Official Luthiers Forum!

I see that Al Carruth is one of the seminar speakers at this year's ASIA symposium. Al, What ya gonna talk about?
Are you bringing any "experimantal" instrument? Double top?

Word travels fast!

I volonteered to do a workshop on 'Measurement Techniques for Acoustic Quality Control'(I just figured out what to call it). I'm hoping Rick can find somebody who has more experience than I do at deflection measurements for wood testing to talk about them. I've done some stiffness and damping testing using the signal generator, and can show how that works. Maybe we can get into some of the stuff that Dave Hurd talked about in his book on assembled instruments. There's the whole 'glitter pattern' dog and pony show, both on 'free' plates and assembled instruments. I'd also like to talk a bit about 'impulse spectra' and other sound measurement techniques. Offhand I'd say we could keep this one going all weekend, particularly if there are some other folks who can chime in with their own areas of expertise.

A lot of this is stuff I've been doing for some time, and find useful. However, I must say that a big part of my motivation is the review that Evan Davis gave of Dave's book. Perhaps Evan was right in some sense, and Dave's measurements weren't very precise. To me that's almost beside the point: even farly crude measurements can be better than no measurements, and it seemed to me that a big part of Dave's motivation in writing the book was to show people how easy it is to get useful information on the instruments as you work on them. Certainly there are pitfalls, and you do assuredly have to be careful not to read too much into the data you get, but properly used it can be quite handy.

So, any volonteers to help out?

I don't have Dave's book yet so I can't comment on that. I don't think Evan's critisism is on the precision of Dave's measurements but rather that the theoretical models he is using do not reflect the physical realities of the instrument sound board.

I like your approach to science and lutherie. It think of it in terms of a gross catagorization. ie: Instruments that have the following glitter pattern tend to fall into the "sounds good" bin more often than those that don't. If an instrument has these "bumps" on its impulse spectra, it falls into the "sounds good" bin. If the bumps are small or narrow or whatever, they usually don't.

This level of granularity is all that is needed to make the technique useful. From reading David Hurd's website, I get the impression that what he describes could also be useful in the same way. If I get this much deflection in the top or a brace, I get a better sounding instrument. Too stiff or too floppy and it doesn't sound so good.

As to why these corrolations exist, that is phase two of the process.