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Top-tap
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=30147		 Page 1 of 1
Author:  alan stassforth [ Mon Nov 29, 2010 11:45 pm ]
Post subject:  Top-tap
So, I started comparing thumping the top at various stages of building 2 gits,
and this is what I'm getting.
Koa back, not installed, a nice bong sound, the note D.
Glued on to git, still the note D
Top is really good sitka, instrument grade, top and back thump, D.
Other build is top installed to the sides only.
Nice bong sound, note= A.
So, does the note that rings out matter?
Would the one that sounds in D work better for a D tuning?
Guess I'll find out.
Any input?
Author:  bluescreek [ Tue Nov 30, 2010 6:57 am ]
Post subject:  Re: Top-tap
to a degree , you would like to have the top and back at least a semitone apart.
Author:  alan stassforth [ Tue Nov 30, 2010 10:23 am ]
Post subject:  Re: Top-tap
Thanks John.
So I'm guessing if I wanted to lower the note,
I would lighten the bracing up?
This is getting fun!
Author:  arie [ Tue Nov 30, 2010 11:13 am ]
Post subject:  Re: Top-tap
for me I don't think I'd want any part of the guitar to resonate in a "standard" note or a tuning such as open D. I'd try to go at least sharp or flat in any direction as john suggests. the possible wolf notes could be a disaster if otherwise.

to lower pitch, you could shave some bracing or thin the coupling areas of the bracing junctions. or you could thin the plates at the kerfing.

to increase pitch you need to add mass ie: wood, or increase plate stiffness through various means -harder and/or thicker finish (to a point) or if it's really bad, add mass via small wood patches in select areas etc...
Author:  ChuckG [ Tue Nov 30, 2010 11:17 am ]
Post subject:  Re: Top-tap
You might be interested in Roger Siminoff's works on tap tuning. He uses a strobe tuner (you can get software for your PC) to set the different parts to specific notes. http://www.siminoff.net/ Give him a call - he's a great guy and has been very helpful to me.

Good luck!
Chuck
Author:  alan stassforth [ Tue Nov 30, 2010 10:09 pm ]
Post subject:  Re: Top-tap
Interesting, thanks!
At least I'm on some kind of track.
I should do some research on da subject.
Wolf tones, yikes!
I might actually like that!
Oooowwww!
Author:  John Arnold [ Wed Dec 01, 2010 12:20 am ]
Post subject:  Re: Top-tap
Quote:
to increase pitch you need to add mass ie: wood, or increase plate stiffness through various means

Mass and stiffness are opposites. Increasing mass will lower the pitch. The reason reducing the height of the bracing lowers the pitch is because it reduces stiffness more than mass.
Author:  alan stassforth [ Wed Dec 01, 2010 1:34 am ]
Post subject:  Re: Top-tap
So, there be a few things going on here, ha!
My simplistic thinking is a git-top is like a drum skin.
Loosen it it, lower note.
Git top, make it flimzier, more lower note.
I be taking more notes as I build.
Dat good right?
So, John, thicker top, more bass?
Might lead to some thick top voicing at the edges,hmmm.
Author:  arie [ Wed Dec 01, 2010 11:38 am ]
Post subject:  Re: Top-tap
John Arnold wrote:
Quote:
to increase pitch you need to add mass ie: wood, or increase plate stiffness through various means

Mass and stiffness are opposites. Increasing mass will lower the pitch. The reason reducing the height of the bracing lowers the pitch is because it reduces stiffness more than mass.


yeah, you're right. i got it mixed up again. sorry.
Author:  Alan Carruth [ Wed Dec 01, 2010 2:36 pm ]
Post subject:  Re: Top-tap
alan stassforth asked:
"So, John, thicker top, more bass?"

I'm not John, but I'll venture an answer anyway.

For a given piece of wood, as you make it deeper/thicker, the stiffness goes up much faster than the mass, and the resonant pitches tend to rise. This would lead you to expect a guitar with a thicker top to be 'less bassy', but it's not that simple; much of the bass response, for example, comes from the air in the box and the soundhole size and location, not the top itself.
Author:  alan stassforth [ Wed Dec 01, 2010 10:43 pm ]
Post subject:  Re: Top-tap
Thanks for the replies.
What I'm going to do is keep it similar to sizing braces and tops that I am doing now,
try getting it amplified with a microphone, and use my ear and a tuner,
tune the top and back a semitone different,
take notes,
and build a whole bunch of guitars to figure it out.
I ain't shelling out the bread for a strobe tuner though. duh
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