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Improving Tone With Putty
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=42724		 Page 1 of 1
Author:  Pat Hawley [ Thu Feb 13, 2014 6:01 pm ]
Post subject:  Improving Tone With Putty
I was researching baritone classical guitars and first came across the musician Ralf Towner. He's new to me but he's amazing and worth looking up. His baritone guitar was made by an Australian luthier named Graham Caldersmith. At one point in a video, Graham shows how he is able to improve the quality of a single note by placing a small blob of putty on the top of the guitar in just the right place. Once he finds the spot, he moves the putty to the same location but on the inside of the top and leaves it there. You can check that out here (starting at 1:50): http://vimeo.com/55746044

Anybody around here doing this?

Cheers,
Pat
Author:  uvh sam [ Thu Feb 13, 2014 6:18 pm ]
Post subject:  Re: Improving Tone With Putty
He is probably shifting a mode shape or mode frequency with mass. It is a non destructive way to alter the modes. I believe Greg smallman pioneered the approach, Trevor gore may know more about the history as both smallman and Caldersmith are Aussie builders that paved the way for the application of the scientific method in the construction of guitars
Author:  Clay S. [ Thu Feb 13, 2014 6:23 pm ]
Post subject:  Re: Improving Tone With Putty
Hi Pat,
The first time I ran into this concept was reading Arthur Benade's "Fundamentals of Musical Acoustics". The idea was further developed (by Benade) that after finding areas improved by adding weight (putty), thinning those areas ( or scalloping braces?), making them more flexible, would give a similar result.
Author:  wbergman [ Thu Feb 13, 2014 6:32 pm ]
Post subject:  Re: Improving Tone With Putty
I have a vague recollection of decades ago hearing about this approach used to cure wolf notes.
Author:  Trevor Gore [ Thu Feb 13, 2014 6:43 pm ]
Post subject:  Re: Improving Tone With Putty
uvh sam wrote:
He is probably shifting a mode shape or mode frequency with mass. It is a non destructive way to alter the modes. I believe Greg smallman pioneered the approach, Trevor gore may know more about the history as both smallman and Caldersmith are Aussie builders that paved the way for the application of the scientific method in the construction of guitars

It's pretty much a standard procedure, used by both "scientific" and less scientific makers. It's been going on for so long that I'm not able to attribute it to any particular individual, but it wouldn't surprise me if the technique originated in the works of Robert Hooke (seventeenth century). The advent of modeling clays and poster putty made things easier, of course!
Author:  itswednesday14 [ Thu Feb 13, 2014 6:49 pm ]
Post subject:  Re: Improving Tone With Putty
I usually cant add anything to the threads but Alan Carruth has talked about this for a lot of years.
Author:  George L [ Thu Feb 13, 2014 7:10 pm ]
Post subject:  Re: Improving Tone With Putty
I was playing around with this very idea just last night. I didn't have time to do a great deal of experimentation, but it did seem that moving the blob from one place to another resulted in some subtle differences in tone. It would be interesting to use Audacity to record some tap tests and see what, if anything, is going on. Not sure when I'll get around to it, but it's on my list of things to do.
Author:  Trevor Gore [ Thu Feb 13, 2014 7:58 pm ]
Post subject:  Re: Improving Tone With Putty
Todd Stock wrote:
Works pretty well for panels, but any wolfs on my guitars always cleared up on their own in short order without any further intervention. Be interested in hearing about how it works for you.

Me? Anyway, you got my attention! ;)

Some wolfs go and some stay or just relocate. I had a friend come by just a couple of days ago with a very lightly built traditional fan braced small body classical (far more likely to see problems of this type on classicals) with a very dull note on the C#, 2nd string 14th fret, also evident, but less so, on the first string 9th fret. It moved with re-tuning, so it wasn't a fret problem. A tap test showed a high peak at 559Hz (C#=554.4Hz , so close enough) which signifies high admittance and a likely wolf as a consequence of that. I guessed at it being a cross tripole mode and put some poster putty (less than a gram total) on each bridge end and that moved the problem two frets down. I couldn't get a clean Chadni to identify the mode accurately because there was a lot of top distortion and gravity was having it's usual effect on the tea leaves. I showed him how to use Visual Analyser and he left with some poster putty to play with so he could spend as much time as he wanted to minimise the problem.

There's a heap of ways of dealing with low order resonant modes, but the higher order modes can frequently (but not always) respond well to adding very small amounts of mass so it's a very effective way of finding a solution.

Here's the initial tap response. I didn't save subsequent ones, but the peak at 559Hz relocated to ~500 Hz and lost a lot of height. That was with less than 1 grm of total added mass. The trick is to move the peak sufficient to adequately fix the problem without causing another and I'd be guessing that could be done with ~0.3 grm of added mass. Note to self: must get a new gram scale that has 0.1 grm resolution.
Attachment:
No added mass.jpg
Author:  Shaw [ Fri Feb 14, 2014 1:02 am ]
Post subject:  Re: Improving Tone With Putty
wbergman wrote:
I have a vague recollection of decades ago hearing about this approach used to cure wolf notes.

Yes they still use a similar technique like this on violin wolf tones.
Author:  mkellyvrod [ Fri Feb 14, 2014 10:28 am ]
Post subject:  Re: Improving Tone With Putty
I'll plead ignorance all around on this. I do have "the books" and seems like I downloaded the frequency analyzer, but haven't tried it yet (just played with the Chadni modes until my wife confiscated her pepper mill). Question: is it possible to identify potential wolf notes simply by inspection of the frequency plots? Getting ready to put bridges on two classicals now, so maybe I'll play with them a bit before (or after?) I string them up. Hope I'm not getting us off the putty thread which seems reasonable to me, but my ear my not be good enough to appreciate the difference.
Author:  Alan Carruth [ Fri Feb 14, 2014 3:03 pm ]
Post subject:  Re: Improving Tone With Putty
Trevor Gore wrote:
"Some wolfs go and some stay or just relocate."
..and once in a while one moves in!

One of my customers had been using his guitar for about ten years before a buzz showed up: D on the third fret of the B string. Since it didn't show up at that pitch on any other string we figured it was fret buzz or back buzz or some such. Several hours of chasing the usual suspects didn't get it, though, and we were able to figure out that the string was not buzzing any place. Finally I recorded the note, and an FFT showed that the third, sixth and ninth partials had split peaks. We found a Chladni pattern on the top at around 880 that had an antinode centered where the B string crossed the saddle. A bit of mass moved the node line, stoping the problem, and removing some wood from the upper end of the upper tone bar effected a permanent fix. I still have no idea why that happened on a guitar that was ten years old.
Author:  Trevor Gore [ Fri Feb 14, 2014 7:10 pm ]
Post subject:  Re: Improving Tone With Putty
mkellyvrod wrote:
Question: is it possible to identify potential wolf notes simply by inspection of the frequency plots?

High, isolated peaks in the frequency response plot, where the peaks are centered on scale tones, are candidates for wolf notes. They're hard to pick before you put the bridge on, because doing that moves all the amplitudes and frequencies. So you generally hear the problem first, then confirm that it's to do with a body resonance (rather than, say, a bad fret) using VA.
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