The Difference Between An Archtop and Flat Top

[kenbennett]

The whole tap tuning thing is interesting, because Bob Benedetto doesn't seem to think its actually that important. He claims its something that luthiers do but is a little bit like a red herring. They do it cause they feel they have to, or should but not that it makes any difference.

"to the inexperienced ear, these subjective terms may mean nothing (ref tap tuning) and could even be misleading. I therefore encourage the beginner to go through the motions of tapping and listening as described"

"I believe there is no such thing as a bad tap tone and would never discard a piece of wood for that reason".

Bob Benedetto (Making An Archtop Guitar)

You are exactly correct. However, the fact remains that, before bracing, an archtop top plate has a clear fundamental pitch (with no consensus on what that pitch should be and no way to really predict it) and the flat top has a less defined fundamental pitch (or a pitch that is so low that you hear more of a rumble than a specific note).

My point is that this is simply one general difference between flat tops and arch tops, one that may be a contributor to the difference in tone.

A luthier trying to explain his art in terms of acoustical science is like a recording engineer trying to explain why tubes and analog tape sound good. They simply don't know. The luthier and the recording engineer have learned through training and/or experience how to manipulate their tools and materials to get a good result. Why it works is for the most part outside their scope. It's interesting to speculate but not essential to the work.

[kenbennett]

...

As for tap tuning, Jim Triggs doesn't do it. When I ordered a guitar from him some years ago, he said that tap tuning could mislead the aging luthier, because a progressing hearing loss of treble frequencies is common as we get older (especially if a luthier is a player too). If the older luthier keeps aiming for the same tap tone - as heard by him - the guitar may in fact end up not sounding as intended.

...

Here we go again. Luthiers should not try to explain acoustics. Triggs is right that we normally loose some high frequency hearing as we get older. However, he is talking about frequencies in the thousands of Hertz, whereas the fundamental frequency of the tap tone that we listen for is only a couple of hundred Hertz.

I predict that frequencies in the range of typical hearing loss of the aging are not even present in the tap tone in amplitudes great enough to be heard by a person even with perfectly normal hearing. I will attempt to prove this hypothesis, just to dispel the myth, on the next archtop that I build by capturing a spectrum analysis of the tap tones in my studio. I will record the tap tones and capture screen shots of the frequency response curves.

Your example about sax players has more merit. Those high frequencies are definitely there in a horn.

Also, I have heard many older people operating audio equipment put way too much high frequencies in their EQ and wondered whether hearing loss was the reason. For the record, I'm 60, but I can still hear up to at least 13KHz in one ear and about 15KHz in the other. When I mix audio I depend on the spectrum analyzer to show me what's going on above that.

[Socalbill]

My experience is mostly with flat tops, and back in the late 90's I had an all day workshop with Ervin Somogyi who is a really incredible builder. He brought 500 spruce top pieces to the workshop and he had them all graded and indexed. He taught us how to find the harmonic nodes in the wood and then listen to the tap tones. Towards the end of the day, he would give us 5 tops and ask us to evaluate which top would best serve a finger style guitarist or a jazz player and we would discuss this in terms of internal dampening and tone. It may not be as important as it seems, but wood varies a lot, especially in terms of its ability to resonate. Some wood rings like a bell while another piece sounds like cardboard. Since then I have felt much more capable of selecting wood for whatever instrument I'm making. Since I don't do it for a living, I can go to a vendor and go through 50 tops to pick one for my project (most commercial builders buy 50 tops and make 50 guitars as the converse example). Listening to the tap tone, running bare fingers along the grain and flexing the piece is valuable in this process.
Bill

Oh and for bananafist: I don't have any pictures on my computer of those instruments. It was long enough ago that I would have used a film camera and those pictures are in some boxes in the attic. If I run across some I will scan then and post.