Gore/Gilet/ Concepts & Falcate Bracing in a Uke Build

[charangohabsburg]

The added weight may, of course, make the instrument way too heavy for general acceptance - [...]

I disagree with the general acceptance. A good ukulele should be heavy!
I'm just trying to defend those heavy buggers ( = charangos) I'm dealing with... they sound way louder than any ukulele! (But they are not ukuleles).

Once you have the bridge on it may be interesting for you to compare the spectrogram of this falcate braced uke with the spectrograms you might take from some former builds (if you still have access to them). For me it will be interesting to read you opinion about such a comparison. I really appreciate your effort and would like to thank you here for sharing your experiment!

[Nick]

I know nothing of this frequency measuring & magic fairy dust stuff.......yet, but your spectrum looks like the Uke has a good bass reponse at this stage, am I reading that right?
And the Magic fairy dust at 521Hz makes quite an arse of itself! Great stuff Craig, keep it coming .

[Clancy]

It's hard to get my 8yr old son's attention with anything these days.
But when I showed him the video of the herbs 'dancing' on the uke, he said "Cooool. Where do you get those dancing herbs?"

[kiwigeo]

That back is definitely live

[Clancy]

...but your spectrum looks like the Uke has a good bass reponse at this stage, am I reading that right?

Umm, yeeeaaah, naaaah, sort offfff, not really, hmmmm.
I'm going to get myself tied up in knots here, but I guess it's a good opportunity to see if I really did understand the weekend's presentations.

The 2 high spikes at the lower end of the frequency spectrum are the coupled air resonance and the coupled top resonance.
These are 2 of the natural resonance frequencies of these components in this particular instrument (and in this case, the 2 strongest).
Although the main monopole mode, the first picture where the whole top appears to move as one, is located at a low "response frequency" and therefore appears to act as a "bass sound generator", it doesn't necessarily hold that a large monopole response equates to a good bass response.
The peaks are where the energy of the strings is easily transferred into motion, like an energy sink hole.

So, although it is desirable to have these natural frequency response peaks AWAY from actual note frequencies (because the energy is quickly sucked in and used), the region around which the peaks of the natural frequencies occur does give an indication of the characteristic behaviour of the top - both in general mechanical movement and the fact that the resonant peaks will have an effect on local frequencies around it and on other resonant frquencies.
So there are desirable locations to try to place the main resonant frequencies.
The book's authors kindly give suggested values for guitars,.
This uke will give a 'datum' for future uke efforts.

Just to confuse you further, the height of the peaks is relative to what your tap hammer is made of, and how hard you hit it!
The bandwidth of the peak tells you more about the resonant frequency than the amplitude does (I think).
For bass response, maybe the Monopole Mobility test is a better singular indicator as it measures the physical movement capability of the top rather than the frequency at which it naturally vibrates.

[Trevor Gore]

That's pretty right Craig. It's hard to explain how it all works without writing a book!

Just to confuse you further, the height of the peaks is relative to what your tap hammer is made of, and how hard you hit it!

...and where you place the mic.

These were all uncontrolled taps and I wasn't worrying about where the mic was, so having the first peak as the highest might just be an artefact of the mic placement. Probably best just to tap a lot of ukes first to get an idea of what's going on, then zero in on a more consistent data acquisition process. The peak heights, however, are always going to be only roughly comparative unless you go to a lot more trouble (anechoic chambers or piezo hammers and accelerometers, etc.). To me, with guitars, what's most important is having the frequencies of the peaks in the right places. The peak frequencies stay reliably the same practically irrespective of how you collect the data.

How this sort of data is used depends on what people value in the sound of a uke (of which there are many sizes and many uses) and I can't really offer detailed help with that until a target sound is defined (of which there may be many, and much contention!) But at least you get to chose and can target what you prefer with a good chance of hitting it.

[Dominic]

I know nothing of this frequency measuring & magic fairy dust stuff.......yet, but your spectrum looks like the Uke has a good bass reponse at this stage, am I reading that right?
And the Magic fairy dust at 521Hz makes quite an arse of itself! Great stuff Craig, keep it coming .

Nick, no magic, or fairy dust in sight. It is all grounded on the physical nature of stuff. This stuff obeys the laws of physics.

We'll leave any talk of magic to McPherson guitars and his sound channelling braces.

Dom

[Nick]

We'll leave any talk of magic to McPherson guitars and his sound channelling braces.

Dom

And thanks for the run down on what I'm seeing Craig.It's all a bit of the unknown for me just at the moment but when I get some "free" time to actually sit down & read Gerrard & Trevor's books I may get someway to working out what you just said

[J.F. Custom]

Hey Craig.

Thanks for the update and detailed info.

Those Chladni patterns are looking very well defined for the different modes, particularly say the T(2,1) - more so than I imagined a Uke may display. Goes to show what Trevor said "...showed every indication of operating just as I would expect a small guitar to operate. Funny, that."

Just one question though - this is a concert instrument or a tenor? You had said a Concert ~15" scale.

I ask though, as looking through what little cumulative data is available on ukes thus far, I note that :

the frequencies of T(1,1)1 @ 195Hz is the given value of the coupled air (Hemholtz) of a Tenor size instrument, as listed by David Hurd. A Concert he suggests is more in the range of 225Hz.

also the main coupled top monopole of T(1,1)2 @ 361Hz happens to be where Jeff High mentioned his Tenor top was also pitched. I don't recall David Hurd giving any details on his T(1,1)2 top monopole results.

So I am curious if this is a typo in that you are in fact building a Tenor; or if this is just where these happen to have fallen for this particular concert instrument? Interesting if so, that the numbers can vary so much - particularly T(1,1)1. If it is a Concert, what plan are you working to? Perhaps it has deeper sides and overall volume creating the lower frequency air resonance?

Anyway, great work. I'm looking forward to further updates and also to adding to the information pool in due time.

Jeremy.

[Clancy]

Thanks Jeremy, it's great getting this exchange of information.
That's why I started the thread!

No typo mate.
Pretty much bog standard Scott Antes Concert uke shape, 280mm body length, 192mm lower bout width, 15" back radius, 68mm deep at tail, 61 mm deep at head, 54mm diameter sound hole.

And just to re-confirm, the tap tested frequency response and the chladni patterns matched each other.

[J.F. Custom]

Thanks Craig.

Interesting indeed. Far more time and data is required to garner any sense of all this!

I'm hoping Allen, being a rather prolific Uke builder, will chime in with some figures/frequency charts at some point. Be good for further reference to collate some numbers together. As far as I know though, I don't think he has the books so he may not be overly interested in this side of things build wise as yet.

Perhaps there are other uke builders who might do some VA sonic signatures to share...

Look forward to your updates.

Jeremy.

[Clancy]

Jeremy, I've done the neck for this uke but the main thing I want to do is get the bridge on & tap test again.
There's some personal stuff going on at the moment that's stopping me from building, but I have been scratching around for some suitable bridge material.
Nothing that's light weight & stiff looks good with the gidgee binding & desert oak fingerboard.
Then today I came across some extra little pieces of brazilian rosewood that someone once gave me....
Hmmm, they're about 3.5mm thick and I only need around 80x20mm, so a composite with cf would give a light & stiff bridge that'll look right too.
Thanks again to that generous benefactor.

[Clancy]

I got the uke strung up with D'Addario J53's last sunday.
Thought I'd give you an update.

The bridge is 75-80 x 21.5 x 7mm and weighs 5.9g
The bone saddle weighs 3.1g, but at 4mm thicker is 1mm more than planned (thanks to using a new router with an old jig )

Here's the frequency spectrum

Falcate Cuke Complete FS 318.jpg (83.78 KiB) Viewed 25648 times

The T(1,1)2 has moved from 361 to 318hz - (Eb4 + 40c)
Nicely placed

You would have noticed that the T(1,1)1, previosly reported as 196, is bang on G3.
After much checking, tapping & zooming, I have concluded that it is actually 194.5
I didn't want to change this until I had the uke strung, hoping to be able to hear the difference after changing this resonant frequency.
Thanks to an errant dremel, my 54mm soundhole diameter is 2mm wider than the plan.
(I need a decent soundhole/rosette cutting tool. Hint. Hint.)
So I added some 1mm thick purfling to the soundhole.

Falcate Cuke Complete with hole purf 318.jpg (86.66 KiB) Viewed 25648 times

The T(1,1)1 is now 191.5Hz (G3 - 40c)
Much better (so stick to the plan!)

So could I hear a difference??
Umm.
Nup.
Sorry.

Next test - bridge rotation.
I had high hopes for having this in the 2Deg region, going by the trusty 'eyeball test'.
After performing actual measurements with real measuring thingies, I can report that it actually has exactly 1 degree of rotation.

So, that just leaves the final test.
How does it sound?

While it's not the loudest uke I've made, but it's far from being a whisperer.
Nor is it klunky.
Nor is it like a little guitar.
Strangely, it sounds just like a uke. Weird eh!

I'll definately get a sound sample up for you all.
And some pics just to complete the picture.

My Conclusion?
It's a good datum for future efforts.
And that's all I was really after

Now go forth and build and let me know what you find out.
GO!

[Clancy]

Oh, and someone who tried it out has asked for one, so it's already creating sales.
Noice one.

[Trevor Gore]

Oh, and someone who tried it out has asked for one, so it's already creating sales.
Noice one.

Noice one indeed!

Well done Craig, and thanks for posting this.

[J.F. Custom]

Great Craig!

Thanks for the update and congrats on finishing it off, not to mention a sale to boot. Got to be happy with that result.

Good to get some idea of the effect on the top main monopole, of the bridge on this little instrument - 43hz in this particular case. Did you try any weight adjustments in the sides to see what effect, if any notable, it delivered?

Thanks for going to the effort of not only creating this instrument and braving the onslaught of underminers, but documenting the results for anyone interested to see. It's been appreciated by me at least and I know I'll be referring to some of these figures when I get started on one too.

I certainly look forward to those promised pictures and sounds to complete the build log.

Cheers mate,

Jeremy.

[Clancy]

Thanks guys.

Haven't tried to fit any weights in yet Jeremy, will report when I do.
That's not to say that I haven't been mulling over the results so far.
It may be that a 1 degree of bridge rotation is more realistic on such a little, low tension instrument.
However, I have been thinking of how to go about achieving 2 degrees.
The main falcate braces are already so low that I can't see how you could lower them further & still achive structural integrity.
So that leaves the secondary falcates.
Removing them, as you suggested earlier, should allow greater rotational mobility - but at a cost to structure as I don't use a lower transverse brace, not too mention loss of control of cross grain stiffness.
Hmmm.

I also promised a sound sample.
I've been practising my chops all day....this is the best I can do.
To anyone who actually listens to these - My Apologies.
Recorded directly through the inbuilt laptop mic to the standard sound-recorder in Windows 7 Accessories.
Converted from wma to mp3 - no other alterations or additions.

The Pink Plucker.mp3

(741.13 KiB) Downloaded 826 times

No Lessons No Tune.mp3

(682.13 KiB) Downloaded 752 times

[charangohabsburg]

Hey Craig, that sounds like a uke, just as you told us. I still can't believe it!
Oh well, to be true... I'd like to say that is sounds like a nice sounding uke!

If the high tech recording and my about the same level high end sound reproducing onboard equipment don't cheat too much I'd be inclined to say that the sound is a bit on the nasal and "plonky" side, a sound that some uke players really appreciate while others don't like it so much. Without wanting to judge this matter of taste I believe that this kind of sound can often be found on relatively sturdy built ukes, and maybe (pure conjecture of mine) it has to do with the bridge rotation you mentioned. I am by no means an expert in compound materials techniques and CF, but I imagine that if you made even shallower braces this would not endanger the top's integrity because CF is such a stiff material. On the other hand, I think that one should not underestimate the top's strength by itself (without the braces). In my opinion you reach the optimum thinness of a top when after a few years the (fan-) bracing is getting evident when looking at the reflections of the top. This is maybe not very beautiful but it shows that you are relatively close to the minimum thickness before the top eventually would collapse.

[Allen]

Thanks for posting those sound clips Craig.

It does sound very "Ukey". Not guitar like to my ear. Does sound a bit tight to me but it's really hard to make valid comments about tone, projection etc. sitting at a computer on the other side of the country.

I would suggest to get it in the hands of some really good players and ask for unbiased assessment. I'm lucky in that I have one of the best ukulele players in the country living near me and I get an assessment on each instrument I build. It's helped me immensely on all kinds of things, including the ever so important neck shape and playability issues that accomplished muso's are looking for. Something that is really rare in a factory built instrument.

[jeffhigh]

Thanks guys.

Haven't tried to fit any weights in yet Jeremy, will report when I do.
That's not to say that I haven't been mulling over the results so far.
It may be that a 1 degree of bridge rotation is more realistic on such a little, low tension instrument.
However, I have been thinking of how to go about achieving 2 degrees.
The main falcate braces are already so low that I can't see how you could lower them further & still achive structural integrity.
So that leaves the secondary falcates.
Removing them, as you suggested earlier, should allow greater rotational mobility - but at a cost to structure as I don't use a lower transverse brace, not too mention loss of control of cross grain stiffness.
Hmmm.

]

I would not get too hung up on the bridge rotation aspect.
You really can't control for this and for the main top frequency at the same time independantly
If you get the top to the desired frequency and the rotation is not excessive you are fine.
As Trevor said to me something like- you hear the top pitch but see the bridge rotation.

[Clancy]

Jeff, it's not that I'm hung up on bridge rotation.
It's more that, as Allen said, it the uke sounds a bit tight.
I may have landed the T(1,1)2 nicely between 2 notes, but is it between the right 2 notes.
If I loosened the top up a bit more, increasing overall top mobility as indicated by bridge rotation, the T(1,1)2 would drop and a better target frequency might be found.
I'm going to have to do this on the next one to actually find out, I was just musing on how to go about this.
I could do it by adjusting my target stiffness & making an even thinner top, but at 1.7mm with edge thinning, I reckon I'm already getting close to the limit of something I'd be willing to give to someone else.
And with a really stiff top it would already need to be thinner to meet the current design stiffness.
So I'm re-considering the bracing.
Which might be the right or wrong thing to do!
Whadya reckon?

It may be that, after only 1 week, the uke hasn't opened up itself yet.
Can that still happen with CF sandwiched braces or does it eliminate the possibility?
Any experience with this Trevor?

Oh, and this particular thread has really gone where I hoped - a thoughfull & useful exchange of ideas for all to use.
Thanks for participating guys.

[Allen]

I've only used the CF in a lattice, and from my experience, what you start with is what you've got a few years later.

At 1.7mm thick (this was a concert wasn't it?) you aren't too thin in my books. If I was to be using that much bracing I'd be going even down to 1.5mm. With the concerts we do for classes they are 1.7 - 1.8 with just a bridge patch. No other fan type bracing at all.

[Trevor Gore]

It may be that, after only 1 week, the uke hasn't opened up itself yet.
Can that still happen with CF sandwiched braces or does it eliminate the possibility?
Any experience with this Trevor?

The sound of guitars tends to change a bit over the first two weeks or so. After that, the tonality doesn't seem to change, but they do seem to get a bit louder.

In terms of what to try next I'd suggest the following:

1) Try to find a great reference uke and tap it out and measure the bridge rotation. That will give you a stake in the ground at least

2) I still think you can loose the bridge plate

3) I'd say that you could tighten the curve on the secondary falcates so that the the "spokes" more evenly divide the soundboard. This will reduce the longitudinal bending stiffness of the soundboard and give you a bit more bridge rotation.

4) After that, it'll be about dropping the height of the braces and thinning the top a little more until you find the sweet spot (i.e. the modal frequencies that work best)

[Tod Gilding]

Craig,
I Havnt done the math, Just Thinking , but what do you think would happen if you were to make the primary and intermediate falcate braces slightly tapered (pyramid) with a narrow flat top just wide enough to lay the CF tow onto, this would remove a little more mass,but maintain the brace height. sorry if thats a stupid suggestion, .....I'm only posting a thought

[DarwinStrings]

Just doing some catching up Graig, great thread and nice work. I also read the UU one, got a big grin out of that.

Jim