Official Luthiers Forum!

I've hit another poison thread: every time I try to reply I get dumped. After five tries yesterday and three today, I'm starting a new thread.

It makes some sense to think that the condition of the 'free' plate has some relationship to the way the completed guitar sounds. If that is so, then any sort of test that gives you valid information about what that plate is doing should have some predictive value.

The problem is that going from the 'free' plate to the assembled box in any sort of rigorous way is extrememly difficult. There is simply no way I know to 'prove' that a certain Chladni pattern or tap tone frequency leads to a given outcome on the finished instrument. All we can do is come up with methods that we think ought to work, and then find out whether they do or don't by making lots of guitars and seeing if we get consistent results.

Those of us who have been using Chladni pattern testing have found that we do get pretty consistent results. I'll note that, as far as I can tell, the shapes of the patterns are far more predictive than the frequencies, and I believe Mark Blanchard has the same impression.

You can, to some extent, 'hear' these shapes: tops that have well-closed 'ring+' modes tend to sound 'clearer' when tapped than ones that don't, at least to me. Then again, remembering Feynam's Dictum, I may be fooling myself.

Bourgeois uses 'tap tuning' in his production, but I think that Chladni testing is probably too time consuming for even a small production shop. Maybe if I were tuning twenty a day I'd get quicker.

This is one of those instances where it's hard to do good science. Not only is it extremely difficult to isolate variables, there's also no agreed on way to measure the outcome. I think I make better guitars with Chladni testing, but just what is 'better'? All you can do is make lots of guitars, and get lots of folks to play them, and see if they don't suck too badly.

Alternatively we can try to build a few guitars that really suck and see what the Chladni patterns tell us. Have you ever run a Chladni test on an Ovation, Alan? Or maybe pulled the top off of one and tested the plate itself?

How about pulling the tops off of some materially identical but different sounding guitars and testing those? It seems to me that working backwards could yield a different angle of results, but there are obviously some problems involved (having to pull tops off of completed guitars, the differences between a top before gluing and after removal, etc...).

Definitely agreed on the difficulty of doing hard science... Perhaps if we were able to build an extrapolative dataset of Chladni patterns and resulting sound of guitar, we could then subject customers to a sound sample assay to quantify exactly what characteristics they wanted, then pick a Chladni pattern to suit.

Just musing on the subject... it's very interesting to me!

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Evan McCartney

Thanks Alan I was waiting for your response and when I didn't get one I suspected you were actually building guitars or had problems with posting.

"Does the tap tone or Chladni pattern correlate with the sound of the finished instrument?" That was my question that you couldn't reply to. Your answer was noted.

But there is some limitations to what the tap tones might correlate with difinitively. Clarity is a term that has (clear) meaning IMO. A guitar with good clarity will exhibit a certain modal density or high amplitude in a range of frequency that makes it sound clear. This is most commonly in a much higher range than anything that the free plate lower tap tones exhibit. Not to be argumentative, if you hear something then it IS there and I don't dispute that, but I read so many comments here about how tapping on the plate leads to this or that. Or "voicing" concepts, even some that are exclusive enough to be only available by extensive training, for a fee of course.

Okay, here is my point iin a nutshell, or I guess question. Are the (main) tap tones of the free plates any value besides defining the lower end of the guitars output? Is there anything like Dunnwald's numbers for guitars?

http://www.akutek.info/Papers/AB_Geometrical_measures.pdf

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Ken

Ken McKay wrote:
"Clarity is a term that has (clear) meaning IMO. A guitar with good clarity will exhibit a certain modal density or high amplitude in a range of frequency that makes it sound clear."

One study I heard of made the point that everybody is perfectly consistent in the way they use terms like 'clarity', but that not everybody uses the same term in the same way. Your 'clarity' may be somebody else's 'eveness' or whatever. I rather tend to agree with your difinition, although I'd say something about the peak-dip ratio between output peaks as well. I tested one guitar that had quite a high output in the 2-4 kHz range, but it was 'flat', and the instrument lacked 'clarity' or 'sparkle'. Plywood top.

" Not to be argumentative, if you hear something then it IS there and I don't dispute that, but I read so many comments here about how tapping on the plate leads to this or that. Or "voicing" concepts, even some that are exclusive enough to be only available by extensive training, for a fee of course. "

Certainly. THe problem is to figure out how to measure it. As for the sorts of wide-ranging claims that one so often sees, I recurr to Feynman's Dictum, that you are the easiest person for you to fool. We all tend to hear what we think we'll hear.

"Okay, here is my point iin a nutshell, or I guess question. Are the (main) tap tones of the free plates any value besides defining the lower end of the guitars output?"

I believe so if you look at mode shapes rather than frequencies. This is based on several different experiments that involved 'blind' judgements of the sound of completed guitars that differed in the 'free' top mode shapes.

" Is there anything like Dunnwald's numbers for guitars?"

That's a seperate issue, and so far as I know the answer is 'no'. Nobody has gathered the large data base that it takes to come up with those criteria: Dunnewald tested 700 violins! Not everybody in the violin world accepts his conclusions, either.

I have a colleague who also makes double basses. He uses Chladni patterns and I use tap tones, but both in an investigative way. Neither of us know for certain how the test applies to the finished instrument but no doubt we are learning how to make them better. Or ...fooling ourselves.

I know that some reject Dunnwalds regions of describing violin sound but it is really hard to dispute it unless it is totally dismissed. The actual wording of clarity and nasal and brightness are maybe a little subjective but it is pretty easy to listen to violins and be able to describe a sound in Dunnwalds terms. The human ear is remarkable in this way. It is easy as distinguishing an ee from and aa sound. Another thing that is also clear is that with violins there is a GOLD standard to try to attain. That could be either Stradivari or Old Italian or Guarneri and is most distinguishable in the drop off in the brightness area with good violins, thus avoiding a harsh sound. This in conjunction with a very strong depth of sound in the L region.

Analysis of guitar sound by numbers might be a little more difficult but not impossible and certainly not 700 guitars are necessary to develop some stats do describe it. Classical guitars would be perhaps easiest and more useful since their sound is expected to do a certain thing. But I could see that OM, versus Dread versus other shapes could be defined also.

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Ken