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Soundpost facts?


polkat
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With post fitting it is very important to factor out the variables. Personally I'd never move a post on a fiddle of value without reducing string tension. ......Reducing string tension and re applying it will have an effect on tone...this must be factored in to the general consideration.( over a day or so) That's why I I don't do last minute adjustments :)

Another very important thing to consider is tuning......Instruments generally sound far better when tuned correctly.............only ever evaluate an instrument when it is perfecly in tune.

Great advice!

Even if you don't reduce string tension, post adjustments take time to stabilize.

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Someone did write an article for one of the early music publications, and I believe there's also a webpage, promoting the idea that the ancients placed the bridge wherever they pleased. The evidence for that was old paintings. The only problem is that to swallow that theory, you have to ignore another gigantic body of more direct and contradictory evidence: marks on the tops of old instruments, which generally don't support that conclusion.

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When you are fitting up a new post, do you make a rough post and then move it around till you find the right place more or less and then finish the process. Or do you make a few soundposts to try different places? Moving it around, with the arch the way they are it would seem that you would need more than one post to find the best spot. But I don't have a lot of experience with it so I may be completely wrong on this. thanks. this tread has been very helpful.

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When moving the bridge is there not an effect of changing the position of the bridge relative to the soundpost and also changing the after length slightly as well? It seems to me that there are several important variables in play at the same time.

If I might chime in with limited knowledge but great interest. I own a number of violins that I have purchased on eBay and elsewhere. Mostly junky with a few exceptions. Some of these arrive without sound posts or with posts down. I've attached a photo of a very old violin. You will notice that the bridge feet marks are very high or north. These indentations appear to have been there for a very long time, with only light scuffing to the south. At first I set the violin up with the bridge in a normal position between the nicks and sound post set behind accordingly. This is not a great sounding violin with damages to the back, front and scroll. I paid about $60 for it. I thought if those bridge feet marks have been there for so long why not try the bridge there and bring the sound post up with it? Well, the result was a greatly improved sound. And, then I noticed it! The F holes are very low. The bridge was where it should be but the holes were much lower than normal. So, I suppose another factor is sound hole placement.

post-24794-1222370069_thumb.jpg

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I just move the bridge a little, ~1mm, this little amount of movement isn't a huge deal to the afterlength. Plus if you only move the e-string side of the bridge then you are only really affecting the afterlength of the e-string and to a lesser extent the a-string. The e-string's afterlength is "non-optimal" to begin with due to the fine tuner.

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The exact bridge placement is a very interesting subject. In some cases really tiny changes to the bridge's placement, can make a great difference on an instruments' sound, and there seems to be an optimum for every instrument. I do move the bridges around on instruments that have sound issues, but the movements seldom exceed 0,5 mm I think. Still, these tiny adjustments often make greater differences than most changes you can do to the post...

The idea I'm putting forth here is the idea that if the bridge is, say, 4mm off from it's theoretical "ideal" position, then, it really doesn't matter how much you attempt to find the correct sp position, you won't be able to until the bridge is where it is "supposed" to go.

I'll admit that I was on a bit of a fishing expedition here, attempting to find out how many makers use the suggestion by Sacconi that one can find the correct bridge line by making it occur exactly at the center of gravity of the top plate - before cutting the ff holes or inserting the bass bar.

if you consider that the neck has been put on straight and the end pin is centered, then the E/W position for the bridge is locked in by the top plate center line (it also helps if the bass bar falls where it is supposed to with regard to the bridge feet for this to work right), and then, if you ballance the top plate on a push pin along the center line, (for example) you can also lock in the correct N/S position for the bridge... (right?)

If you're very careful to measure correctly and inset the neck into the block to exactly the right depth, then the nut will wind up where it needs to be in order to have the correct string length & to have the bridge wind up where the ff hole nicks should go if they are to coincide with the line that was arrived at by using the center of gravity to locate it, rather than by relying on the string length or the ff hole positions alone.

This is somewhat an aesthetic property also, as the ff hole nick positions should probably end up somewhere close to being centered along the body of the ff hole rather than too far up or too far down along its length...

So, people who draw the ff holes according to some other method or plan may have to fudge somewhere in order to make it all "fit" the standard violin model. For example, they may have to alter the mass of the plate in order to shift the ballance point after the fact.

I guess my question is, is the Sacconi suggestion correct or incorrect?

If it is correct, then there is really only one exact correct position for the bridge, and further, one correct position for the sound post - give or take finding the exact "sweet" spot, or, that exact spot that works pragmatically which will always vary a tiny bit.

Am I way off here?

Does anyone have a method for testing the violin prior to setting it up, that will tell you if the bridge position is right according to the "marked" position, other than trial and error? (that is - centered between the ff holes, and aligned on the nicks)

Does this question need further clarification?

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CTviolin

I have always enjoyed your posts, but have little to contribute to your discussions.

I sense you are not fully back to MN, otherwise there would be 3 short post-hocs to the first post.

Opps, sorry - you are absolutely correct...

I also neglected any mention of beer, and did not use my trademarked "guffaw"!!

What was I thinking?

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& to have the bridge wind up where the ff hole nicks should go if they are to coincide with the line that was arrived at by using the center of gravity to locate it,

I guess my question is, is the Sacconi suggestion correct or incorrect?

My question is why should the center of gravity of the free top plate matter to anything. This will not be the center of gravity of the completed violin. In the end it is the completed violin that is of importance not the free top plate. Even neglecting that why should the center of gravity, the first moment, be of particular importance? Why not the second moment or the third? This discussion seems to have turned quite silly to me. Unless you can give a good reason for placing the bridge at the center of mass of a free top, not the whole violin or even the violin body, then it is stupid to say that it HAS to be there. Except because Saconni says that it has to be there based on nothing in particular?

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Pure sophist / ideal terms thought but.....The centre of gravity / balance of a cymbal might not be the best place to impact it for a big sound.........

Actually they are suspended from that point, not struck by that point! Cymbals are struck elsewhere.

The point is a top plate in a violin is not the same as the free top plate that you carve at your workbench. Once you glue it to the sides and back, and the neck too, it all vibrates as one whole unit of wood. You can't break it into the top vibrating in this way like a loudspeaker or the back vibrating like this... You really have to treat it all as a violin; not a top plate, a back plate, sides and a neck.

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My question is why should the center of gravity of the free top plate matter to anything. This will not be the center of gravity of the completed violin. In the end it is the completed violin that is of importance not the free top plate. Even neglecting that why should the center of gravity, the first moment, be of particular importance? Why not the second moment or the third? This discussion seems to have turned quite silly to me. Unless you can give a good reason for placing the bridge at the center of mass of a free top, not the whole violin or even the violin body, then it is stupid to say that it HAS to be there. Except because Saconni says that it has to be there based on nothing in particular?
This I think falls into the same category as theory of free plate tuning. Once fastened to the ribs, evrything goes out the window. Now, If plate tuning is undertaken on the assembled instrument and soundpost in place, there might be more meaningful results.
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This I think falls into the same category as theory of free plate tuning. Once fastened to the ribs, evrything goes out the window. Now, If plate tuning is undertaken on the assembled instrument and soundpost in place, there might be more meaningful results.

I suspect that this is what the sucessful builders who also study acoustics do! Based on their writtings, not personal communications.

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Yeah CT, who are you and what have you done with the real CT? :)

The Sacconi idea came up in this thread (link) with some interesting results, FWIW.

Otto Möckel present this idea of having the top balancing in the bridge line in his book "Die Kunst des Geigenbaues" from 1930. Maybe Sacconi got that idea from there?

Anders

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My question is why should the center of gravity of the free top plate matter to anything. This will not be the center of gravity of the completed violin. In the end it is the completed violin that is of importance not the free top plate. Even neglecting that why should the center of gravity, the first moment, be of particular importance? Why not the second moment or the third? This discussion seems to have turned quite silly to me. Unless you can give a good reason for placing the bridge at the center of mass of a free top, not the whole violin or even the violin body, then it is stupid to say that it HAS to be there. Except because Saconni says that it has to be there based on nothing in particular?

The idea of having the balance point in the bridge line probably is is more a guide to how to distribute the thicknesses in the plate rather than to play an important factor to the bridge. I think that following that rule will give plates that are slightly on the thick side below the bridge line. There is a possibility that the violins will sound stronger then. (I am not quite sure about that yet).

When it comes to plate tuning that also is a guide in the graduation process. It give a fairly precise information about the stiffness mass ratios. But I think the amplitudes of the tap tones are more important than the frequencies. The effective masses you get from a free plate should correlate with what you get in an assembled violin, more so for certain modes in the free plate than others.

By the way I tune backs with the ribs and neck - fingerbaord on. Then the modeds look more like they do in the finished violin. The mode 5 also looks similar in the top and back.

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Those seem to be from the rule of 5 and using 10/11 as the string length. If the overall length is 357.5 the string length is 10/11, 325. 3/5 of that is 195, leaving 2/5 of that 130 for the neck. You can also use the 1/11 32.5 as the rib height and bridge height if you go for ratios alll the way, and can get it to work. I think when the restorers or whoever "standardized" everything decided more instruments fell into that length and the ratios worked so they made it a rule. Instruments that didn't conform were made to conform.

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