SS 14 fret falcate

[Ken Lewis]

Hi all
I recently buffed and glued the bridge on a 14 fret SS. Lutz top with Ovangkol B&S . I followed the Books' methods for bracing and thicknessing top and back as well as laminated maple top linings and live back. Top thickness 2.8 mm, back thickness 2.4 mm.
Before installing bridge the the spectrum freqs. were just above 98hz for the main air, 193hz coupled top and around 230hz for the coupled back with minimal scalloping on the main rear brace. After stringing up the spectrum plot is as below with main back brace shaved to around 10mm for about 110mm. I tried adding some weight to sides and back with magnets and washers, couple hundred grams or less, with negligible results. No provision for side mass loading as the guitar seemed heavy for me already at 2.5kg. Since the main air and top freqs. are favorably placed at 95ish and 180. I'm curious as well as cautious as to how to procede with further freq. trimming. The guitar sounds as good as any others I have built but probably not better. I would like better. This was my first based on the books. However it has only been strung up a couple of days and setup is not yet complete, very close though, out of the gate.
Also, the fact that the coupled back freq. doesn't seem to want to readily move for me means what? that the back is not as live as we would like it? perhaps.
Trevor, btw. awesome books.
Ken

[Trevor Gore]

I tried adding some weight to sides and back with magnets and washers, couple hundred grams or less, with negligible results. No provision for side mass loading as the guitar seemed heavy for me already at 2.5kg.

Interesting! I've not built with Ovangol, but that seems like a heavy guitar. Mine come out at about that for a 000 size (the drawing in the book) with weights added, EIR B&S. They clock in around 2kgs without the added mass. Ovangol is in the same density range as EIR, but stiffer, if the Wood Database sample is representative.

Unfortunately, adding mass using magnets won't get you anywhere. The added mass needs to be seriously attached, which means fully torqued M6 socket head cap screws when I put the weights in. If there is any chance of the weights not moving with the sides they don't work.

Try taking a tap response of the back and check if your 231Hz peak actually is the T(1,1)3. Did you measure the monopole mobility?

[kiwigeo]

Ken do you have the tap testing data from the raw Lutz top set? What sort of density and stiffness values did you calculate?

[Ken Lewis]

Hello Martin
Here is my data for the half plates for the lutz top
L 563mm
W 210mm
t 5.3mm
mass 243g
fl 99.4hz
fc 174hz
flc 69.25hz
By all means please run the numbers as a check for me. I came out at 2.8 mm
Oh! I used standard SS top numbers for f (75 I think)

Getting to Trevor's response I did some more tap testing and ran the numbers for monopole mobility. Bridge rotation is 1.7 degrees. Other guitars I've built came in closer to and just a little over 2 degrees. This one a little stiffer no doubt due to the CF. I came up with 24.5 s/kgx10^-3 for monopole mobility. I'll give the data so that you can double check for me.
Mass .448 kg (measured 1 lb.dumbell)
Deflection .0001016m (.004 in. measured)
Closed box frequency 170hz.
With a 2 lb. dumbell the deflection was doubled.
I've included three taps all with soundhole plugged. Trevor when you said to do a back tap test I assume you meant to tap back with soundhole plugged, I am not sure. The middle plot labeled back-back closed is the one where I did this with 230 hz showing up. Perhaps you could clarify this for me. The guitar sounds fine, I just want it to be all that it can be, and learn a few things in the process. Maybe 230 is ok for the back, just not sure?, maybe shave more off back brace but am aware that might mean moving main air and coupled top freqs. to less desirable locations.
Thanks for your help.
Ken

[Trevor Gore]

I came up with 24.5 s/kgx10^-3 for monopole mobility. I'll give the data so that you can double check for me.

The maths checks out OK, Ken. Certainly pretty high!

Trevor when you said to do a back tap test I assume you meant to tap back with soundhole plugged, I am not sure.

It doesn't really matter, Ken for the purpose of this exercise. I just wanted to be sure that what you were seeing was the T(1,1)3. You're showing a peak at 230Hz on your back/back plot, which is probably the back monopole, though normally the back main monopole is the tallest peak in the picture. You seem to have something going on at ~300Hz. Do you know what that is?

With a 180Hz T(1,1)2, having the T(1,1)3 at ~230Hz is fine. You could drop the T(1,1)3 a little if you wish to a 4 semitone separation (226Hz) though the difference in sound would be fairly subtle.

It seems like you've been making some nice guitars!

[Ken Lewis]

Trevor Gore wrote "You seem to have something going on at ~300Hz. Do you know what that is?"

Not sure at all, thinking it could be just ambient or system noise I recorded some taps using a recording software (Audition) whereby I could do a noise reduction thus eliminating anything other than sound from the tap. Checking the FFT's still there, seems to be more prevalent when tapping the back and with soundhole plugged as seen in the plots in my previous post.
With soundhole open T(1,1)2 T(1,1)1 T(1,1)3 have amplitudes in that order with the one at 300hz being lower than these.

Trevor Gore wrote "It seems like you've been making some nice guitars!"

Heh! Heh!, maybe some day someone will want one bad enough to buy one.
In the meantime it's not hard to give them away. You couldn't swing a cat around here without hitting a guitar player.
Again, Trevor thanks for the books and the help here.
Ken

[Woodsy23]

Trevor,

The question that this thread and the my own falcate SS build raise with me is:
Is it possible to have several similar guitars all with the same good "numbers" for resonant frequencies, monopole mobility, bridge rotation etc but with noticeably different performance acoustically? For example, have your students produced guitars with good "numbers" that don't sound as good as your exceptional guitars? If so, what could be the reasons and is there anything else that could be measured?

[Trevor Gore]

Interesting question.

It reminds me of the story about when the Japanese began to move up market in musical instrument making. The Japanese wanted to get into concert quality pianos, so they imported a Steinway and took it apart, measured every little piece and reversed engineered their Jeinway. So the story goes, it sounded nothing like a Steinway. So they reassembled the original Steinway parts, and that sounded nothing like a Steinway either; the moral of the story being that a complex musical instrument is a lot more than the sum of its parts.

So what defines the gap between a stack of parts and a Steinway? I don't know enough about pianos to answer that, but clearly, amongst other things the set up matters. In Build Section 4.11 I talk about craftsmanship in an attempt to explain some of the differences between my guitars and student guitars. But also Gerard's guitars sound like Gerard's guitars, whilst mine sound like mine. And we don't have a good explanation for the difference. Another thing that differs (and a lot of things contribute to it) is the damping across the sound spectrum of the constituent materials (sound spectral absorbance, for want of a better name) and the equivalent property of the finished guitar. Guitars put together with very closely fitting joints, fresh, smooth surfaces and the other stuff I mention in Section 4.11 will all impact on that.

The difference between really good guitars and truly great guitars lies somewhere in the rather murky world of setup, sound spectral absorbance and craftsmanship and likely some other things, none of which are easy to measure or to teach. About all I can say about "it" is that the more one builds, the better you get at "it". Usually. Even when you appear to be doing nothing different.

Best I can do, I'm afraid!

[Ken Lewis]

Well now, Late night is probably a poor time to run tests and hurredly post the results.
It wasn't even 'til a few days later that I realized that 24.5 x 10^-3s/kg was an unrealistic number for my monopole mobility. (after doing some more reading in the design book) I'm surprised no one was quick to point that out. you fellas are too nice I redid the deflection testing to see how I got the numbers. The short of it is that during the top deflection test I didn't have the guitar chocked up high enough leaving the back touching the bench giving me inaccurate results. I redid the deflection test, this time on a granite
bench with the guitar properly chocked and came up with a deflection of .0028". A thousand of an inch is a lot. My testing rig is similar to the one Jeff Highland posted in another thread. So the monopole mobility now is around 16.9 x 10^-3 s/kg,
still not too shabby. I know that the numbers alone aren't everything, just an indicator of the possible potential. After intonating, tweaking the action and a couple weeks playing in
I think it to be the nicest sounding guitar of the dozen or so I've built.
I also did some more tap testing, (again after rereading some more) this time more systematicly, paying close attention to where I was tapping. Trevor asked about the peak
at around 300hz in one of the plots, as to what it is. I'm thinking it is the cross dipole freq. because I can call it up to a high amplitude by tapping the bridge wing. I am not set up to
do Chladni testing so I haven't thought about this before. It's in the book though.
Time to go, it's getting late here again!
Ken

[Trevor Gore]

Thanks for the update, Ken. Good to hear it's all making sense and that the guitar sounds good.