Official Luthiers Forum!

I know, it's been discussed a lot, but I have a specific question about the tap
tones I'm hearing on my current build.

After gluing all the braces and shaping them some, tapping produces a
grouping of pitches, all different but close together. If I move across the
bridge area tapping all the while, I get even more closely spaced but
different pitchs. I don't have a lot of experience with tap tuning and haven't
built enough acoustic guitars to tell if I'm going to get a good sound or a
poor sound out of this top. So, for those of you who regulary tap your tops
while building, does this one sound like it'll be good, or do I need to further
shape the braces? I plan on attaching the top to the sides and repeating the
tapping before I glue the back on. Just wondered what others of you hear
when you get a top that turns out good. Thanks!!

I never go for a specific pitch when I tap. I'm more or less looking for a
somewhat long sustaining musical tone. Now I know that is really hard to
even make sense of, but where I want this tone came from years of
experience. I also, just as much as tapping, use stiffness as an indicator.
This also can only be really acquired through experience.

Post a picture of your top with some thickness measurements and I bet
we can get ya real close so if nothing else it will sound good..maybe not
to it's full potential, but good.

On the other side of the coin there are plenty of people out there who
think tap tuning is total hogwash, and there are those who take a more
scientific approach and use glitter patterns, and frequency generators.
There are, for sure, a lot of ways to approach this, but if you supply some
pics and dimensions we can get ya close.

_________________
John Mayes
http://www.mayesluthier.com

Thanks, guys. Yes, my top is very lively and adequately stiff. When I did the
preliminary carving of the braces, I carved the braces on the bass side a bit
more with the idea that it should be slightly looser. I do get a nice ringing
without a single distinct pitch. I'll post some pics and dimensions later today
and see what you think. And I don't think tap tuning is hogwash at all. I
learned to make instruments from violin makers, and they are very serious
about the resonances of a top while carving it. Hours of tapping, carving,
flexing, more tapping, carving, etc. So I'm biased. I just don't have a lot of
experience with guitar tops. The DVD sounds like just what I need at this
stage. Thanks!

OK, here's the top:
2007-04-07_141328_6er_top.jpg">

Braces are 1/4" wide for the finger braces and lower face braces, 5/16"
for the X-braces and soundhole braces, and 1/2" for the upper face
braces. The soundhole braces will be butted up tightly to a mahogany
fingerboard support tongue extending out from the neck block. Bridge
plate and X-brace spider are African blackwood, about 1/8" thick. X-
braces are 3/4" high, the rest are about 1/2" high.

The top is Engelmann spruce and the braces are all Adirondack spruce. As
you can see, I've done some shaping of the braces already, but there's a
lot more to be done. If the braces are their final shape, they need sanding
and smoothing at the very least. The sound is lively and loud, but I'm
stymied by the situation that I don't know when to stop carving the braces
until I've gone too far...

Picture didn't post... trying again:

[IMG] http://i177.photobucket.com/albums/w224/crazytooguy/6ertop.j pg[/
IMG]

[IMG] http://i177.photobucket.com/albums/w224/crazytooguy/6ertop.j pg[/
IMG]

http://i177.photobucket.com/albums/w224/crazytooguy/6ertop.j pg

Copy and paste....

From the look of the top I'd say the lower face braces may need a bit
more of a triangular profile as it does not reduce stiffness much but it
lightens the top up. The brace size looks ok though. The x looks pretty
beefy in the center, but then looks like it tapers down quite a bit. I'd
leave them alone. The finger braces look a little big, but not much. More
so than anything I like to have the peak of my finger braces cloe to the X
than what you have, but that is not to say I'm right..I'm sure yours are just
fine. Of course all this is based on the assumption that the top was really
stiff to begin with.

All in all I think you could just leave it all along and be fine. How thick is
your bridge plate? How thick is your top?

_________________
John Mayes
http://www.mayesluthier.com

Pat-
If you can get your hands on a copy of

Kit Review: LMI's OM Guitar by John Calkin
AL#74 p.48

in the GAL publications, there is an interesting sidebar called 'Ferrari OM' on lighter bracing for a personal guitar.

Also, a good search in the archives (or a request for sample pics in a new thread- this could be a good resource for everybody) should get a bunch of pictures showing typical bracing sizes.

I'd say your pic (with 5/16 X, blackwood x cap rather than spruce, hefty transverse brace) would be toward the conservative/heavy end of the range, but not extreme at all.

You can't go far wrong with John Mayes 'stamp of approval'- he's seen a lot of guitars and can translate from bracing appearance to sound better than most of us.

Cheers

John

I'm not doing well with the picture posting. Thanks for the help!

Yes, I haven't shaped the lower face braces yet, and I was wondering how
light they should be. The top is pretty stiff - stiffer than other Engelmann
I've worked with and it's about 0.100" thick. I plan on thinning it slightly
around the perimeter just prior to finishing (more violinmaking
background - good violin tops always have a thin perimeter 1/4" or so in
from where the top joins the ribs) but very little. Bridge plate is about
0.110 - 0.120. The blackwood is REALLY hard! Should resist the ball ends
of the strings well. The finger braces seem awkwardly high to me - I
peaked them for the hell of it, and I'm considering lowering them a little
to see what effect that has on the tones coming from the ends of the
bridge.

Not that it makes a sizable difference, but the back and sides are
cocobolo - fast becoming one of my favorite instrument woods (I'm even
making a viola right now that has cocobolo ribs and back - very
untraditional, but it's for me, so odd is good )

Pretty much what I thought. The bridge plate did look thick to me but since
your top, for englemann is pretty dang thin that might be a good thing to
provide extra support on the bridge...I'd be cautious at going much thinner
than what you got and don't do a lot of perimeter sanding. I did that on a
really stiff cedar topped parlor one time an dI had to re-top the guitar
because it was building so bad..the top on it was about .110. Of course
cedar and spruce are two totally separate beasts.

All in all it looks like you've done a fine job and I would not do much else to
the top as it looks, aside from the center of the X, pretty lightly done.

_________________
John Mayes
http://www.mayesluthier.com

Its not that there is anything wrong with tap tuning... the reason why many have dismissed it is that it is too subjective. What sounds good on one day may sound different another day.

Yes the masters of the past all used tap tuning, especially in building violin family instruments but even when violins are built to the same shape and size the sound is different, all depending on the ear of the builder.

John's wisdom about spot on... in general with guitars, especially steel strings, if you build to good dimensions for your top and bracing the sound will be very good. There is always room for tweaking but that is the art of it, not the craft.

The school of thought that focuses on glitter pattern tuning is based on the fact that when a tone is generated in close proximity of a top, the top will vibrate at a frequency that is measurable. The purpose of using a lightweight material like glitter is that it is very little and will bounce when the top is vibrated and form a pattern that matches the main resonant frequencies that the top is built to.

Alan Carruth knows more than anyone else here about this. The idea is that the pattern is a better indicator of how focused the sound will be and at what frequencies.

I have always tap tuned but knew it was subjective. When I heard Alan Carruth speak about glitter pattern tuning at the ASIA symposium in 2003? it made sense and I have been doing it ever since. What I really like about glitter pattern tuning is that it gives me a visual presentation that can match up better with what my ear is hearing when I tap tune. When a pattern is too diffused or not focused, I then work on that area to either refine the pattern or to bring down the frequency of the mode I am tryig to tune.

If you search the archives here you will see alot of good references to it.

There is no one method of voicing an instrument, in the end it is all subjective but always based on physical sizes and shapes that are tried and true combined with the experience that is gained over time tapping, flexing, listening and whatever else, all to get to the sound you are going for.

Thanks, everybody. I think I'm close to calling this top ready for assembly.
Now on to side bending! Once I get this one done, I'll post some finished
pics.

My impression from tapping (violins and guitars) is that it takes a lot of
instruments made to correlate what one hears with how the finished
instrument sounds. I just wish I had time to make lots of instruments! I've
got two acoustics, one electric, a viola and a cello in various stages of
progress and it'll be a year or more before they're all done. Oh well. Thanks
again for the advice!!

crazytooguy wrote:
"My impression from tapping (violins and guitars) is that it takes a lot of instruments made to correlate what one hears with how the finished instrument sounds. "

One reason I am so much into the 'glitter pattern' technique is that I just never could get what people were talking about with different systems of tap tuning. This was back in the days before there were videos of it available, but even with those maybe I would not have gotten far with it. But I have no doubt that it works for the people who use it.

To me, there are two advantages to the 'Chladni pattern' technique: one is that it's relatively easy to communicate, amd the other is that it's more objective. When you see a particular pattern at a certain frequency, that's it, and it's not too hard to e-mail somebody a picture of that so that they can check out their own project. Compared to 'a nice clear ring' and 'no dead spots' it's pretty specific.

Sadly, there's no substitute for building a number of guitars to learn any system. I can tell you about the way I work with the patterns, but your builidng stystem might very well give you somewhat different ones. One of my students, for example, seems to normally have two patterns reversed in frequency from what I see on my guitars. He's using my jigs and forms, so it's not the shape, and the bracing paterns are pretty normal, but they just work a little differently. Go figure. His guitars sound good, though, so who's to complain?