes you could make by scraping there?

 

3 questions.

Nobody expects the Spanish inquisition. Bring me the comfey chaur. 

[Don Noon]

1 hour ago, LCF said:

I have what I hope is a simple question.

The question is relatively simple.  The answer, not so much.  And deciding ahead of time if a modification will make things better or worse... flip a coin.

I have done part of the experiment, tacking on 6.7g of clay at various spots on my testbed fiddle, and seeing what happens to the B1- and B1+ frequencies.  The change in B1- is the upper number of the pair.  You would think that adding mass to an active area would reduce the sound amplitude, which is most likely true for the low B modes.  However, if you work on an antinode that is the opposite sign of the predominant radiating antinodes, it should go the other way.

You should be able to push the B mode frequencies around in a semi-predictable manner like this.  Maybe you could tweak the amplitudes with further experience.  There are plenty of other modes that will be affected to some degree if you do anything, and good luck with all of that.  

The only attempt I might make at this kind of thing is to use a center-heavy bass bar to keep the B1+ frequency and amplitude down, or leaving some extra thickness under the bass F hole.  But I normally do that on the initial build.

[Andreas Preuss]

21 hours ago, Salve Håkedal said:

I have been tapping and recording frequencies for over 10 years (100+ instruments) in many stages; from wood billets to the set up instrument. I find it interesting. But how useful it has been is hard to say. What I do know, is that is has prevented me from developing badly funded and possibly harmful pet theories. And that's good!

Beware: I'm no scientist and my measuring methods/routines are sloppy.

Below is a plot of a hardangerfiddle. For "No neck" and "With pegs" I tapped where the left bridge foot will come. For "Fully set up" I tapped from the side to the top of the left bridge edge.

(Hardangerfiddles usually have thinner strings as well as somewhat thinner plates than most new violins. I don't think the added sympathetic strings takes the total string tension up to the tension of a normal violin string set.)

 I am not a scientist either. 
 

In general I think avoiding to fall in some traps is already a very good strategy. The more I got involved in trying to measure something I realized that too precise measurements are just giving details one doesn’t need to know and therefore can be confusing. Therefore I like also to look on low resolution graphs which seem to be much closer to the hearing impression. 
 

I quite don’t precisely understand what you mean ‘with pegs’. (With neck?) in the next step it is fully set up so you need the pegs to tune the instrument. 

[David Burgess]

12 hours ago, Davide Sora said:

This happens often, it's the best tactic to confuse people and keep secrets. There is a secret agreement in this regard among reputable makers.

Shh.

[LCF]

16 hours ago, Davide Sora said:

Or sharing so many things that the truly decisive ones are no longer distinguishable and go unnoticed.

I think that the best place to hide secrets is in plain sight. Nobody suspects that they're real or true then. 

In the areas of instrument making where I have good skills I have freely taught what I know but with human nature being what it is most people are driven to reinvent things for themselves. I think nobody learns much except by reinventing and internalising the things you teach them so it becomes their own experience. 

Tell people all you know, spill all the beans. They'll never be able to keep up!

[Salve Håkedal]

4 hours ago, Andreas Preuss said:

...

I quite don’t precisely understand what you mean ‘with pegs’. (With neck?) in the next step it is fully set up so you need the pegs to tune the instrument. 

There is 3 stages in the graph: first the unvarnished fiddle body alone, with the soundpost in place, then the varnished violin with neck and pegs and, of course, sound post in place, then the fully set up instrument.

(If you are interested in more stages, like fluting in only the back or top of the body without neck but sound post inserted, I have it. Or the change after the last stage: adding the sympathetic strings, I have that too. But as I state above: I can not really say that I have had much practical use for it.)