Over the last few weeks I have had some VERY interesting phone conversations with different luthiers, some of them participants of the OLF. Somehow, the following discussion always seems to arise, so I thought I would post my thoughts and then see what kinds of responses it recieves.

I am going to be real up front with my first statement: I dont buy into the tap tuning theory. There, I said it and I mean it!

We are not making bells, we are making speakers. Here is the basis for my argument boiled down to some real simple terms: You can design the best bell in the world (start reasearch here), but if you sit that bell on the ground and eliminate it's outer edge from vibrating, you have killed the bell. You can create a guitar top that rings like a bell (in effect it *is* a wooden bell) and then glue it's outer edge to a stiff guitar rim, you have just killed all of the qualities of the bell.

Dont get bent out of shape yet ! read on....

I will agree that if you take the time to tap tune your guitar by thumping it , you have most likely reduced the mass at the outer edge of the top, including the thickness of the top and also the brace thickness (and strength) at the outer edges. The mass at the center of the top has more or less remained constant, agreeing that minor variations are accepted.  I think that we should be studying more of the reponse of the acoustical speaker technology (begin reasearch here) and adjusting our efforts on how to project sound as though we were building a speaker rather than a bell.

At some point in the making of a speaker, you have a center core that is fairly rigid at the point where vibration is induced. In the case of the speaker, this is achieved with electromechanical means.... in the case of the stringed instrument, this is achieved  with the vibration of the strings. Same principal, different source of vibration.

In the cone of the speaker, you can adjust the rigidness of the cone in concentric circles and greatly affect the frequency response of the final product.  Some manufacturers achieve this by placing rigid concentric circles at different distances from the main center of the cone, some make the cone material thicker at the center and progressively thinner toward the outside. Almost all manufacturers of speakers have gone to a rubberized material on the outer edges of their speakers which greatly increases their ability to move air even in the smallest of speakers. The placement of the ridigness (is that a word?) shows its effects by adjusting the frequency response of the speaker.

If you apply this thinking to the guitar, the top bracing of the guitar's braces will affect the overall frequency response. By scalloping the braces, you have created rigid spots in the top's  vibrating surface (or cone of the speaker) and you have shaped the tonal qualities of the sound by trimming some frequencies while allowing others to remain. I will agree that bell manufacturer's also use this thinking to shape the harmonics of their bells by grinding certain spots on their bells.

We can adjust the frequency response of the guitar (or bell or speaker) by moving the rigid spots in the surface of the top of the guitar. This will apply to parabolic bracing as well because we can move the point of arc of the brace inward and outward toward the outer edges to "clip" certain tonal qualities and harmonics.

Am I saying that tap tuned guitars dont sound better?

No! by all means this may be achieving the same result as just thinking of the guitar as a speaker rather than a bell. Some of the same principals apply to each.

When I decide on a guitar top's thickness, I am thinking of it as the "cone" of a speaker (not a bell). I will decide on how much reflex I will allow by adjusting this thickness. After that decision has been made, I can then adjust the bracing into a pattern that will allow for maximum rigidity at the core and then further adjust the harmonics of the guitar's top by deciding on the spots of rigidity to shape it's harmonics and frequency responses.

Either way you go about thinking of how you shape your top, the end result may be similar. What I am trying to say here is that we are not making bells. We are working in a very limited range of the human ear's ability to hear and we are projecting sound over a wider range of frequencies than any single bell can achieve.

One more thing. I think of Tim McKnight's "double backed" guitars somewhat like the BOSE speaker technology. By adding the second back to his guitar, he has in effect created some echo chambers of differing sizes which is allowing very minute delays of sound to transfer to the top. I applaud Tim for his innovative thinking! He now has me thinking that one could actually use this space to create a "micro chamber" similar to the BOSE speaker system. I'll have to give that some thought...I would love to be able to play and study one of  his double backed guitars.

The end result...

In no way do I mean to discredit the years of research by masters of the trade that have adopted tap tuning as their standard.  What I am saying is I dont beat on my guitars unprotected top wood trying to get it to ring like a bell. I dont want to compress the cell structure of the top's wood even in minute amounts. As you can see, the outcome of tap tuners may be similar, but my way of thinking and building guitars is a LOT different. Thanks for reading

Ken

Ken

You bring up a point that I had almost forgotten Rick.

Sometime in my years of research on tops, I came across a web page that discribed a form of tuning where the luthier used glitter sprinkled on the top to create a circular shape (sorry, but I cant remember who the luthier was). If I were to be truthful about my reasoning for tuning a top, I think this theory would probably be one of my greatest influences. He would shave braces until he could get the glitter on top of his guitars to form a circle on the lower bout. I am pretty sure that this was done after the guitar was completely built, or at least the box was built. To me, this makes a whole lot more sense than simply tapping on an unglued top to hear it ring. I dont use the glitter test, but I do use some of the principals of this method to tune my tops.

I know that I can easily surpass the tonal quality and volume of one of the largest guitar factories on a consistant basis, so I know I am on the right track. I do have a few tricks up my sleve on building guitars though. Some of what I know I learned from a master of the craft, some of it I got from reading volume after volume of information and then putting what I had read to good use to come up with my own "system".

I just hate to see so much emphasis placed on tap tuning, especially for new builders, because I feel it can lead them astray if they arent careful. If one just thinks of the top of a guitar as a speaker cone that has to be braced in order to keep the top form warping under the torque of the bridge pull, then it is much easier to get the final result that most people are seeking.