Falcate braced classical

[kiwigeo]

That's what the small diagonal tertiary brace in the lower bout is for...and is currently missing from your design. A couple of diagonal grained diamond cleats will do the job if you don't fancy a brace there.

Well f**k me I knew there was a reason this has been bugging me for so long. Thanks alot Trev......will whack in the missing brace.

[Tod Gilding]

That would be Nick's fault, giving you that Scotch

[kiwigeo]

Did you buy your allen bolts off the net? If I could get your source that'd be much appreciated.

Got a selection of different length M6 allen bolts off ebay: http://www.ebay.com/itm/M6-SOCKET-HEAD- ... 4517833426

[Tod Gilding]

Looks Like a life time supply Marty, I hope you got Black T nuts to match them

[kiwigeo]

Steady progress on the classical. Kerfed back linings glued in and back all braced up. Today I started getting familiar with the spectrum analysis software and did some runs on the free plate top and back as well as doing measurements on a couple of finished instruments. Didnt get time to do some measurements on the lute but will play around with same later on in the week.

[kiwigeo]

Spectrum from VA for the top (attached to sides but no back attached):

[Dominic]

Hi Martin, I would be interested to see if your spec graph with no back looks anything like the uncoupled top freq (with soundhole plugged) once the back is on? If so you (and we) could test your monopole mobility before closing it up and get a sense of braced top stiffness and responsivness. And perhaps we could still have a chance to rip off the carbon and re-shape the braces. Be good idea to do a proto-type like that and try to zone in on our build stiffness. One thing Trevor repeated at the course was that build quality has a material difference on final stiffness and that he consistently got stiffer tops responses than students using the same materials.
Anyway, good luck
Dom

[kiwigeo]

Got the back on yesterday and this afternoon had a play around with VA and managed to identify some of the main resonances as follows:

Helmholtz - T(1,1)1 - 94Hz
Main Top - T(1,1)2 - 204Hz
Coupled Back/top - T(1,1)3 - 262Hz

Two as yet unidentified peaks at 317, 349Hz

Long Dipole? - T(1,2) - 425Hz (Nice big peak).

Three as yet unidentified peaks at 488, 584 and 724Hz

Will put up a spectrum when Ive got data processed.

[kiwigeo]

VA Spectrum.

[kiwigeo]

A better plot from excel. Plot is of 5 runs each run taking 10 samples. Microphone was held about 50mm above bridge centre this time around:

[Dominic]

So Marty, what's your analysis? The bridge effect is ambiguous on a classical as we have discussed previously.
Dom

[kiwigeo]

So Marty, what's your analysis? The bridge effect is ambiguous on a classical as we have discussed previously.
Dom

My initial interpretation as follows. I've yet to confirm a few of the peaks with Chladni patterns:

T(1,1)1 at 94Hz (F#2)
T(1,1,)2 at 202Hz (G#3)
T(1,1)3 at 262Hz (C4)

Trevor states that best combinations for a classical for these three peaks are either 100/190/240 or 95/202/254Hz

My guitar appears to be fairly close to the second case above with T(1,1)3 a tad high to Trevor's target.

There are a number of peaks in the higher registers.....eg 317, 349 and 424Hz which I have yet to positively identify. There are also peaks in the 450 - 750Hz range which are of great interest.

The main top frequency is fairly good where it is but will change when bridge goes on. My aim at this stage will be to keep bridge as light as possible to minimise change to main top resonance frequency. The bridge will probably be Tassie Blackwood and a CF/wood sandwhich as per G and G's book.

Note I didn't take any meat out of the lower transverse brace on the back preferring to see what I got with no alteration made to this brace. The back (just over 2mm thick) is very lively during tap tests on the top.

If anybody feels like making comment please free to do so.

[Dominic]

Well the bridge mass will lower the top freq but the bridge also adds cross grain stiffness to a classical which can raise the top freq. It will be interesting to see how it comes out.
Cheers
Dom

[kiwigeo]

More progress. Got the back glued on and bindings and purfs done. The blackwood bindings were an absolute pain to bend......had a few breaks but managed to repair them with superglue and they don't show. Did a bit of chladni testing...the photo is the main air resonance at 92Hz. Guitar wasnt perfectly level so poppy seed has collected on bass side more than treble side.

[Kim]

Nice mitres Marty

Cheers

Kim

[kiwigeo]

Nice mitres Marty

Cheers

Kim

Yeah I got lucky there. I used Trevor and Gerard's method of doing the butt strip where the bindings get glued in and then the strip gets fitted rather than my usual method of fitting the butt strip first and then doing the bindings and purfs.

Next job is the bridge.

[Dominic]

Yes nice mitres. I was wondering how Trevor got such clean patterns in the book and we discovered the brush trick at the course. And I thought I needed a louder speaker but all I needed was a 99 cent brush and some basic artist skills to clean up straggling tea leaves.


Dom

[Trevor Gore]

Martin, are you sure that's the T(1,1)3 at 262Hz? A quick way to check is to tap the back (mic'ing the back) and you should see a high peak ~260Hz if it is the T(1,1)3. Otherwise, you could check it with poppy seeds on the back.

[kiwigeo]

Martin, are you sure that's the T(1,1)3 at 262Hz? A quick way to check is to tap the back (mic'ing the back) and you should see a high peak ~260Hz if it is the T(1,1)3. Otherwise, you could check it with poppy seeds on the back.

I'll check it out tomorrow. I haven't actually verified most of the peaks above the main top resonance with Chladni testing.

[kiwigeo]

Today I did some more tap tests and compiled results pre and post binding. Prior to binding I thinned the top around the edges of the lower bout as per G and G's book and this has resulted in following changes:

T(1,1)1 - lowered from 92 to 87.5Hz
T(1,1)2 - increased to 210. Peaks at 136, 155 and 178Hz increased in amplitude.
T(1,1)3 - decreased from 267 to 251hz. A tap test on back gave a peak at 272Hz. Need to confirm this is T(1,1)3 with Chladni test.

[charangohabsburg]

Very interesting chart Martin.
Did you do first the top binding or the back binding?

[kiwigeo]

Very interesting chart Martin.
Did you do first the top binding or the back binding?

I generally do the back binding first followed by top binding. No real reason I do it this way.....its just the way Ive always done it.

Note the "bound back" plot on the chart is the spectrum recorded by tapping on and micing the back (lower bout).

[Trevor Gore]

Martin, how are you doing your data gathering? (VA settings, type of mic etc.) There seems to be a lot of stuff going on that I don't normally see and I especially don't see the T(1,1)2 go up in frequency as the top is thinned around the periphery.

I normally glue the top and back on (which "seals" the box, bar the sound hole); get readings from a first set of taps, thin the top around the periphery and do more taps, which always produce a lower T(1,1)2, and when that is at target I cut the binding channels and bind etc. If you tap with the binding channels cut and no bindings, maybe with holes through to the kerfs, you can get all sorts of strange readings which can't be related to anything much.

[charangohabsburg]

Martin, actually the point of my question was to know which curve is for back and top binding.

Note the "bound back" plot on the chart is the spectrum recorded by tapping on and micing the back (lower bout).

Thanks. I think this is a pretty important detail.

[ernie]

Just wondering, trev , can you substitute englemann spruce for bracing on the falcate classical top?? also what species of bracing is being used for the back on this oz blackwood classical ?? thanks