Falcate braced classical

[kiwigeo]

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.

Trev,

VA settings are as per guidelines in your book and Doms notes. Im running a Shure mic through a preamp and into line input on my Mac. The mic is 50-60mm from bridge centre and Im tapping on the bridge. Recording with the mic 50-60mm from soundhole doesn't make much difference to the peaks....just a bit of variation in amplitude.

I didn't do any tap tests while thinning the the top periphery....went straight to doing the bindings. The plot in my last post shows data recorded before thinning of top and cutting of binding channels and data recorded after glue in of binding channels....the only hole is the soundhole.

Note that prior to binding there were some extra peaks between T(1,1)1 and T(1,1)2 peaks...these have increased in amplitude with the thinning of top periphery.

Tomorrow I plan to do some serious Chladni testing. need to warn the neighbour first so they dont report aliens next door to the local cops.

[kiwigeo]

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

Ernie, back bracing is Englemann spruce. You could use Engleman for the top bracing but its not as easy to bend as the King Billy Pine Ive used.

[kiwigeo]

A clearer plot of bound top with back data also presented.

[ernie]

Thanks martin , I have englemann, an just got some euro bracing. What is a good substitute for KBP, balsa??. Guesssing that KBP bends easily for falcate braces. . I live in the midwest, kansas city, and was wondering what would be a good substitiute for KBP. that could be easily acquired cheers ernie

[ernie]

I will try bending or laminating the englemann first.

[Clancy]

Ernie, myself (& others) have been bending sitka without any drama.

[kiwigeo]

Englemann will bend fine for primary falcate braces but when youre doing tight radius secondary braces Ive found it challenging. King Billy Pine just bends like butter and I find it alot easier to work with.

[Trevor Gore]

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

Ernie, just go for the stiffest, least dense stuff that you can bend. Some spruce just won't bend without crumpling no matter how you try, but other stuff of the same species will. So it's just a case of shuffling through your stock until you find something. Balsa will fail in shear, so don't use it on a steel string guitar. You could try Alaskan yellow cedar, but that might be as hard to find as KBP. In Aus. silver ash (not a true ash and not made of silver!) is a viable alternative, but you're not likely to see that in the USA either. The Young's modulus varies a fair bit between these different species, so it is worth compensating for that with the brace height (work to a common EI number).

[Trevor Gore]

VA settings are as per guidelines in your book and Doms notes. Im running a Shure mic through a preamp and into line input on my Mac. The mic is 50-60mm from bridge centre and Im tapping on the bridge. Recording with the mic 50-60mm from soundhole doesn't make much difference to the peaks....just a bit of variation in amplitude.

I didn't do any tap tests while thinning the the top periphery....went straight to doing the bindings. The plot in my last post shows data recorded before thinning of top and cutting of binding channels and data recorded after glue in of binding channels....the only hole is the soundhole.

Note that prior to binding there were some extra peaks between T(1,1)1 and T(1,1)2 peaks...these have increased in amplitude with the thinning of top periphery.

Tomorrow I plan to do some serious Chladni testing. need to warn the neighbour first so they dont report aliens next door to the local cops.

That sound's all good Martin, though I've not tried this stuff on a Mac. You have a lot of peaks between 140Hz and 240Hz which are unusual, so it'll be good to identify those when you get the Chladni's going.

Not sure if a Mac allows you to do this, but:

When you save the tap file you should get both a text file and a picture file of some sort. On Windows its a .wmf file. I don't think the forum software will allow a direct upload of a .wmf file, but you can convert it to a .jpg (for example) using IrfanView (for example). IrfanView is a free download for Windows (don't know about Mac) and is a simple picture editor/file format converter. I use it heaps. That should save you pumping stuff through a spreadsheet to get a decent looking plot, but if you want composite plots, you will still need to use a spreadsheet. Also, make sure you only capture one tap per buffer update when recording the data. This gives you much cleaner plots with less "grass".

Have fun!

[ernie]

thanks trev , will try experiments in bending starting with the lightest englemann spruce , which is cheap and readily available at most homeless depot stores, a usa chain store . Also have carpathian, sitka spruce , and yellow cedar. Will see what works ,have some old doug fir and western red cedar, and redwood. We have a local hdwood that bends readily black willow, and basswood or linden.

[kiwigeo]

Not sure if a Mac allows you to do this, but:

When you save the tap file you should get both a text file and a picture file of some sort. On Windows its a .wmf file. I don't think the forum software will allow a direct upload of a .wmf file, but you can convert it to a .jpg (for example) using IrfanView (for example). IrfanView is a free download for Windows (don't know about Mac) and is a simple picture editor/file format converter. I use it heaps. That should save you pumping stuff through a spreadsheet to get a decent looking plot, but if you want composite plots, you will still need to use a spreadsheet. Also, make sure you only capture one tap per buffer update when recording the data. This gives you much cleaner plots with less "grass".

Have fun!

Trev,

VA works fine on the Mac....Im running it via Windows 7 running on Parallels emulator software. Im actually surprised at how seamlessly Windows is running on top of my Mac OS.

I've been using a spreadsheet to average dB readings taken over 5 sample runs (10 second runs). The spreadsheet also allows easier simultaneous plotting of more than one spectrum.

Frequency of taps is probably a bit greater than the 2 second buffer update so will try slower tap rate and see if that make any difference.

Note also I have been doing the recording with the guitar standing on its end on the bench and mic hanging from the ceiling. I note that you actually hold the guitar in a normal playing position during your testing.

After having a closer look at the data on the spreadsheet plot I've repicked the T(1,1)2 main top peak at 205Hz which isn't much different from the frequency I picked it at prior to thinning top periphery.

The main thing that has happened is the "extra" peaks between 140 and 250Hz have become significantly amplified. What issues does this present for the sound of the instrument?

[Trevor Gore]

Note also I have been doing the recording with the guitar standing on its end on the bench and mic hanging from the ceiling. I note that you actually hold the guitar in a normal playing position during your testing.

Ah, that could explain things. You may well be measuring the response of the guitar coupled with the bench.

The main thing that has happened is the "extra" peaks between 140 and 250Hz have become significantly amplified. What issues does this present for the sound of the instrument?

Well, if they're real, more peaks is generally good. But it's hard to think of a mode/modes that will produce peaks like that. So at the moment I'm still thinking they are an artefact of the way you're collecting the data. Coupling with the bench top etc. can also stuff up Chladni patterns. Working on a concrete floor will usually fix that, but it's hard on the knees!

[kiwigeo]

Note also I have been doing the recording with the guitar standing on its end on the bench and mic hanging from the ceiling. I note that you actually hold the guitar in a normal playing position during your testing.

Ah, that could explain things. You may well be measuring the response of the guitar coupled with the bench.

The main thing that has happened is the "extra" peaks between 140 and 250Hz have become significantly amplified. What issues does this present for the sound of the instrument?

Well, if they're real, more peaks is generally good. But it's hard to think of a mode/modes that will produce peaks like that. So at the moment I'm still thinking they are an artefact of the way you're collecting the data. Coupling with the bench top etc. can also stuff up Chladni patterns. Working on a concrete floor will usually fix that, but it's hard on the knees!

Im currently in the workshop doing some extensive Chladni testing. Will take another hour or two to finish the testing and another few hours to collate the data and present same. Ill post up results tonight or tomorrow.

During tap testing the guitar was sitting on a carpet pad on top of the bench. Ill try sitting the guitar on a concrete tile or maybe I could hang the guitar from the ceiling and then it wont be coupled to anything.

Man I thought alcohol and chicks were addictive.....theyre nothing compared to this Gore and Gilet stuff.

[Trevor Gore]

Martin, just hold the guitar as you would if about to play it. No need to make things any more complicated. Tap with a small rubber tapper (a bit of eraser or super-ball on the end of a thin stick). My current tapper is a piece of super-ball on the end of a bamboo skewer. The natural frequency of the tapper is <5Hz, i.e. miles from anything you're likely to want to measure.

[kiwigeo]

For chaldni testing Ive had the guitar sitting in the carrier that I use on my binding channel cutting jig. This means the back is free to vibrate when doing top patterns and vice versa when doing the back.

[jeffhigh]

Man I thought alcohol and chicks were addictive.....theyre nothing compared to this Gore and Gilet stuff.

I dunno Martin, I'm sitting here with a glass of wine , looking at pictures of falcates and nothing is coming up so to speak
Am I doing something wrong or have I just reached the age where a man needs some chemical assistance?

Do I need to take Trevor out for dinner first or send him chocolates?

[Trevor Gore]

For chaldni testing Ive had the guitar sitting in the carrier that I use on my binding channel cutting jig. This means the back is free to vibrate when doing top patterns and vice versa when doing the back.

... and possibly means the carriage is acting as side mass...

Foam wedges seem to work OK.

[kiwigeo]

Do I need to take Trevor out for dinner first or send him chocolates?

I wonder what sort of tap test a chocolate would give??

[Trevor Gore]

I dunno Martin, I'm sitting here with a glass of wine , looking at pictures of falcates and nothing is coming up so to speak
Am I doing something wrong or have I just reached the age where a man needs some chemical assistance?

Do I need to take Trevor out for dinner first or send him chocolates?

Jeff, I'm getting seriously worried about you. I already know you have a bed in your workshop. Not sure that I'd be visiting any time soon...

[jeffhigh]

Trev, Trev, I'm heartbroken by this rejection......

[Trevor Gore]

I wonder what sort of tap test a chocolate would give??

Sounds like it's time to be tapping into a barrel of that Coonawarra that your compatriots are so adept at producing.

[Trevor Gore]

Trev, Trev, I'm heartbroken by this rejection......

You'll get over it. Try some of that red medicine that comes from down Martin's way.

[kiwigeo]

Ok Ive got a bit of tidying up work to do tomorrow with the Chladni testing and I need to re-do tap tests do make sure my testing method hasnt produced alot of the extra peaks. Here is a summary of todays top Chladni tests:

87.5Hz -strong monopole. T(1,1)1
136Hz - strong monopole.
157 and 178Hz - moderate monopoles.
205Hz - Strong monopole. Main Top Resonance. T(1,1)2
220Hz - Moderate monopole. Only other monopole present above 205Hz.
253Hz - Strong Cross-Dipole. This was my candidate for coupled back resonance but if so it should be a monopole?
279Hz - Weak Cross-Dipole. Closest top peak to peak at 272Hz recorded when tapping/micing back.
311Hz - Strong Long Dipole. The only long dipole I could see (tested up to 1000Hz)
385 and 409Hz - Strong Cross-tripoles.
445 and 567Hz - Strong Cross-Dipole.
592Hz - Strong Cross-Dipole

Nailing down the back coupled T(1,1)3 peak is a mystery. It should be a monopole but the only peaks close to the 272Hz back peak are cross dipoles at 253 and 279Hz. Can T(1,1)3 possibly ever be a cross dipole mode peak????

[jeffhigh]

Just a few comments, I don't know what all of these extra peaks are but..
You don't have the bridge on yet do you ? that will make a difference.
Your main falcate braces are quite widely spaced. but you have a bridge plate so that is probably compensating.
Perhaps the back is too stiff without scalloping of the lower bout brace as yet, to couple with the top and show a T(1,1)3 response.

[kiwigeo]

Just a few comments, I don't know what all of these extra peaks are but..
You don't have the bridge on yet do you ? that will make a difference.
Your main falcate braces are quite widely spaced. but you have a bridge plate so that is probably compensating.
Perhaps the back is too stiff without scalloping of the lower bout brace as yet, to couple with the top and show a T(1,1)3 response.

Jeff,

Thanks for the comments.

No bridge isn't on. Haven't even started making one yet. The aim will be to keep the bridge as light as possible.
Yes the primary and secondary braces are spaced wider than on the plans.
Not sure if back is too stiff......when I tap and do chladni testing on the top the back certainly feels very active. Today I Chladni tested all back tap test peaks. The lower bout is active at 270, 490, 520Hz while the upper bout is active at 445, 870 and 890Hz. Moderate to weak activity was detected at numerous other frequencies also. Playing with the lower transverse brace stiffness is certainly an option but Im wary of same changing main top resonance which is currently where I want it.