Mandolin Tap Tone - Questions

sebastiaan56 · Post by **sebastiaan56** » Wed Dec 05, 2007 1:37 pm

Hi Everyone,

Im in the middle of carving the top and back of an archtop Mandolin. Basically a diminutive L5. Ive rough carved the plates and am sanding tapping as I go. With the top Im currently hearing is the tonic and an octave and an octave three above the tonic. No discernable fourths or fifths or second octave. The first octave is by far the strongest.

Where do I stop? Im really tempted to bail out now and start cutting f holes and adding tone bars. What happens when you go too far? I dont have the cash for more tops right now.

BTW the timber is a piece of KBP from Tim. Very nice!

Sebastiaan

graham mcdonald · Post by **graham mcdonald** » Wed Dec 05, 2007 4:26 pm

Hello Sebastiaan

How thick are you carving the Kig Billy and high high is the arching, and what note/octave is the fundamental pitch at the moment?

graham

sebastiaan56 · Post by **sebastiaan56** » Wed Dec 05, 2007 4:48 pm

Hi Graham,

Arch is 15mm, its 6.5mm in the centre and 4.5 at the edges. Its currently playing about 10c flat of an E flat.

Sebastiaan

graham mcdonald · Post by **graham mcdonald** » Thu Dec 06, 2007 6:12 pm

Eb is not where I would want a mandolin soundboard to be at this stage, but a bit hard to tell without knowing what octave. 6.5 in the centre is pretty thick, but King Billy usually wants to be a bit thicker than spruce. One critical factor is the thickness of the recurve, and a good rule of thumb there is 40% thinner that the centre, so a 5mm thick centre should be 3mm at the thinnest part of the recurve. I usually aim for a a mandolin soundboard to ring at somewhere between F and A before cutting soundholes and gluing braces, but that is a for a teardrop body out of spruce and a small guitar shape out of King Billy might be a little different and an oval hole instrument will be different from an f hole top.

An spruce f hole mando top can be down in the 4.5mm range in the middle, while an oval hole instrument needs to be up in the 5-6mm range. I would add 20% to that for King Billy and see how it goes.

Good luck with it

cheers

graham

sebastiaan56 · Post by **sebastiaan56** » Thu Dec 06, 2007 6:58 pm

Thanks Graham,

What is most encouraging is the length of the boooing. It gets longer as I remove more but your comments on thickness of KBP have stopped me. Im going to leave it at what it is and cut the holes, add the tonebars etc. I guess it can always be further sanded before final finishing.

Sebastiaan

Hesh1956 · Post by **Hesh1956** » Fri Dec 07, 2007 12:03 am

Sebastiaan my friend I have nothing to add but that never stops me.....

I bought the book below thinking that it would have something useful and interesting regarding tap tuning a guitar. Unfortunately it is really all about the mandolin - you might find it interesting.

sebastiaan56 · Post by **sebastiaan56** » Fri Dec 07, 2007 5:39 am

Hesh,

I'll PM you mate, what can I say, you're a bluddy gem! I wont be travelling for a while but one day you've got to get yourself and a couple of those loverly Heshtones to Aus so I can buy you a drink, and make some noise together. I reckon we could set up a billet trail around the country for you!

Graham,

Ive cut the f holes and added the tone bars and now there is a dead spot in the middle of the plate where the bridge will be. I expected this but should I keep on thinning the plate to get more a more vibrant response from this area? I used the two tone bars rather than a cross.

Do you profile your tonebars like in a guitar or keep them flat?

Sebastiaan

graham mcdonald · Post by **graham mcdonald** » Fri Dec 07, 2007 8:55 am

Don't worry about a dead spot in the middle. I suspect it isn't, just an area that is not being activated by whatever vibrational mode you are exciting. The whole field of freeplate tuning is one that is still open to lots of debate. However it is done all any of us are trying to do is make a soundboard of a stiffness that is strong enough to withstand the tension of the strings while keeping the mass of the soundboard to a minimum. Experimentation has shown that soundboards which have their vibrational modes around specific frequencies work better than when those frequencies are out of that range. It all gets complicated by the fact that when the soundboard is glued to the ribs, all those vibrational patterns change and I don't think anyone has worked out the relationship.

All that notwithstanding, knowing what the free plate modes are is a useful bit of information. If the plate goes bong at note X and the finished instrument works, you have done something right. If it bongs at note Y and the instrument sounds like a chunk of 2x4 fence post, you make a note of it and start another one. What is frustrating is when a soundboard that shouldn't work because the tap tone is wrong makes a cracker of an instrument. As I said, a useful tool, but not the final word.

It also depends of which mode you are listening to. I hold the soundboard about the 10 o'clock position and tap at around 4 o'clock, which I think excites mode 4 (but I might be entirely wrong). Holding it around the tailblock and tapping it in the middle excites a different mode. , but the 10o'clock/4o'clock mode is the one that changes as thickness.braces/soundholes are added or removed.

A lot of it is just practice, listening to a lot of soundboard being tapped and trying to drill that into the memory. It would obviously be better when you are doing it all the time, rather then on weekends and the ocassional evening.

If you have used tone bars and f holes I would be inclined to thin the top down to around 5mm in the centre (Most Loar F5s are around 4mm) and 3mm in the recurve 15-20mm in from the edge. Ignore Siminoff's rave about tuning the tone bars to separate notes. It is, as a colleague puts it, 'star trek physics'

cheers

graham

sebastiaan56 · Post by **sebastiaan56** » Fri Dec 07, 2007 9:51 am

Thanks Graham,

I was wondering about what happens to the tone when the back and sides are on. It doesnt function as a Helmholz resonator so there is no mathematical way that I could see to work it out. I guess the specifics of each piece of timber would affect the whole equation as well.

Again many thanks,

Sebastiaan

graham mcdonald · Post by **graham mcdonald** » Fri Dec 07, 2007 10:46 am

The vibrational modes of a free plate are quite different to one where the edges are fixed. UNSW has a very useful web page which has lots of info at http://www.phys.unsw.edu.au/music/

cheers

graham

sebastiaan56 · Post by **sebastiaan56** » Tue Dec 18, 2007 12:14 pm

A public thanks to Hesh for his generosity. Yes, the book and DVD arrived yesterday, only 7 days from chilly Michigan which must be a record from US Post,

Thanks Matey!

Hesh1956 · Post by **Hesh1956** » Tue Dec 18, 2007 2:04 pm

Wow that WAS fast!!!! Amazing.

Hope that it serves you well my friend.

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Mandolin Tap Tone - Questions

Mandolin Tap Tone - Questions

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