Tap Tuning Question

Violent5

Violent5

New member
For you guitar builders is tap tuning an essential part of a build? Or is it bs? Anyone have experience tap tuning plates? Do you have any quick advice on the subject?

I briefly experimented taping the braces of a back and top plate. Most of the taps on most of the braces would produce a ringing tone that sounded like the same pitch of the other braces on the same plate. I didn't use a tuner to try to actually tune the braces because they ring so well I was scared to alter them anyway. I just went ahead and glued the top, sides and back without tap tuning. This is my first build so I thought I'd ask for next time.


Thanks
 
Nope, don't do it. Not even when I'm making acoustics. The basic premise of tap tuning is to make your guitars more consistent, but as near as I can tell the builders who do it have the same level of variability as those of us who don't. And the most consistent guitars I know of (even if I don't like them) are Taylor guitars, and if you think Bob Taylor is going to waste his time on tap tuning, you are kidding yourself. Bob's goal is to get every guitar in and out of the factory with less than 15 hours of labor. Tap tuning isn't part of that equation!

Muttley will probably come along and disagree with me soon, as I believe he is one of those tap tuning guys.


Light

"Cowards can never be moral."
M.K. Gandhi
 
First, I don't tap tune but I do have a lot and I mean a lot, of research experience in the subject. So here goes..

Tap tuning in it's original form came about as a method of attempting to replicate the violin tops and backs of the early masters. In the guitar world it was adopted by Smirnoff et al as a method of building consistent instruments and many interesting studies have been done following papers published by Carleen Huthins of the Catgut musical acoustic society and Joseph Curtin who extended the practice in a few ways.

Essentially tap tuning involves getting the fundamental ring tone or tap tone of the back and front to a specific pitch. In your example you will only have a single pitch because that is the fundamental mode of vibration of that piece. It is often called the ring tone because the vibration of the top would resemble a ring around the body where you have a node or point of no vibration. For an explanation of that google Chladni plates. The top also has other modes of vibration which would as expected fall around the normal harmonic series and when examined they form other node shapes on the top.

Now the pitch at which the fundamental mode of vibration occurs can be altered by using our old friend mass/stiffness ratio. The frequency is mainly dependant on the overall mass and stiffness of the materials which for a given unit volume is constant. You can't change the stiffness but you can change the mass by thicknessing the plate or adding and shaving braces. Doing so will change the fundamental pitch and also the frequency of the other modes and it is that that people are tinkering with when they "tap tune"
plates.

So what supposed benefits and how much is of little consequence? First there are as many theories as there are makers so having dealt with the physics which can't be denied, onto the most common reasons and opinions. Most attempt to get the frequency of the top and the back plates tuned so they don't fall right on a frequency that is used in our A440 harmonic scale and also tune the top and the back about a half tone apart. They postulate that the presence of weak and or strong wolf tones in the instrument are a result of the ring tone being more easily excited than others and that tuning them apart helps stop the plates driving each other at at a specific frequency. There may be some mileage in this theory for bowed instruments where a constant supply of energy is being put into the string and hence the top. Not so much for plucked instruments in my opinion.

The flaw in this theory and a flaw in the all theories on tap tuning in isolation is that the moment you glue the top and back onto the ribs you once again change the way the top and back vibrate by adding a clamping point to the edge in physics terms it is no longer a free plate but more a membrane and you alter the frequency once again. Adding bindings or purfling changes this again and strangely the plate starts to behave as what physics would describe as a beam in some regards.You also bring into play a whole new set of acoustic considerations in particular the body chambre which has it's own set of modes of vibration just like the back and the top. These also influence the sound of the finished instrument.

There has been some decent research recently on attempting to predict the modes on plates that are on the instrument. Right now I don't have the reference but I'll try and remember to dig it out. It's merit is still dubious because as you can see we are dealing with a very complex model and predicting let alone controlling changes and effects on tone using these methods is an absolute mine field, and I haven't even touched on many other critical factors such as Q factor which is essentially impedance. Every material has a value for that and it effects but is in no way related to the frequency.

So what do I do and do I use any of this stuff in my building process? Well yes, the first thing is I have a love of how things work and as such have studied and researched musical acoustics for quite a long time. The more I do the more I am persuaded that despite the undoubted physics behind the subject there is so much going on that in practice it is more akin to alchemy than engineering. I do support that you learn at least the very basics of materials science and musical acoustics because with those you can understand just about everything that happens when you build or play a musical instrument. You won't be able to predict your results but you will be able to control them by using simple techniques.

For me the most important relationship is that between mass and stiffness and is one that you can control. When I select timber I might tap it in several places to get an idea of the quality of the tone not because that will translate in the finished instrument but because it gives me a good idea of the mass and stiffness. When I'm building I do tap when I'm carving archtop plates but again I'm not listening for a specific frequency, more a type and depth of tone and to get an idea of how quickly the tone is shifting also to find out where the strongest nodes are around the bridge area. Again I'm playing with the mass and stiffness not tuning to a note. Does it make I instruments better. I have no idea but I am convinced that it makes them more consistent in quality and tone.

Essentially what I'm saying is that musical acoustics is a hugely complicated but rewarding subject in itself but at your level of experience don't get bogged down in the detail. Sure tap away and take notes about what you hear as you go and how it changes. It's that knowledge that will eventually enable you to use the subject effectively. Any other questions on the subject as a whole or why or what just fire away.
 
Light said:
Nope, don't do it. Not even when I'm making acoustics. The basic premise of tap tuning is to make your guitars more consistent, but as near as I can tell the builders who do it have the same level of variability as those of us who don't. And the most consistent guitars I know of (even if I don't like them) are Taylor guitars, and if you think Bob Taylor is going to waste his time on tap tuning, you are kidding yourself. Bob's goal is to get every guitar in and out of the factory with less than 15 hours of labor. Tap tuning isn't part of that equation!

Muttley will probably come along and disagree with me soon, as I believe he is one of those tap tuning guys.


Light

"Cowards can never be moral."
M.K. Gandhi
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;) With you on the Taylor thing but IMHO thats because they have engineered OUT much of the factors that make the difference.;) But no, as I said I don't tap tune. I do tap and flex as I go though. Flexing the top is a good way of judging the stiffness which is what we are after in the end. It is one of those arguments you could have all day and despite being routed in science there is no right or wrong way or definite proof of the engineering of it.. That's the beauty of it.
 
Thanks so much for taking the time to reply. I really appreciate it. I'm going to keep taping and taking notes. For such a simple thing (a wood box) the acoustics of a guitar are complex and mysterious to me. It seems the more I delve into building the less I know but thats what makes it so damn cool.

Muttley I did a search for Chladni plates and did a quick experiment with some cardboard and tea leaves. Whoa! Thats amazing! I don't have any unglued tops to experiment with so...yeah I'm going to need more wood.

Thanks again
 
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Milnoque said:
I would love to hear more about your project Violent5. Pix would be nice too.
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Well this project is my first dreadnaught build. It has curly mahogany back and sides with a sitka spruce top. I made a two piece mahogany neck but bought a preslotted fretboard (gibson scale). I just finished binding the body with herringbone and curly maple. For the rosette I used abalone and some black/white wood purfling. I'm waiting on a delivery to do the fretboard inlay so I can finish up the neck.

My brother started a 12 string dreadnaught build for a good buddy at the same time. Its curly maple back and sides. He started 3 archtops too. I havent taken any photos. I always feel to busy to grab a camera but I guess I should sometime.

My son works with us on these projects and wants to start a build of his own when we finish these up. He saw a couple of pieces of cocobola locally so I think we'll go have a look at it this weekend. Any downside to cocobola for a back and sides?
 
One thing Muttley said, which I forgot to mention, is I get a lot more out of flexing the wood than out of taping. I'm OK at it, but my dad (who is something like 500 acoustics ahead of me) can tell a lot about a piece of wood by flexing it, and depending on what he is after will sand tops and backs thinner or thicker. He doesn't tap, but he definitely flexes.


Light

"Cowards can never be moral."
M.K. Gandhi
 
Hey guys I have another dumb question. My brother says he wants to raise the tapped pitch of one of archtop backs he's working on. He thinks adding a brace to the back of the carved maple back will stiffen it and raise its resonant frequency. I told him I didn't think I would do that so he suggested I ask here and see if you guys think adding a brace to an archtop back to alter its resonant frequency is ok or a no-no. What do you think?
 
Violent5 said:
My son works with us on these projects and wants to start a build of his own when we finish these up. He saw a couple of pieces of cocobola locally so I think we'll go have a look at it this weekend. Any downside to cocobola for a back and sides?
Click to expand...

Cocabola is a true rosewood (dalbergia sp.). It is closely related to Brazillian rosewood and shares many of the same properties. It can be strikingly beautiful.

It has a high oil content and tends to gum up your sandpaper. Be especially careful with your glue joints. The oil in the wood can effect their integrity.

People seem to have an allergic reaction to cocabolo more than any other wood commonly used in guitar construction. Make sure your ventilation is good, wear a mask, and keep the dust cleaned up.
 
Violent5 said:
Any downside to cocobola for a back and sides?
Click to expand...


Only that I can't be in the shop when anyone is working with it.


Violent5 said:
Hey guys I have another dumb question. My brother says he wants to raise the tapped pitch of one of archtop backs he's working on....

{snip}

...What do you think?
Click to expand...


If he doesn't like the sound of his guitar, he should buy a different one. Trying to turn an existing acoustic guitar into a different one is a total waste of time, and will pretty much always fail utterly.



Light

"Cowards can never be moral."
M.K. Gandhi
 
Light said:
Only that I can't be in the shop when anyone is working with it.
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Haha I didn't know there was a good chance we'd all be allergic to it, thanks for the heads up.



Light said:
If he doesn't like the sound of his guitar, he should buy a different one. Trying to turn an existing acoustic guitar into a different one is a total waste of time, and will pretty much always fail utterly.
Click to expand...

This back is freshly carved and not glued to the sides yet. He thinks its tapped tone pitch needs to be raised. This particular piece of maple has always had a lower, deeper tapped tone than the other two he carved at the same time. He wants to add a brace to it to raise its pitch to be more harmonious with the pitch of the top he has carved for it. I'm not sure adding a brace to an archtop back as a tone bar is a good idea.
 
I don't remember ever having seen an arched back instrument with a brace installed so I have no basis for an opinion on how it would affect the final tone. That having been said: Adding a brace would effect more than the pitch of the plate. It would change the basic patterns of the vibration. I'm also concerned it may have a dampening effect on the plate's ability to efficiently vibrate by mechanically coupling it to the edges. I don't know how pronounced the effect would be.
 
Milnoque said:
I don't remember ever having seen an arched back instrument with a brace installed so I have no basis for an opinion on how it would affect the final tone.
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Yup, I'm with you. I don't know enough about how it will adversely affect the back to justify adding a brace nobody else uses. It seems smarter as a novice builder to stick with tried and true techniques. I think my bro is pretty determined to do it however. I guess we could remove the brace later, it would be a hassle but not too bad.

Thanks
Violent5
 
Violent5 said:
This back is freshly carved and not glued to the sides yet. He thinks its tapped tone pitch needs to be raised. This particular piece of maple has always had a lower, deeper tapped tone than the other two he carved at the same time. He wants to add a brace to it to raise its pitch to be more harmonious with the pitch of the top he has carved for it. I'm not sure adding a brace to an archtop back as a tone bar is a good idea.
Click to expand...


Have him go back and read what Muttley said - there is no way to predict what that will do to the sound, and in particular there is no way to predict if it will be a good thing.


Light

"Cowards can never be moral."
M.K. Gandhi
 
Violent5 said:
Yup, I'm with you. I don't know enough about how it will adversely affect the back to justify adding a brace nobody else uses. It seems smarter as a novice builder to stick with tried and true techniques. I think my bro is pretty determined to do it however. I guess we could remove the brace later, it would be a hassle but not too bad.

Thanks
Violent5
Click to expand...

As a novice builder I would think he would be as interested in the results he gets from a back with a lower pitched tap tone as he would from the brace experiment. Maybe he just wants an excuse to try a brace on his build.

Muttley and Light (both of whom are far more experienced than I am) are in agreement that they don't use the tap tone tuning on their builds. I was taught to use tapping when I was learning but pitch wasn't the emphasis. I say tell him what you think and let it go. It's his experiment.

I would offer that the behavior of a brace on a curve is very different from a similar brace on a flat surface.
 
Milnoque said:
Cocabola is a true rosewood (dalbergia sp.). It is closely related to Brazillian rosewood and shares many of the same properties. It can be strikingly beautiful.

It has a high oil content and tends to gum up your sandpaper. Be especially careful with your glue joints. The oil in the wood can effect their integrity.

People seem to have an allergic reaction to cocabolo more than any other wood commonly used in guitar construction. Make sure your ventilation is good, wear a mask, and keep the dust cleaned up.
Click to expand...

Satinwood is the one I won't have in the shop. For really oily woods I wipe over with naphtha a few times before glueing or finishing.
 
Milnoque said:
I don't remember ever having seen an arched back instrument with a brace installed so I have no basis for an opinion on how it would affect the final tone. That having been said: Adding a brace would effect more than the pitch of the plate. It would change the basic patterns of the vibration. I'm also concerned it may have a dampening effect on the plate's ability to efficiently vibrate by mechanically coupling it to the edges. I don't know how pronounced the effect would be.
Click to expand...

There are some that have back braces. They tend not to be used these days except on the cheaper ply construction methods or pressed backs.

The effect on the finished sound is impossible to predict. It will stiffen up the response and my best guess would be that it would lead to a tighter and focused high end at the expense of the mid an lower range. You would have to try it to find out and that would be a hell of a lot of breaking down and reassembling.
 
Violent5 said:
Hey guys I have another dumb question. My brother says he wants to raise the tapped pitch of one of archtop backs he's working on. He thinks adding a brace to the back of the carved maple back will stiffen it and raise its resonant frequency. I told him I didn't think I would do that so he suggested I ask here and see if you guys think adding a brace to an archtop back to alter its resonant frequency is ok or a no-no. What do you think?
Click to expand...

Sorry for the late response. I've been on one of my annual wood hunting jaunts so been away from the home for a week or so.

To answer, there is no way he can predict the effect of adding a brace to the back. I would suggest that unless he has made at least 50 archtops he shoul work on his tool skills first and just record the results of how things turn out. There is just too much going on acoustically to accurately predict the effect of such tinkering and I doubt he has the required experience to be able to control what he wants to achieve. You can multiply that figure quite a few times for me and I'm still learning. I can play around with the stiffness and mass to get close to the sound I want but not always. I wouldn't approach it the way he is.. Re read my earlier post and get it to him as well.;)
 
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