tap tone for different body shapes

[labraid]

Hi guys,
My first carved top in the works, an oval hole backpack model, it has a slim body 8.25" wide by 13" long. The mid plate is carved to .236"(6mm) slowly down to .118"(3mm) at the edges. My problem is that without even placing a tone bar in there it taps C5+/-. Does anyone think I should even attempt to carve thinner to get the proper A4#? I do not think it would hurt anything without any tone bar whatsoever, what are your opinions? Am I getting this higher tap tone because the body is narrower than normal, more compact vibrating area, and therefore a higher pitch? Any guesses how this would sound tuned to C5?

Thanks in advance for any help!

-Brian

[sunburst]

It's not easy to tune to specific notes, sometimes it's impossible to tune to specific notes, I don't think it's important that the plates be tuned to specific notes.

6mm is a little thick for me, unless you have a soft flexible top I'd say you can carve your center thinner. How does it feel when you lift, flex, and carve it? Try to make some mental notes for future reference.

No guesses on how it would sound tuned to C. Too many other factors to consider.

[Luthier Vandross]

You need to take a bit more... or your mandolin will lack some punch, and volume.

How are you measuring the tap note?


M

[labraid]

I use the Peterson digital, it has done quite well in the past when I manually set it for the proper note and adjust cents down as the tone lowers, following it.... I carved down a lot more yesterday taking off almost a millimeter in all the places that count and believe it or not the tap didn't change one bit. This mean I still have lots to go? I'm getting sketchy about going too far, ruining it... currently 5mm center, a bit less than 3mm near the rim... C5+10c

-Brian

[sunburst]

That's what I mean about it being hard to tune to specific notes.
I wouldn't worry about what note it is at this point. I wouldn't go any thinner in the recurve unless it's real hard and stiff. The center could be a little thinner, but the note probably wont change if you keep carving.
I'd say you're about done carving this one. You don't want it too thin.

[peter.coombe]

If it is an oval hole - definately do NOT go any thinner.

[labraid]

Thanks for the warning, Pete. http://www.mandolincafe.net/iB_html/non-cgi/emoticons/biggrin.gif Is it because of the lack of support around the oval hole that you say so? The customer says in his 1910-something Gibson oval hole there is one single brace and it is just under the oval hole, horizontally, where one would imagine the most flex could occur. He mentioned dimensions of .5" x .5" x 4". Is this typical as being the only brace in an oval hole? Seems logical I wouldn't need any extra tone bars since the tap tone indicates good stiffness as is, anyone have an idea? Thanks, as I'm new to this carved top business I can use any hints, and they'll be quite appreciated!

Take care,
Brian

[Chris Baird]

The old As have one single transverse brace under the hole. That bracing design has largely been replaced by x-bracing. It would be advisable to x-brace the instrument even though the top is stiff. Bracing certainly changes the way the top vibrates for the better(usually, probably, ...oh I don't know).

[Luthier Vandross]

Agreed on X bracing, as we convert basket case As, with missing single braces.


M