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OK, folks I'm naturally a cynic.

I'm a doubting Thomas, but I can be persuaded.

I've read Siminoffs great book on tap tuning. Obviously the guy knows what he's talking about.

a resonant instrument will sound better than a non resonant one. I fully accept that.

BUT

I'm making my first acoustic guitar top.

My 7th acoustic instrument mind you.......

and as I was shaving away the braces it struck me.

If I tune this top to thud at 440.

then I stick it onto the sides.....

and carve off the extra 1/4" all the way round, then it's not going to be 440 or any octave harmonic or anywhere NEAR that is it?

then once the bridge is stuck on, that'll throw it farther out.

then the finish will potentially throw it ever FARTHER right?

and then a nice pearloid pickguard takes it out of the ballpark alltogether won't it?

Now I'm a reasoablty inteligent guy, with a better than average understanding of the physics of resonance (I've been known to teach highschool science.....)

so come on, someone tell me I'm wrong and that I'm not the first kid to spot that the chubby little emperor is running around in the buff!!

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My soundclick xx luthier blog xx luthier soundclick

You are correct that the top will change when glued to the rim. but I don't believe that Siminoff said the top would resenate at 440 when attached. Rather that the free top should resonate at 440 this is only one person's method, and many tune free tops to differnt pitches to achieve the sound they want based on their experiance and their constuction, bracing and many other factors. But to reiterate you are correct in thinking that a free diaphram will resonate at a differn pitch than the bound diaphram.

The thing to keep in mind is if you do not tune to something based on prior data then you are taking a crap shoot on what you will end up with.

Prior experiance from someone else is good starting point but you really need to keep data form each build. Over time you will work out using this data, what works best for you. This is a good time to think about keeping a daily build journal. MichaelP38895.468125

Ahh, what a great subject to discuss *rubs hands in glee*

The top will also be affected by humidity changes, which will alter the pitch of the tuned top too...

I read an article in the
Cumpiano Newsletter about tap tuning three days ago, as I was carving my back and top braces..I too was wondering about this mysterious art...

But what about the back too??

I actually spent a lot of time tapping my rosewood and spruce back and top before the braces were glued on. They already had a resonant quality to them, the back more then the front had a bassy quality to it...

I was delighted when I started carving the back braces..when I had finished, tapping the board produced a sound that seemed to have "grown"..the basses were still there, but there was a strange decay to the basses, they dissolved into higher "tinkly" tones...I took them to my spouse to hear, and he was amazed...

I suppose it was due to the stiffness of the wood plus the braces..

I then proceeded to carve the spruce top braces, bearing in mind I wanted the braces to still have structural integrity, but a similar tap tone...

All I can say is that I carved away until I heard something I liked.

A guitar's tone can certainly be improved by enabling the instrument to be as strong and light as possible.

I guess my conclusions would be the same as Sr. Cumpiano...it cannot be explained properly, because nobody really knows for sure!



Sam Price38895.5005092593

I have discussions with both Siminoff and Cumpiano on this very topic and offer these observations. Although they both tune their tops in their own manner they are both looking for the same thing, the 'sound' that they want out of their own guitars. As Michael said above, start at someone else's starting point, Cumpiano, Siminoff, standard Martin Bracing, anything, and then just keep good notes as you adjust over subsequent instruments until you have what you like.

As for Siminoff. You really need to understand that his process is a collective and the end point is the adjustment of the aperature (soundhole) size to bring eveything back into sync. I like Rogers methods in that they force you to think in a scientific process and thereby record your efforts and results, taht can only help you in the future. And remember A440 is today's concert pitch, it was much different in early 1900's when Llyod Loar started doing a bunch of this work and it will likely be different again in future. Roger told me that there is a movement to have it moved to something A444 or something...I don't have my own notes handy .

Shane

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Canada

Yup. You are correct :D

As a total newbie at the subject, I can't tell you the science of what I did, just that eventually, keeping in mind the structural integrity of the braces, I tapped and carved the tonewoods eventually sounded "right", hence I stopped...

I'll guess I'll leave the tuning lark up to the bridge and neck placement and how much success I achieve with creating good intonation!!!!

Sam Price38895.555474537

I tap and carve trying to achieve a constant tone, what ever that may be, all the way around the lower bouts, from the top finger brace around to the other finger brace. If and when I get the tap tones to sound the same, im done. I then glue the top down, and after bindings I sand the perimeter to release the top, feeling for a flexibility at the bridge location with my trusty thumb Right or wrong, Im happy with the results, and more importantly, I seem to be getting consistant results.

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Lance@LuthiersForum.com

Good timing on this question.

I just read Benedetto's book on building arch top jazz guitar. He pretty much supports what has been written above.

1. Tap for resonance and "the sound" that is ill defined but aquired through practice.

2. The fundamental tone will change when glued to the body, bridge etc.

Two related questions;

1. Tap tone and carving a top for a bass guitar....
I assume the resonating breadth of frequencies would still be the goal but is there anything specific to avoid?

2. What is the optimal top thickness for an acoustic bass guitar versus the jazz guitars Benedetto makes? Do I need to go thicker for bass?

3. While I don't have an osciliscope I do have an RTA (real time frequency analyzer) that I could do some analysis on the tip with either a mic or soundboard transducer during carving and assembly. Since this is my first acoustic project and I don't have an ear for tap tones are there some things I could look for on the RTA?

Sorry for the big can of worms LOL but hey thats what we are here for at OLF right?

This is always a fun topic, you will find people all over the map on this one, but I like the way you are thinking. I don't think enough people (In general not here on the OLF mind you) stop and think things through to their logical conclusion.

For me this is like using a digital scale to measure out exact ratio's for mixing hide glue, once it's heated and ready to use your ratio's on a constant move as water evaporates, why worry about?? Just keep it thin enough to use

Like a lot of builders I tune my top to where it resonates at a tone I want to hear, it's something I've learned from building not something I can quantify in words. Once there I glue it on the rim and when the body is sealed and the binding it applied I work on thining the edges of the top (and back) until I get a good deep tone from it.

I've stayed on the organic side of tuning but I'm starting to dabble a bit with measuring resonance and other things on my tops (braced and unbraced) and have considered doing some Chladni testing to see what kind of results I get (I blame it all on Al Carruth ).

-Paul-

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-Paul-

Patriot Guitars

[QUOTE=Sprockett]
I've stayed on the organic side of tuning but I'm starting to dabble a bit with measuring resonance and other things on my tops (braced and unbraced) and have considered doing some Chladni testing to see what kind of results I get (I blame it all on Al Carruth ).
-Paul-[/QUOTE]
See,This is what I love about building guitars.There is always differant things to do and try out. It makes it FUN! Yep,Its all Al Carruths' fault

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Anderson Guitars
Clearwater,Fl. 33755

Mea culpa! Well, actually, it's Carleen Hutchins' fault, with an assist from Fred Dickens....

I've been using 'glitter patterns' for a long time, and keeping records of stuff all along, although I have to say the record keeping gets better all the time. To me that's the main thing: no matter what system you use, keep records. Eventually you'll notice something, or come up with some harebrained theory [they're all harebrained] and the data will help you check it out.

My data [FWIW] indicates to me that the _shapes_ of the resonant modes are probably more important in determining the final tone than the pitches or pitch relationships. Sometimes very small differences in mode shape can have clearly audible results when there seems to be no other difference. Often you can 'hear' good free plate mode shapes: they tend to ring better.

All of this is hard to justify in strict physical terms. As has been pointed out, many things change when you glue a top to the rim. The most important change seems to me to be that the edge is simply made rigid, instead of being flexible. Any mode that involves bending around the edge is gone once you glue it down. Another is that the impedance at the edge goes from effectively zero [voltage=force model] to very high, so the phase of reflected wave fronts is changed. If the ring-type 'free' plate modes are well 'closed' then neither the impedance nor the stiffness changes will effect the shapes much, except that the node lines will shift owing to the reflected phase difference. What the heck; it's a theory.

The problem is checking it out. You can make a lot of guitars, but that takes a lot of time and money. Besides, you have to make some of them deliberately 'bad', and nobody can afford to do that for long. I have finally designed an experiment to test some of this stuff out, but it's hard to find time to run it, and one _really_ could use a holographic imaging system of some sort. Sigh. Can anybody think of a way to link the study of guitar acoustics to Homeland Security? Then I could get some funding.....

Martin,
   I appreciate your "Emperor's clothes" view of this process and it is true in many respects....until you have enough guitars under your belt to have been able to document and understand what happens to a top's resonant frequency when it is finished. After the finish, with more and more guitars in your completed projects stable, you will be able to more accurately predict and understand what the mass of the bridge being added to the mix does to it in this continuing saga of wandering from the original tap tone that we work so hard to attain.

    After the mass of the bridge is glued on and the finish has taken its toll and shown its effects on the top's tap tone, we shove strings through it all and pull them to concert pitch creating a matrix of tensions and torque forces that present all sort of distortion effects and resonant effects that vary infinitely from guitar to guitar. It's a fascinating endeavor that will never stop amazing and surprizing you...if you continue to care and don't just settle into a set of default bracing placements and dimensions that have proven themselves to provide generally good results.

   I've built nearly 500 acoustic guitars and have been a proponent of tap tuning since guitar number one. I've always understood that the mass of the bracing in combination with the mass of the top is important to the resonance and sustain that can be achieved. The whole prospect can't end there, though.

    Many builders fail to recognize and address the additional importance of the distribution of that brace mass and subsequent weight and simply tune to a generally resonant tone as they tap the top and shave small slivers of wood from carefully selected braces or equal amounts of mass from the braces in passes around the top until they believe that they've coaxed the assembly to what is very close to its resonant potential. The violin builders who have been revered as being the greatest of all time were careful to consider this aspect of mass distribution and the assymetrical thickness graduations in the top and back plates of their wonderful instruments is clear evidence of it. Viloins worth millions of dollars have been restored or repaired over the years and I've had the honor and priviledge of being able to spend a little time in the presence of a few while they were being worked on. A surprizingly wide variation in the thickness of the top and back were measured from any point in one half of the plates to the symetrical point on the other half.

   The goal was mass and weight distribution that would create balance, sustain and the correct resonant frequency in the closed chamber of the body. Some may disagree with this theory, and they have every right to apply their own if it's proven itself to yield the same results.

   The tuning of a top begins...for me...with the matching of the top to braces to it according to their respective resonance characteristics. Tops and braces are all separated in my shop according to whether they have a generally "low", "medium" or "high" natural resonant frequency. With a top having a specific resonant frequency, I consider the desired tone of the future owner of the guitar and align the top with a set of braces that have a resonant frequency that will compliment and steer its tone in that desired direction while providing significant balance to the resonance of the components as they're joined to become the braced top assembly.

    When you tap tune a free standing top, you should never tune to a particular note since it will disappear when that top is joined to the back and sides to create the resonant chamber of the body and the note that it resonates at. It's that chamber that needs to be tuned to a note reading. All of the great classic guitar builders as well as their violin building counterparts....from the greats down have had the goal of an accurately tuned note being evident in their closed instrument bodies.

   With every instrument that you build, you'll be able to experience and document the effects of the subtle variations that you implement and use those results as a foundation or starting point for your next. I never tune my bodies to a resonant concert pitch "A" since it would create a resonant nightmare with the harmonic blanket being dominant and even difficult to control. I shoot for a resonant point as close to an F# as possible. It's relative to the A and provides a harmonic blanket that not only submits nicely to the fundamental while providing complexity, but also aids in the avoiding of ghost notes or detuned harmonic presence.

   Most players who have a discerning ear can tell you that they've experienced, at one time or another, at least one guitar that just didn't sound in tune even though the intonation was on and the strings were pulled to their correct pitches. The lack of tuned harmonics in relationship to the fundamental note plain can be caused by several factors like string flaws or defects, but can be contributed to by the lack of balance and alignment of the resonant characteristics of the guitar body itself.

   Alot the processes and the methods that we use to achieve our common goal of great sustain, volume and tone with a nice balance between the fundamental and harmonic blankets in the completed guitar are cryptic and can appear futile at times, but we need to closely document the results of our efforts after having documented the dimensions and methods that we use to get those results.

    I have a thick book full of notes that include every guitar that I've ever built. It wasn't until my 50th guitar or so that I decided to create a spread sheet listing all of the dimensions and steps in the process so that I could have a more efficient system of documenting things that was also much easier to read when I went back to refer to it.

   Tap tuning is a very real and important step in the overall tuning of the guitar's body and the quality of the tone that it will be able to create so don't discount its viability yet. I advise that you pay close attention to what this guitar becomes and use it as teacher in preparation for your next guitar....your sophomore experience in this education that lutherie is.

   Most importantly as you build and grow and learn with each guitar, enjoy the process and the results...and the challenge that the next set of woods present.

Regards,
Kevin Gallagher/Omega Guitars   Kevin Gallagher38902.4467476852

Is that F# as a free plate or as an attached plate?

Michael,
   Remember that alot of the subtle nuances and changes that occur in a top while being tuned can be hard to detect for someone who hasn't experienced it with many tops so there is a curve of development of both your ear and your technique for it. Be patient and really pay attention to what happens throughout the process and, just as importantly, take notes and draw diagrams and take some more notes...then draw a few diagrams and....it can;t hurt to take a few more notes.

   Did I mention that notes are important? They help you to refer back to the results you've enjoyed in past guitars or results that made you cringe in past guitars so that you can avoid the latter and do better on the former next time.

   When we tap tune tops, we're never tuning to a note, but looking to coax the top along with its bracing as close as possible to its resonant capability with strong consideration being given to sustain and the balance with which it vibrates when excited (by tapping in these cases) in all areas. Another key consideration should be distribution of vibration to the nodes or nonvibrational areas by the bracing system in order to ensure that the entire plate is active and easily excited by the string vibration originating at the bridge and being disbursed from ther to every square inch of the top.

   You'll find as many theories about and approaches to tap tuning and brace efficiency as you will luthiers willing to talk about it so you have to take them all and choose what will work for you and can prove itself to you and discard the rest and leave it to the guys who have embraced it. Experience is the best teacher in these areas as in many, but it helps to be able to refer to the experiences of others to possibly cut some time and headaches out of the equation.

   The F# is the actual resonant note of the closed body under string tension that is goal for the completed instrument. To achieve it, though, the steps leading up to that point need to be monitored and documented to form a system of prediction for the finished guitar. I don't look to register aprticular note for the tuning of any of my plates free, but shoot for what is a familiar and proven resonance that enables me to assemble a body and end up with the resonant frequency being very close that F# mark.

    I'll look for a very interesting video clip that I saw a while ago on tap tuning and the general tuning of the body chamber of the guitar. When I find it, I'll drop the link here. I'm waiting to be able to get the entire video to see the guy's emtire presentation.

Regards,
Kevin Gallagher/Omega Guitars

    Remember that it isn;t necessailary the resonant characteristics or notes of the individual plates ad components that generate the actual note that the close, bound body taps to. It is more determined by the volume and shape of the chamber that they are joined together to form.

   You can spend hours tuning a top and back to a particular note only to have those notes disappear immediately upon their being glued to the sides.

   Try to coax them to a point where you believe that they have reached their potential as far as balance and sustain and they will be allowed to respond to and be excited by that body's fundamental note when it is prompted by string vibration in the completed guitar.

Just an afterthough to my previous post in this thread.

Regards,
Kevin Gallagher/Omega Guitars