tap tap tap

Since the time I started building ukuleles I have tried to unravel the mystery of tuning the top and back plates of a ukulele. During my last build it dawned on me that like a string, pitch is determined by both mass and tension. Tap tuning has always dealt with tension by shaving down bracing to lower the pitch of a plate. So, the instrument I was building taped about 75 cents apart after gluing on the top and back, and shaving braces would only bring them closer together before beginning to achieve the recommended 1 – 1 ½ step separation. That would have weakened the braces more than I wanted. So I added mass by attaching ebony bars to the outside of the back using high-tack double stick tape, and was able to precisely tune it by adjusting the length of the bars. Ah-ha I though, I can finally do an experiment that will prove how well tap tuning works. Then I played the ukulele and it didn’t help – it sounded the same with or without the bars. I was already happy with the sound and the F# wolf note didn’t bark all that loud anyway. The one thing that never made sense to me about tap tuning is that there is no way for the box not to have its own frequency, and when you play a note anywhere close to that frequency (no matter what it is), the string will jump from the fundamental partial to the second and loose volume and sustain. Does anybody know how or have a method to make tap tuning work?

Im not sure i would use the word tension. I think you mean stiffness. Tension only comes about when strings are on but strings dont effect the top and back pitch of the box when you are using a tone generator to find out the resonate frequencies of the top and back.

One way is to keep the back thick. Take a reading, then sand the back down widening the separation towards your target pitches.

ALso, the top and back numbers get thrown out when you glue a bridge on. The mass of the bridge can be used to your advantage.

FROM MEMORY (and i have a bad memory) 3 grams of weight equals 1 Hz drop in pitch when dealing with the bridge.

All this stuff can be found in this book written by Trevor Gore and Gerard Gilet (I used to work at Gilet Guitars in Sydney, Australia)

http://www.giletguitars.com.au/book.shtml

Thanks for your response. Yup, the string analogy wasn’t such a good one I do mean stiffness. I understand the concept of removing material to affect stiffness, the need to consider the bridge, and the role strings play. When I assembled my uke, I was 25c off and would have had to remove enough material to change the pitch by almost a full octave to meet my target. So, just as an experiment, I added material to the back (taped-on ebony bars) after the uke was done to make the pitch higher, not lower. Through trial and error, I was able to tune the back at exactly one, and then one and one half steps apart from the top by trimming the length of the bars – and it didn’t improve the sound of what was already a great sounding ukulele.

One problem I see with removing (or adding) material to change the pitch is that you compromise the optimum thickness of a material for its given function by doing so. Why carefully thickness-sand or carve a brace for the very best flexibility when you’re going to then remove more material to achieve a certain pitch?

Does the bridge weight/pitch formula apply to all sizes of sound boards?

I’ve read some of Trevor’s stuff, and all of the now seemingly debunked Siminoff work on tuning. The plate tuning part of information I’ve read seems to distilled down to just getting the assembled plates to be one step (Gore) or one and a half steps apart (Siminoff). Other than all the other factors that come together to affect sound, is that all that needs to be known about plate tuning?

I also mentioned “wolf” notes and was wondering how much of plate tuning is aimed at minimizing them. What do you know about dealing with them?

For me, I'm better off working through what Dr. David Hurd calls "Compliance Testing" than worrying about tap tuning. I did use Mr. Siminoff's methods when I built some F-5 mandos and they sounded good but with ukes I get much better and consistent results with the compliance testing. You have to establish a bench mark tho. I've checked the tonal difference between the uke tops and bottoms and there is a difference but I don't have my Conn Strobotuner anymore so I can't say how much difference there really is. I'm not completely convinced that the tonal diff between the top and bottom means that much but.....I've been wrong a whole lot of times before
You can find out about Dr. Hurds Compliance testing here ukuleles.com

Thanks, Terry. Good to hear that tap tuning might not be the end-all. I'm familiar with Hurd's work, but get lost in some of his calculations. I do get it when it comes to "compliance" and have worked to establish the benchmarks you speak of over the years, and they do seem to work. One thing I do is base the bridge position on my fan bracing length rather than where it ends up with 12th or 14th fret neck/body positioning. I also stiffen the waist brace to a point where unwanted sound hole area deflection can be controlled.

The trouble with tap tuning books without science is it is a bit like describing colour to a blind person.

Tap tuning works but only after many instruments and a pattern you can remember for what a good tap is. Doing a class with good and bad tapping tops would be a way to spead it up but other wise your trying to mix yellow and red pigment into a canary yellow colour without without ever having seen a canary.

another way is to stick "blue tak" ("putty" in america?) to the top to add weight and stop wolf notes-
You dont have to really aim for a perfect separation, you just dont want the top resonating WITH the back or ON ANY scale note- so get the top between eg G and G#, never on either.

http://www.amazon.com/Blu-Tack-Reus...adhesive&pebp=1422819136864&peasin=B001FGLX72

I think the bridge gram thing applies to ukes too- shoot trevor a quick email to find out (let us all know!)- wish him a happy 60th birthday, which was a few days ago.

Here are my seven ways to make a great sounding top:

1.Select the best quality perfectly ¼ sawn wood.

2.Use wood with a good even grain count (no less than about 20/inch). This is
less important than using perfectly ¼ sawn woods.

3.Determine the thickness of your plate based on species and individual wood
characteristics. E.g. cedar and redwood need to be thicker than spruce to have
the same stiffness. (I used to deflection test my plates with a dial indicator,
but can now determine stiffness from experience without testing).

4.Determine your bracing thickness based on string load. (I used to use dial
indicators for this too, but now rely on a sense that tells me how much
resistance there will be to string load.

5.Position the bridge over the bracing based on where it works best rather than
where it falls after setting the neck/body joint at the 12th or 14th fret.

6.Stiffen the waist brace (and sound hole area) so that they resist bridge
torque and allow the bracing under the bridge to do its job.

7.Change pitch by increasing the size of the soundboard rather than carving and
sanding

I build two models of tenor ukuleles that have larger than average sound boards,
and I’m gravitating toward building more of them because they sound noticeably
better than smaller body ukes. The tops of these ukes tap between F and F#
without fail if I do all the things listed above. I prefer F - F#, because
anything closer to open notes (like G – G#) will make the wolves more
noticeable.

I’m beginning to believe that there is more than one path to a great sounding
instrument. As Beau has indicated, experience will determine where it leads.
And, as Terry said: “I've been wrong before”.

I think that there is definitely more than one path to achieve a great sounding instrument and that the process is justified by the end result, a great sounding instrument. I'm sure that there is no exactly right way.
I find it hilarious that here I am schooling you on compliance testing and you know way more that I do about the subject and have much more experience than I! I've been looking for that "egg on face" emocon.
I'm finally getting that feel for the top and have been using the compliance less but I still do a final check with the dial just to make sure.
One thing I really like about the compliance/flex testing is that my instruments have similar sound characteristics even with the different coloring that different woods bring. But like I said, I'm finally developing that feel.
Thanks for a thought provoking thread

terry

I'm still a little fuzzy on why tuning the back plate on my ukulele didn't change the sound, I did pick up a few things in Beau's comments, and that helps -thanks.