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soundpost diameter and sound


actonern
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I'm interested in learning more about the effect of sound post mass and its influence on shaping an instruments sound.

Have any of you experimented with different sound post diameters and if so, are there any general tendencies that emerge?

For instance, would a violin that tends to shrillness benefit from a heavier post or is the opposite true?

Best regards,

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I think that the position and "pressure" of the post are more important than the material or small differences in diameter. But if you think the material is important, try a thicker post made of soft spruce.

You may try also fitting the post with less pressure and a bit more behind the bridge to cure the shrillness. Moving the tailpiece up a bit may also be tried, as well as trying different strings.

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Excellent advice from Manfio, as usual. I was involved in soundpost trials where only the diameter of the post was reduced (a tricky experiment) It seems that a post acts somewhat as a filter . A thinner post will increase sound production while a thicker one has some damping effect. So a good sounding instrument can benefit from a thinner post while an instrument with acoustical problems will benefit from a thicker post.

Oded

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Excellent advice from Manfio, as usual. I was involved in soundpost trials where only the diameter of the post was reduced (a tricky experiment) It seems that a post acts somewhat as a filter . A thinner post will increase sound production while a thicker one has some damping effect. So a good sounding instrument can benefit from a thinner post while an instrument with acoustical problems will benefit from a thicker post.

Oded

Hmmm.... Oded, I'll have to think about that and compare it to my own experiences, notes and memory... but the conclusion is not "ringing true" for me (sorry about the pun) as I read this. Maybe a case of limited sample size?

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Hi Jefferey,

The experiment was specifically aimed at a narrow question of soundpost thickness. We tested three very different violins beginning with extra thick soundposts (~6.5mm) and gradually reducing the thickness of each post. IIRC we had 4-5 listeners and did some blind listening tests. These tests took place over about a week's time.

The question of sounposts with different densities is a completely different issue about which I have some experience on cellos but not much with violins (except anecdotal)

Interested in your observations on this Jefferey.

Oded

PS in the original question the issue is posed as a question of 'mass' which perhaps the questioner confuses with density. Thinning a soundpost will reduce it's mass but not it's density.

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"PS in the original question the issue is posed as a question of 'mass' which perhaps the questioner confuses with density. Thinning a soundpost will reduce it's mass but not it's density."

Oded, you're right... I clumsily assumed that the density of the posts for this purpose was close to identical and that the diameter would control the mass...

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The experiment was specifically aimed at a narrow question of soundpost thickness. We tested three very different violins beginning with extra thick soundposts (~6.5mm) and gradually reducing the thickness of each post. IIRC we had 4-5 listeners and did some blind listening tests. These tests took place over about a week's time.

Hi Oded;

It will probably be several days before I have the time to devote much brainpower to this... kinda' occupied... but I wonder if your experiment was limited by sample size (the instruments you tried this with; the post density chosen), as again... the conclusion does not seem to be agreeing with my experiences... As a matter of fact, it's not unusual for me to settle on posts 6.2 and larger (6.5) for the better (quality and sound) instruments I'm working with (for better players). Some factors that I've mentally noted, that I believe have bearing on the post diameter I settle on, include materials (in the violin), arching, plate thicknesses (stiffness), and the rest of the setup... but this is a knee jerk reaction to your findings so take it with a grain of salt.

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Any difference in tone between a thick post and a thin one has nothing to do with mass, at least according to my experiments. Some time ago, I took small brass square wire with double sided tape on it, and fashioned a tool to attach the weight on the post, thus affecting post mass without adjusting other variables.

Even when the configuration was equivalent to more than doubling the post mass (a good order magnitude greater change than can be affected by different sound post diameters) the change in tone was negligable, at least at that time. My conclusion was that variation in tone from post diameter changes were due to other things like total area of surface contact at the top and bottom. However, I have not repeated the experiment in some time, and reserve the right to be wrong in the event my listening ability has improved since then.

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While we felt very comfortable with our basic conclusion about the consequences of a thinner soundpost some of the implications aren't so straight forward.

For instance, since a thicker soundpost will smooth out the sound, strong players often will prefer this because it means they can more comfortably bear down on the strings. There is also an element of bow feel which we didn't get into but which I suspect favors the thicker soundpost.

As I said our experiment was narrowly defined: given the same player and listeners on three very different instruments, changing only post diameter but not location or tension, what is the result.

Oded

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Any difference in tone between a thick post and a thin one has nothing to do with mass, at least according to my experiments. Some time ago, I took small brass square wire with double sided tape on it, and fashioned a tool to attach the weight on the post, thus affecting post mass without adjusting other variables.

Even when the configuration was equivalent to more than doubling the post mass (a good order magnitude greater change than can be affected by different sound post diameters) the change in tone was negligable, at least at that time. My conclusion was that variation in tone from post diameter changes were due to other things like total area of surface contact at the top and bottom. However, I have not repeated the experiment in some time, and reserve the right to be wrong in the event my listening ability has improved since then.

I find your experiment with adding mass very interesting, and according to your results it doesn't look like the mass is very critical. I admire the fact that you took the time to verify if this is indeed something worth consideration.

This brings up a personal observation: I notice people often get hung up on very minor or or almost non-existent parameters concerning the violin. If parameters such as the mass of the post produce inconclusive results, why bother messing around with something that appears to be very low on the totem pole of difference? This is akin to experimenting with different densities of purfling in the quest for the "ultimate sound". In my opinion time is better spent learning to evaluate and understand the things that make major affects on sound, and the little things will look after themselves as you work from the top of the totem pole downwards.

The surface contact area of the post is interesting though. I wonder what affect a post shaped something like a double headed golf tee would sound like?

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"I wonder what affect a post shaped something like a double headed golf tee would sound like?"

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At that time, I also conducted an interesting destructive test. I took a violin with a snug post, observed the tone, and then used a saw through the f hole to carefully cut two notches (about a third or halfway) through the post while in place, effectively changing the structural integrity of the post without altering position.

The change in tone was quite detrimental. If I had to apply this information to a golf tee post, my guess is that there would be a loss of sound quality. Increased soundpost stability seems to be a desirable characteristic.

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"I wonder what affect a post shaped something like a double headed golf tee would sound like?"

-----------------------------------------------------------------------------------------------------------------

At that time, I also conducted an interesting destructive test. I took a violin with a snug post, observed the tone, and then used a saw through the f hole to carefully cut two notches (about a third or halfway) through the post while in place, effectively changing the structural integrity of the post without altering position.

The change in tone was quite detrimental.

It would appear that a uniform, round post is still the best for our purposes, diameter changing slightly to suit the particular instrument.

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Any difference in tone between a thick post and a thin one has nothing to do with mass, at least according to my experiments. Some time ago, I took small brass square wire with double sided tape on it, and fashioned a tool to attach the weight on the post, thus affecting post mass without adjusting other variables.

My concern with this experiment is that the wire might not have been attached firmly enough to the post, the tape probably had a good amount of "give" in it and this could affect the results. The results would be more convincing if the wire had been glued rigidly to the post. Another alternative is to attach a mass outside of the violin at the post position but this isn't quite the same as adding mass to the post itself.

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My concern with this experiment is that the wire might not have been attached firmly enough to the post, the tape probably had a good amount of "give" in it and this could affect the results. The results would be more convincing if the wire had been glued rigidly to the post. Another alternative is to attach a mass outside of the violin at the post position but this isn't quite the same as adding mass to the post itself.

Speaking as one who is learning about all this stuff I want to ask a couple of questions. I think of the sound post as being the connection between the top plate and the back, transmitting the vibrations of the strings from the top to the back. So it would seem that a larger post diameter would, up to a point, be better for the connection between the top and the back. If the post is too thin, and thus too flexible, it might tend to absorb and damp rather than transmit vibrations. Does this make sense?

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Speaking as one who is learning about all this stuff I want to ask a couple of questions. I think of the sound post as being the connection between the top plate and the back, transmitting the vibrations of the strings from the top to the back. So it would seem that a larger post diameter would, up to a point, be better for the connection between the top and the back. If the post is too thin, and thus too flexible, it might tend to absorb and damp rather than transmit vibrations. Does this make sense?

Keep in mind it takes more energy input to move a larger mass. To drive maximum energy into the back plate an ideal post would probably be extremely light, but very dense while maintaining the surface area contact on the plates. Of course this material doesn't exist, but maximum obtainable density to weight ratio is probably pretty close to what spruce or pine is.

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Speaking as one who is learning about all this stuff I want to ask a couple of questions. I think of the sound post as being the connection between the top plate and the back, transmitting the vibrations of the strings from the top to the back. So it would seem that a larger post diameter would, up to a point, be better for the connection between the top and the back. If the post is too thin, and thus too flexible, it might tend to absorb and damp rather than transmit vibrations. Does this make sense?

No the post is not there to transmit vibrations. Guitars don't have posts but yet their backs vibrate quite a bit! Some people have said that the post's role is to define a node (a point of zero vibration) at the e-string bridge foot, this is true at some frequencies but not true at others.

I think that one important thing that the post does is that it makes the e-string bridge foot "feel" a higher stiffness than the g-string bridge foot (though I suspect that a violin with the bass bar under the e-string foot and a -post under the g-string foot would work just as well). This results in the violin vibrating in a manner which is more likely to project sound well, as compared to say guitars which project relatively poorly.

There are a lot of things that the soundpost might be doing in a violin. Some of these are related to simple properties such as the mass, density, and stiffness of the post (or you can lump all this stuff together into an impedance). This is what people have focused on up until now.

I have some ideas that I have been thinking on which relate to other things the post may be doing in a violin. These relate to why the fit of the post is important and so are directly related to things applicable to a violinmaker. I'm not going to say more on this until I set up experiments, do some proper calculations, and reach conclusions. Don't hold your breath, this will take a while because I would like the results might be good enough for some type of publication. The same thing goes for my violin f-hole experiments, I'm not giving out details on that project because I have no conclusions yet and I want to turn the project into something more than just graphs on my harddrive.

I think the full role of the soundpost is only partly understood at the moment.

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Any difference in tone between a thick post and a thin one has nothing to do with mass, at least according to my experiments. Some time ago, I took small brass square wire with double sided tape on it, and fashioned a tool to attach the weight on the post, thus affecting post mass without adjusting other variables.

Now that I think about this more it might be wrong to assume that a lump of mass concentrated at one part of the post is the same as a post that is heavier but with the mass distributed uniformly along its length. Lumping the mass at one point is going to cause the impedance of the post to vary strongly along its length so by attaching a mass to your post you did affect other variables. A normal post would however have a uniform impedance along its length, if it has a constant density and crossectional area. How important is the impedance of the post to violin tone? I don't remember that, I've read a paper on it but I don't remember the conclusions. The paper was by a researcher in the Australian musical instrument acoustics group.

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"My concern with this experiment is that the wire might not have been attached firmly enough to the post, the tape probably had a good amount of "give" in it and this could affect the results. The results would be more convincing if the wire had been glued rigidly to the post. Another alternative is to attach a mass outside of the violin at the post position but this isn't quite the same as adding mass to the post itself."

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There is validity to your observation, but the DS tape ran the length of the brass flat, making for a respectable coupling, and even if the net effect was equivalent to a very conservative 10% of the potential damping from additional mass that might be encountered with gluing, a negligable result would still support the conclusion. The DS tape I used is very thin at about .002", and I would say it has give, but not a good amount in the overall context of the experiment. However, perhaps some ambitious luthier will replicate the experiment with glue. Any volunteers, Mr. Johnson? :)

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"Now that I think about this more it might be wrong to assume that a lump of mass concentrated at one part of the post is the same as a post that is heavier but with the mass distributed uniformly along its length."

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Indeed, it is not the same, but using such a dramatically different mass than might be encountered with post diameter changes should have resulted in much more obvious changes.

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"But this Mr. Johnston has his own soundpost experiments which could answer much more interesting, in my opinion, questions relating to soundpost fitting."

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Hmm... anything you can share, Mr. Jonston? :)

Anything I say now would be speculation. I'm waiting until I have results, either null or confirmation is fine with me. I want to be able to say, this is something the post can do, here was my experiment, the result is it's an important or not important effect. Until I can do that I'm keeping quiet on the details.

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