Shim under bone saddle: defeats the purpose?

[drive-south]

Originally Posted by steveyam

It's all down to the shim material. If the shim has tonal sapping qualities eg a piece of soft wood, then yes it will degrade the sound. Using a tonewood shim such as ebony or maple will be fine because it won't compress any more than the parent bridge material; vibrations will be transmitted just fine. In some of my guitars I have two shims and I don't believe it is affecting my tone one tenth as much as the lack of practise that I put in. And I don't practise..

I think you are forgetting that no piece of material will ever be perfectly flat. So you have multiple surfaces that are contacting each other, and neither piece is perfectly flat so there are voids between the 2 surfaces. So there are voids between the saddle and the top of the shim, and voids between the bottom of the shim and the top of the bridge slot. Those voids add up. If there are 2 layers of shim, there are voids between each layer. In my opinion, this is a situation we all should avoid.

Consider the irony of paying in excess of $100 for a FWI saddle blank, then ending up with shims under it. It does defeat the purpose of carefully selecting material, making sure the saddle is properly shaped. Any shim is a red herring that really doesn't belong there.

[rick-slo]

Originally Posted by drive-south

I think you are forgetting that no piece of material will ever be perfectly flat. So you have multiple surfaces that are contacting each other, and neither piece is perfectly flat so there are voids between the 2 surfaces. So there are voids between the saddle and the top of the shim, and voids between the bottom of the shim and the top of the bridge slot. Those voids add up. If there are 2 layers of shim, there are voids between each layer. In my opinion, this is a situation we all should avoid.

Consider the irony of paying in excess of $100 for a FWI saddle blank, then ending up with shims under it. It does defeat the purpose of carefully selecting material, making sure the saddle is properly shaped. Any shim is a red herring that really doesn't belong there.

The key in sound for the different saddle materials is at the string/saddle point of contact.

[Alan Carruth]

steveyam:
I haven't had a chance to do any testing with the Bridge Doctor, so I can't to say much about how it works. These things get complicated...

SteveS wrote:

"If the vertical movement of the bridge was the essential factor, then the height of the bridge would have little impact on the output of the guitar. If a rocking of the bridge was the major contributor to volume, then the bridge height would play a major roll in volume. The fit of the bridge would also be important because a lose bridge would not transmit rocking motion. Because these two cases are true, it seems evident that the motion on the bridge is primarily rocking, not up and down."

Like I said above, these things get complicated...

Part of the problem here is that out ears are not really very sensitive to fairly large changes in power if the spectrum stays the same: that 20 dB stronger signal I talked about really 'sounds' about four times as loud, even though it's got a hundred times as much power. The 'transverse' force signal averages about seven times as powerful as the tension change signal, but that's only about 7dB: try boosting your sound system by that much some time, and see how much louder it sounds.

In an experiment that I'm currently writing up, I investigated string height off the top as a variable in tone production. Sure enough, raising the strings off the top does make an audible diference in the sound, and the biggest contribution to that seems to be from the tension signal, since analysis of the spectra of the strings showed more output in the even-order partials that the tension change signal produces. BUT, most of the power was still being produced by the transverse force signal, pushing the top in and out like a loudspeaker: the overall power was nearly the same (and possibly even less with the taller saddle), but the overtone 'recipe' was different.

The thing here is that people were able to hear a 'change', but that's what your senses are built to detect. Stuff that stays the same doesn't grab your attention, but you're pretty sensitive to small changes (the little noise the tiger makes in the bush...)

Remember, too, that doing things that change the bridge-rocking signal, like raising the saddle or installing a Bridge Doctor, also change the stresses on the top, and alter the way it vibrates. That, in itself, can make a big difference in the sound.

In the end, science is about winnowing things out, and figuring out what's more or less likely. You can't 'prove' anything happens, but you can show that something is more or less likely. I can't tell you that bridge rocking is not important; in fact, I know that it does contribute to the sound, at least in terms of 'timbre'. What I can say, though, is that all of the evidence I've got, and all of the research I've seen, says that the transverse force has the most energy to contribute, and the most effective path for doing it. Based on that, I'm not going to _ignore_ the tension change signal, but I'm not going to spend a lot of effort to enhance that mode of top driving, particularly if it seems to conflict with the effective 'loudspeaker' motion of the top driven by the transverse force.

One final question for you:
On guitars with tailpieces (or violins) the strings can't drive the top very effectively through the 'bridge rocking' mechanism (and yes, I've measured that). The tension change signal is frequency-doubled with respect to the fundamental of the string: if the low A is tuned to 110 Hz, the tension change signal only contains frequencies that are even multiples of that (220, 440, 660, and so on). Thus, if a flat-top is primarily driven by the tension change signal, it ought to be sounding those frequencies. Why, then, do archtop guitars, which _must_ be driven overwhelmingly by the transverse signal, not sound an octave below flat tops with the same strings?

[Dogberry415]

As the author of the original post of this thread, I'm amazed at what I've started. I've learned a great deal about guitars in this forum, but I can't remember learning so much in one thread. I'm really grateful to be able to access the wealth of knowledge that everyone shares so willingly. To all who have weighed in on this subject (and who are still weighing in as I type), I just wanted to say thanks. This is an amazing place for a guitar player to be.

[Taildragger]

Originally Posted by Dogberry415

As the author of the original post of this thread, I'm amazed at what I've started. I've learned a great deal about guitars in this forum, but I can't remember learning so much in one thread. I'm really grateful to be able to access the wealth of knowledge that everyone shares so willingly. To all who have weighed in on this subject (and who are still weighing in as I type), I just wanted to say thanks. This is an amazing place for a guitar player to be.

OK Dogberry415, I'll bite. What did you learn? Shim, or no shim?

It has been an interesting thread to watch. I thought for sure we were going to finally find out which is better - Taylor or Martin

-mike

[SteveS]

Alan,
Thank you again for your response! Would be a bit of an understatement to say that final agreement on how sound is generated and how best to make a top is a distance of?

Originally Posted by Alan Carruth

......One final question for you:
On guitars with tailpieces (or violins) the strings can't drive the top very effectively through the 'bridge rocking' mechanism (and yes, I've measured that). The tension change signal is frequency-doubled with respect to the fundamental of the string: if the low A is tuned to 110 Hz, the tension change signal only contains frequencies that are even multiples of that (220, 440, 660, and so on). Thus, if a flat-top is primarily driven by the tension change signal, it ought to be sounding those frequencies. Why, then, do archtop guitars, which _must_ be driven overwhelmingly by the transverse signal, not sound an octave below flat tops with the same strings?

Easy - Because it is not in their nature.
(Yes - I know, true but a really smarty pants answer.)

Certainly, archtop guitars are primarily driven by transverse motion. The thought of a rocking or even forward/backward drive being fundamental is nonsensical with a tail piece and non-fixed bridge. Clearly, the primary, if not the only drive for these instruments is transverse.

I do not make archtop guitars. I have not played one that I appreciated the sound. They strike me as thin sounding - not good bass response. I do not claim to have much knowledge or any experience with these instruments through playing or building. I do love their looks.

String attachment is not the only difference - ladder bracing instead of X bracing stands out as a very significant feature which I believe would cut lower frequencies by blocking monopole movement.. While I do not know the answer, I suspect that the ladder bracing is the primary reason that lows are not very good on archtops. The other reason is that this type of string attachment does not transmit energy to the top with near the efficiency of the flat top design. The energy to drive bass is just not available in an archtop.

So, how’s that for a guess?

[darylcrisp]

for myself, i've used ebony shims and rosewood shims(to match the bridge wood), and a time or two simply used properly cut paper shims. after a "correctly" cut saddle was remade and installed, i nor the person owning the guitar could tell any differences-all instances.

there's so many other things going on in the lower bout, a shim properly placed under a saddle, just doesn't bother me.

good post, excellent replies and thoughts
d

[Dogberry415]

Originally Posted by Taildragger

OK Dogberry415, I'll bite. What did you learn? Shim, or no shim?
-mike

Well, now that the dust has settled, the take-away I'm getting is this:

There probably isn't enough of a difference between shim vs. no shim to really call it an issue, in terms of tone and volume... especially if the shim and the bridge are made of the same tonewood. However, no one has refuted the obvious idea that best-case scenario is to have no extra layer of anything between the saddle and the bridge.

Let's see if 18 people now scuffle over what I've learned.

[charles Tauber]

Originally Posted by SteveS

archtop guitars... They strike me as thin sounding - not good bass response. I do not claim to have much knowledge or any experience with these instruments through playing or building. I do love their looks.

Respectfully, try this for bass response - one of my 7-string archtops played by Michael Maguire: http://www.myspace.com/michaelmaguiremusic/music

I suspect that the ladder bracing is the primary reason that lows are not very good on archtops.

Archtops are traditionally braced with an X or an A, rather than ladder, with no back braces.

[El Conquistador]

Originally Posted by SteveS

I have not played one that I appreciated the sound. They strike me as thin sounding - not good bass response.

This has been my experience as well. While I love the look, I just have not found tonal satisfaction in any archtop I have played.

However, Charles, your clip certainly does sound wonderful. Makes me wonder why I have not run into one that does it for me?

Steve

[steveyam]

Originally Posted by drive-south

I think you are forgetting that no piece of material will ever be perfectly flat. So you have multiple surfaces that are contacting each other, and neither piece is perfectly flat so there are voids between the 2 surfaces. So there are voids between the saddle and the top of the shim, and voids between the bottom of the shim and the top of the bridge slot. Those voids add up. If there are 2 layers of shim, there are voids between each layer. In my opinion, this is a situation we all should avoid.

Consider the irony of paying in excess of $100 for a FWI saddle blank, then ending up with shims under it. It does defeat the purpose of carefully selecting material, making sure the saddle is properly shaped. Any shim is a red herring that really doesn't belong there.

Of course I am aware of the voids issue. I make sure my saddles and shims are perfectly flat using a rigid, surface ground Stewmac fretboard leveller with fine sandpaper on it to perform final levelling. There's no voids. Frankly, two shims isn't my first choice, but in practise it's not a problem. There's never going to be an 'answer' to this thread because people are polarised about it, and sadly, often with no real knowledge or experience, just anecdotal theories. I say, use sound engineering practise; flat surfaces, right angled corners etc etc and you can do lots of stuff! So, the answer is easy; if using shims bothers you, then dont. If using shims is ok by you, then do. That's it. That's the answer. Do what makes you feel good, cos you won't hear the difference if the job is done correctly. Trust me, I'm a doctor.

[Ivan Lee]

Such a timely thread.......

Just had a tech take my FWI bridge down too far!!!

Trying to decide now between getting a new blank and making my own or shimming........

[steveyam]

Originally Posted by Ivan Lee

Such a timely thread.......

Just had a tech take my FWI bridge down too far!!!

Trying to decide now between getting a new blank and making my own or shimming........

Contact hobbies veneers companies, and ask them for their sample packs. Mine have lasted me a lifetime.

[Tony Burns]

Make a new saddle -their not hard to do , and the solidness of a one piece bone saddle sounds better. It makes a good guitar great. Dont be a cheap skate on this it does make a difference !

[steveyam]

Originally Posted by Tony Burns

Make a new saddle -their not hard to do , and the solidness of a one piece bone saddle sounds better. It makes a good guitar great. Dont be a cheap skate on this it does make a difference !

Oh right, thanks for that. Some of the best brains on the forum have just spent 3 pages debating in. Now we know definitively..