How tight should a sound post be

[Dr. Mark]

1 hour ago, Michael Darnton said:

1 hour ago, Dr. Mark said:

God and the devil are in the details.

Or one's actual experience, perhaps.

It's certainly not my intent to knock experience and expertise, whether we're talking about violins or physical science.  Have I done so?

[Michael Darnton]

35 minutes ago, Dr. Mark said:

It's certainly not my intent to knock experience and expertise, whether we're talking about violins or physical science.  Have I done so?

Sometimes you appear to. I'm never quite sure.

[Dr. Mark]

59 minutes ago, Michael Darnton said:

Sometimes you appear to [knock experience and expertise]

I probably do appear to at times, but it's not that -.  For the record I consider your and the other experts' opinions expressed here as I do those of the professionals in my own or any other field.

By the way, regarding Gavin R's comments I found the following, which has a few somewhat inconclusive but interesting and possibly useful static stress maps (Figure 4 in the attached) with accompanying discussion.  Also other interesting data:

https://www.sciencedirect.com/science/article/pii/S1296207411000835

Any correct and sufficiently complete physical description of the instrument should be able to predict these results with reasonable accuracy.  I didn't see back or belly change in length reported on my first run-through, but maybe if I read it more carefully.  Mr. Zuger may also be interested in this - hope he's still around...

Just noticed Bruce Carlson is third author of the above.

[Michael Darnton]

Speaking observationally, not theoretically, tops do quite often shorten over time.

[Dr. Mark]

Yes, I was just pointing out that I didn't see that measurement reported in the paper.  Ah - maybe this: The violin as a structure–A consideration of the static force in the instrument, J. E. McLennan, CAS Newsletter, 34 (1980), pp. 15-19

On p. 18, Table 3 Displacements on Tensioning Strings of Violin up to Pitch indicates compression of the upper plate (Top Plate Length) but extension of the lower plate (Back Plate Length) as string tension is raised.

Yet Mr. Gavin says: " I am a physicist so my view of the mechanics would be that the tension on the strings will compress the body slightly along the length of the belly and back. This must happen due to the longitudinal curvature of belly and back".  Perhaps I'm driving the point too hard, but he's a physicist and seems to claim rather that compression must happen - how do we resolve this riddle?

[Michael Darnton]

We don't get bent out of shape about it unless you can suggest why it matters in some essential way to the violin makers who are reading this. If you can connect knowing this with some persistent violin making problem, I'm all ears, though.

Being right isn't nearly as valuable and interesting as being useful. IMO.

[Dr. Mark]

13 hours ago, Michael Darnton said:

Being right isn't nearly as valuable and interesting as being useful. IMO

lol dang.

(later) It's morning now.  It seems that what's useful is what we make use of, and along these lines we wouldn't want incorrect information being inadvertently used by ourselves or someone else.  A number of people with a theoretical and mathematical bent, and others with a more immediately practical interest who only want some conceptual understanding of how an instrument deforms, lurk on this website.  I suspect you're one of them.  Obviously, the indicated concept proposed by Gavin R appears to be wrong, and the question is whether he has supporting evidence.  By examining his other propositions we may be able to establish a reasonably complete and experimentally supported conceptual picture of the deformation of a violin under string tension, and all in one place.  It seems useful.

Being picky about such things is a character trait of mine, reinforced by my job requirements and my sadistic tendencies.  The latter statement is intended to be mildly humorous.

[Gavin R]

23 hours ago, Dr. Mark said:

That's not enough for admission to Clown College, although you may now go to a good restaurant in a bad suit and not get thrown out if you carry a photocopy of your GPA.  You still need: 

1. To illustrate your mastery of forming pre-conceived notions - to be evidenced through prior work, testimony, or practical examples which will be selected by the College.

2. Comparatively little experience with, or knowledge of, the subject matter of questions you choose to answer.  Note answers of sufficient detail will make you eligible for a bonus point towards your admission.

3. Unfamiliarity with prior research, including computer modelling and various failed alternative explanations

4. Proof of your ability to draw conclusions prior to carrying out experiments or to forego experimentation altogether.  Alternatively you may illustrate for the board a minimum level of experimental ineptness.

5. Evidence through written examination by the board that you thoroughly understand the following: asking any pertinent question is a sign of weakness and incompetence

If you can provide all of the above you will be eligible for an interview with the College and, if admitted, forfeit your right to be taken seriously.  I see that an essay follows your opening statement and perhaps here we'll learn more...

Good stuff. Very well written. 

[Gavin R]

Well anyway, I am going to experiment with sound post positioning and tuning the post to see what effect it has. Perhaps get a spectrum analyser on it. Yes I’m sure that’s been done a million times. I  haven’t read any of the scientific papers written on it but I may start doing that. I notice that some luthiers select and tune a post so that it has the same natural frequency as the top and back. This would presumably promote resonance at that particular frequency. I guess that’s generally only done for  good instruments.

[Gavin R]

11 hours ago, Dr. Mark said:

Yes, I was just pointing out that I didn't see that measurement reported in the paper.  Ah - maybe this: The violin as a structure–A consideration of the static force in the instrument, J. E. MacLennan, CAS Newsletter, 34 (1980), pp. 15-19

On p. 18, Table 3 Displacements on Tensioning Strings of Violin up to Pitch indicates compression of the upper plate (Top Plate Length) but extension of the lower plate (Back Plate Length) as string tension is raised.

Yet Mr. Gavin says: " I am a physicist so my view of the mechanics would be that the tension on the strings will compress the body slightly along the length of the belly and back. This must happen due to the longitudinal curvature of belly and back".  Perhaps I'm driving the point too hard, but he's a physicist and seems to claim rather that compression must happen - how do we resolve this riddle?

 

[Gavin R]

12 hours ago, Dr. Mark said:

I probably do appear to at times, but it's not that -.  For the record I consider your and the other experts' opinions expressed here as I do those of the professionals in my own or any other field.

By the way, regarding Gavin R's comments I found the following, which has a few somewhat inconclusive but interesting and possibly useful static stress maps (Figure 4 in the attached) with accompanying discussion.  Also other interesting data:

https://www.sciencedirect.com/science/article/pii/S1296207411000835

Any correct and sufficiently complete physical description of the instrument should be able to predict these results with reasonable accuracy.  I didn't see back or belly change in length reported on my first run-through, but maybe if I read it more carefully.  Mr. Zuger may also be interested in this - hope he's still around...

Just noticed Bruce Carlson is third author of the above.

Thanks. I will have a read of that. When moving a post I found that squeezing the sides loosened the post significantly. String tension did the same by compressing the body longitudinally. I am surprised the idea of an adjustable post hasn’t caught on given that such tiny changes make such a difference. An implement that holds the post firmly and allows easy repositioning must surely have also been invented. Would make trial and error positioning quicker compared with the traditional tool. 

[HoGo]

48 minutes ago, Gavin R said:

I am surprised the idea of an adjustable post hasn’t caught on given that such tiny changes make such a difference. An implement that holds the post firmly and allows easy repositioning must surely have also been invented. Would make trial and error positioning quicker compared with the traditional tool.

The adjustable posts are usually much heavier than simple spruce stick due to need of movable feet and some screw mechanism so they affect sound of violin in their own ways so are hardly comparable to traditional post. They are also quite expensive and you wouldn't want to install and adjust them on your own as they could easily lead to soundpost crack or other damage to violin.

If someone invented adjustable post that would weigh same as normal post then there's a chance it would stick with violin folks.

[Dr. Mark]

2 hours ago, Gavin R said:

Very well written

Thanks - my intent was, with a bit of humor, to express doubt and give you the opportunity to question your assumptions, but without putting you directly on the spot.  I picked up some of this method from reading John Baez' (at UC Riverside) stuff.  I do stuff like that and I blame it on my ptsd.  Related to your sound post interest, there is some prior work (that I'm not very familiar with) but that may be useful when designing your experiment; there's e.g. https://newt.phys.unsw.edu.au/music/people/mclennan_soundpost.html and his dissertation, neither of which I have (yet) read in any detail.  I'm also impressed with your measured response to my provocation - makes me think I could have used a better tone in my first response lol.

[Gavin R]

If there were an easier way I guess it would have been thought of by now. 

[Michael Darnton]

2 hours ago, Gavin R said:

An implement that holds the post firmly and allows easy repositioning must surely have also been invented. Would make trial and error positioning quicker compared with the traditional tool. 

You should be able to stuff the setter right back in to move the post around but most of us find that like with playing, practice makes moving posts around easy. Perhaps God made the job difficult specifically to discourage players and duffers from doing it?

It's a lot like writing for a child: impossible when you start; gets easy with practice.

I never understand why people complain about learning post setters when their whole life has been made of decades learning thousands of similarly difficult tasks. You'd think people would have learned the value of practice by now.

[Marty Kasprzyk]

2 hours ago, HoGo said:

The adjustable posts are usually much heavier than simple spruce stick due to need of movable feet and some screw mechanism so they affect sound of violin in their own ways so are hardly comparable to traditional post. They are also quite expensive and you wouldn't want to install and adjust them on your own as they could easily lead to soundpost crack or other damage to violin.

If someone invented adjustable post that would weigh same as normal post then there's a chance it would stick with violin folks.

Since one function of the sound post is to prevent the top plate from moving at the soundpost location I  anticipate that a heavy soundpost would work better than a light one.  On the other hand, since the back plate is much heavier a sound post a few grams heavier probably wouldn't have much effect.

I also guess that spruce was originally used because scrap pieces left over from making the blocks and top plates were laying around.  It easily splits so it was used rather than the heavier curly maple scraps.

Since these first spruce soundposts worked well there was never any incentive to find anything better.

 

[VicM]

24 minutes ago, Marty Kasprzyk said:

Since one function of the sound post is to prevent the top plate from moving at the soundpost location I  anticipate

The soundpost does NOT prevent the top plate from moving at the soundpost location. I wonder if you have ever payed any attention to anything....

[VicM]

4 hours ago, Gavin R said:

Well anyway, I am going to experiment with sound post positioning and tuning the post to see what effect it has. Perhaps get a spectrum analyser on it. Yes I’m sure that’s been done a million times. I  haven’t read any of the scientific papers written on it but I may start doing that. I notice that some luthiers select and tune a post so that it has the same natural frequency as the top and back. This would presumably promote resonance at that particular frequency. I guess that’s generally only done for  good instruments.

You can not experiment with sound post positioning because any change in position affects the fit and fit is 99% of the working goodness of the soundpost. Getting a spectrum analyzer on it hasn't been done a million times and it's not going to be a useful expenditure of time. You can not tune a soundpost  so that "so that it has the same natural frequency as the top and back". There isn't enough material or geometry to achieve that.

[Marty Kasprzyk]

25 minutes ago, VicM said:

The soundpost does NOT prevent the top plate from moving at the soundpost location. I wonder if you have ever payed any attention to anything....

You're right.  The soundpost does not prevent the top plate from moving at the soundpost position.  I should have said:

"Since one functrion of the soundpost is to greatly reduce the top plate from moving at the soundpost location,"

[Chris Anderson, PhD]

After reading several books, skulking on this forum for quite some time, I've come to a few simple adjustment conclusions. 

Assumptions: Bridge has already been expertly placed between the f-holes at the appropriate position, feet shaped to maximize transfer of vibration, bridge carved.

1. Sound post moved closer to F-hole increases stiffness and volume in high strings. Moving too close to F-hole will cause high strings to be 'too loud' relative to other strings.  it also increases overall stress in the plates, increasing tension of top and bottom (akin to putting a stick in the jaws of a crocodile - it should only go in so far, before either the croc- or the stick- breaks...)  The remaining items regarding 'tone' are resulting from this post 'tightness'.  

2. Sound post moved away from the f-hole (toward the bass bar) gives a richer, deeper tone - but the volume of the lower strings can go out of balance as compared to the rest of the strings.  This adjustment might require a replacement if the post 'falls over' due to looseness. 

3. Sound post moved closer to bridge (optimum position being 3mm edge-to-edge toward end-pin) will NORMALLY maximize volume, and also makes the sound 'brighter'. 

4. Sound post moved away from the bridge (to a point, 3.5 or 4mm? max), will give a 'warmer' tone at the sacrifice of some volume.  When working with kids (new learners), this is an acceptable sacrifice - as an improved tone can make them 'want to play more'.  Most new learners have unpracticed bow technique which causes a scratchy and brighter tone. However, this intentional 'handicap' can become more of a detriment for soloists, who need the additional expression and volume that comes from an optimally placed soundpost. 

5. Moving the sound post too far away from the bridge toward the endpin will dull the sound.  Tone becomes flatter and volume is even more reduced. (somewhat akin to playing with a 'fallen' sound post). 

6. Moving the sound post < 2mm or 'directly under' the foot of the bridge can maximize brightness, and I don't know what happens when its moved 'beyond' the bridge (my feeling is that's out-of-the-question. )

7. Thicker diameter of post makes sound 'darker'.  Too thick makes it 'dull'.  Thinner makes for 'brighter' and 'too thin' can should shrill.  

Reading through Gavin R's physics assessment was edifying.  I very much appreciated the acoustical discussion from a rumination standpoint, but in this case, the position of the soundpost relative to the bridge foot is of far more importance than its overall 'tension'.  If any of these statements are incorrect - I will be happy to make corrections.  

thanks, 

Chris Anderson 

Sources: 

Some of my comments on lateral movement came from a book (and I can't remember which one).  Other considerations are by luthiers below: 

 

 

[martin swan]

I wonder if it makes that much sense to think about the soundpost in terms of "function".

[Victor Roman]

45 minutes ago, Chris Anderson, PhD said:

4. Sound post moved away from the bridge (to a point, 3.5 or 4mm? max), will give a 'warmer' tone at the sacrifice of some volume. 

This is something one of the TOP people here might want to comment on. Soundpost far from the bridge ( 4-5mm ) was common when I was young at least within my geographical area. I thought it made the violin more.....pliable, somehow more forgiving, more flexible, at the cost of the A string becoming somehow "erratic". I received a very thorough "paper" on soundpost function and adjustment from a member here and from what I could grasp ( still trying to get my head around it ) any N-S move of the post needs to be compensated by an E-W one in order to maintain a certain balance and avoid volume gaps throughout the diapason. These are a big problem as the player does not hear them. Until I had my ( German ) violin properly adjusted I simply played louder in certain registers and softer in others based on what competent listeners noticed. That was a chore as it was related to the actual string. And in a "busy" quartet there are a lot of other things to keep an ear on.

[Mark Norfleet]

55 minutes ago, martin swan said:

I wonder if it makes that much sense to think about the soundpost in terms of "function".

As do I.

Conventional wisdom, such as offered by @Chris Anderson, PhD, has it's limits.

 

[Victor Roman]

1 hour ago, martin swan said:

I wonder if it makes that much sense to think about the soundpost in terms of "function".

Am curious as to what you mean. Take the soundpost out of a violin and then use it to play the 1st in a fairly busy quartet. It won't work. That means to me, it does have at least one function. 

[martin swan]

1 minute ago, Mark Norfleet said:

As do I.

Conventional wisdom, such as offered by @Chris Anderson, PhD, has it's limits.

 

I mean was the soundpost invented in order to perform a function, or is it a feature which evolved/was inherited from other instruments or objects and which happens to have effects (many of which resist all attempts at systematization).

I would speculate that the soundpost was initially simply a brace ie. to prevent thinner and therefore more resonant and musically appealing plates from breaking or collapsing.