Australian/New Zealand Luthiers Forum

I admit to somewhat of a lack of experience, as excel scared me off early on, but, today, I would never let a student do what needed to be a serious computation using it, and I would not attempt it myself. The discussions in this subforum alone are enough to point out why. You would need to go to pr...

Like a Northern version of a type 15! Very cool.

I know the feeling Trevor - someone asked me a question on what I remember was something like a truncation of this model back to 2 dof and I said I'd check it out - last March I think it was ... I've been making him wait almost as long as my most recent guitar customer

Well, I'm not a new member, but I don't get here enough. I've taken part in a few discussions about Trevor's book (mainly being a pain in the %#^ about a typo in the theory part of the 4-DOF model that I stand by). I have been too busy with my real job lately to keep up with luthin' and I apologize ...

I have to go in the fish glue defender column too. I use it for the entire guitar, and have had no immediate trouble after I learned not to over-clamp joints like bridges and fingerboards. Fish glue will keep moving for a long time under pressure and it is possible to starve joints. My guitars are l...

Thanks for keeping this going everyone, and sorry for not getting back. I took a holiday! Then there's all the other sh!t I've been having to deal with recently (nothing serious, just takes time). Anyway, there's about two days effort to go through all my workings again to check everything term by ...

I haven't gotten that far in applying the books yet, but I'm guessing that the block itself is another fabrication job like tail and head blocks. But they are mighty slim on information about what are convenient things to bolt to the blocks. Large washers would be my first guess, I think. (I misread...

Tod Gilding wrote:+1 what John hall said, I would love to build an Instrument with one of my Son's

I know - I waited until I was about 45 before I hung out with my dad and built a few furniture projects. He was only around to see my first guitar. My kids are still in their early 20's - no interest yet.

lapsteel-front.JPG Here's mine. Geometry is from the Supro plan obtained from Elderly. Tuners cost at least $10 US. Tele pickup assembly cost at least $15 (all the way from China, of course). Body is a piece of maple from the garage. fretboard is a piece of laminate with the fret positions gotten b...

I'm proud to be a propeller head, yup!

Dom, I'm curious about the mismatch in the air resonance peak after my change as well, given that the rest of the plot is really close to Trevor's. I want to spend some time checking on what parameters that peak is sensitive to - maybe something that isn't all that well constrained? (i.e., can I reg...

Jim, what do you think AII 2-38 to AII 2-43 should be? Hey Dom - I believe that it's the derivation of AII 2-38 to create AII 2-43. If you derive AII 2-38, we've both been getting F(+Kt.Kb.alphaab +...) instead of the F(-Kt.Kb.alphaab +...). A more complete explanation here: http://www.anzlf.com/vi...

But this IS the propeller head forum, isn't it? (Or at least the propeller head thread).

Dom, I got the same Dbar as the book, but different numerator in y_a. The step from AII 2-38 to AII 2-43 clearly has an error as printed, in the numerator.

Happy New Year everyone.

Jim

As for the math, the Wikipedia article on determinants is enough to go by. (I admittedly checked myself). I had a go at this & have to agree with you that I'm getting a positive value for the first term in in Equ AII 2-43 (ie., F(+Kt.Kb.alphaab +...). My solutions for AII 2-40 & 2-41 were the same ...

Steve - exactly the same as mine. As for the math, the Wikipedia article on determinants is enough to go by. (I admittedly checked myself). As for the change in amplitude of the peak, a lot of the peaks near resonance are based on dividing small numbers by small numbers, and can be really sensitive ...

To summarize, in hopes that someone is checking the math too: It's not the programming, it's that, if Equ. AII 2-38 is correct (which I think it is), then Equ. AII 2-43 and it's corresponding copy in the main text is wrong. And I suspect the error is purely a typo in the text rather than something t...

Greg, I forgot to add an explanation of the .(operator) construct. This indicates an element by element operation on an array where you are retaining the identity of each element. For example, the F./Dbar, where F is a scalar and Dbar is a vector, gives a vector with elements F/Dbar(1), F/Dbar(2), F...

Greg, The code got a little mangled by the upload as inline text - the forum software deleted all blanks inside comments or after major punctuations. I'd be glad to send a copy of the original to anyone who sends me an email address. The inline version would run but it's harder to read. Matlab uses ...

I couldn't find a file extension that the board would let me upload (what do you use for ASCII text files? Here is the code inline. Jim %-------------------------------------------------------------------------- % % gore_gillet_4dof.m % % Implements the 4 DOF model described in section 2.4.1 in Gore...

Here is the matlab .m file. Please let me know if you find any errors.

Jim

OK, here is what I get. First, two pictures. The first is the book example with the sign change I claimed above needs to be made. The second is what I get without the sign change (i.e., using the formula as given in the book.)

Thanks for your reply. Actually, the error in the printed solution is easy to see starting from the form AII 2-38. The numerator will be -F det ( the 3 by 3 matrix subdominant to this) which becomes -F ( -K_t K_b alpha_ab + D_s D_b alpha_at + 0 -alpha_at K_b^2 - 0 -alpha_ab alpha_bt D_s) which gives...

Merry Christmas to all from the U.S. East Coast. I have been trying to program up the various tools in the book in matlab (I know nothing about excel), and I had been stuck trying to reproduce Figure 2.4-4 with my code. I was getting very strange behavior at 100 Hz and below. I have rederived the so...