Official Luthiers Forum!

I have the book Classic Guitar Construction by Irving Sloan. In the back of the book when the guitar is fully assembled just before finishing he says that he taps the guitar and sands the top until it responds in B, I think it said. How important is this? Is it almost certain that it would sound better?

Let me respond first by posting a disclaimer that this is how *I* build my guitars....

I think it's very important for a number of reasons....

When you brace a top you can do a pretty good job of tap tuning it by shaving braces until you get the sound your looking for. But the minute you glue that top to the rim it all changes, your adding stiffness and mass to the top and it's going to act different, same with the back AND you must keep in mind that the back and top work together. The back may not be as active as the top but it does help in projecting the sound.

In my case when I'm bracing a top I don't want it to have a "high" bonk tone (I love that term) but rather a fairly low one. I don't thin the edges of the top but rather focus on getting the bracing right, and I leave the top a little thick.

Once I have the top attached AND the back on, I pull out my sanding tools and start working down both the top and the back edges, first I smooth and flatten everything down. Then I start tapping and sanding along the edges, what I'm listening for is how 'active' the top is, and I achieve that by thinning the edges to increase top and back movement.

If you think of a guitar like a speaker then you can see why I approach it this way, I also tuck my braces when builing but arch them down pretty thin where they tuck, this helps everything move as well. Another thing that I learned from Ralph Novax was to not let my kerfing be *too* thick, you want the top to vibrate at the juncture where it joins the top. On one guitar I ran side braces and placed the kerfing over those (so I had little feet sticking out into the top), I learned very very quickly what Ralph was trying to tell me, I had a hell of a time getting that top to be active (lesson learned)..

Anyway hope that helps

-Paul-

_________________
-Paul-

Patriot Guitars

Hi Paul!!
This is the best piece of advice I've read on the Forum, about top sound.
It makes a lot of sense!!
Thanks,
WalterK

Colby,

I've only built a couple classicals, but I've played MANY and also talked to many classical builders. I don't have a good method for "tuning" the top, but one thing I can tell you is the best guitars I've ever played all had a top tone between G# and A. I don't know why but all the best guitars I've ever played are in this range. I know this doesn't help much but it's a pretty consistent observation as a player.

Good luck!

John

Thanks for the info guys! It is very helpful and very appreciated. My guitar is responding in G# right now, but I think I am going to play with the voicing some more though. Anymore thoughts are still appreciated.

I should add that I don't tune to a note, I do that because each guitar is different and if I tuned them all to one note I could be missing what that particular guitar really needs. I'm looking more for a proper ring, resonance and tap tone from the top and the back. I don't do Chladni patterns or anything very scientific, IMHO it's too easy to get lost in the science and numbers and miss the tactile feedback that experience brings. And to be honest I build because I like the way guitars sound and feel and if I turned it into all numbers and equations I think it would spoil the fun I have now... I spend enough time at work figuring out data models and architecting enterprise software solutions, I go into the shop to use the other side of my brain

I'm still perfecting my approach and will probably never stop tinkering with it, but so far this has worked very well for what I want to hear from my guitars.

Like I said this is what works for me, I know other builders who do it in a very similar fashion so I known I'm not TOO far out on a limb. I'm glad it makes sense Walter, one other thing to keep in mind is that when you glue on the bridge it changes the equation yet again (you add mass and the tone goes up a bit). So I like a failry deep bonk before I start finishing, in fact I'm beginning to think that I have to re-tune even after I do purfling but I need a couple more on the bench to be sure (and there's more on the way so I'll know soon)..

Cheers

-Paul-

_________________
-Paul-

Patriot Guitars

As is everything in the art of Lutherie, there are many different ways to accomplish similar goals. Daniel Frederich would make his side up to 4mm think whereas others take them as thin as possible. Manual Valasquez would leave his tops thick until it was completely assembled and then by hand sand and thin until it felt right. Others like Al Carruth have done alot of work with Chaldni patterns (which I have adopted and am very happy with).

Pitch is just part of finding the balance needed to get volume, resonance, voicing and other intangible elements all to line up.

As far as kerfing is concerned, even there is there different opinions. Greg Byers uses ash & oak for his linings with a maple main cross brace (!) which at first would seem the opposite of "building light" but it helps him to get the sound he is working towards. You will find as many classical builders that use a stiff rim approach using reverse kerfing and other methods as you find others who insist that a classical guitars top lining should be individual peones (glue blocks) instead of strips.

There is no right or wrong, just the pursuit of the perfect balance of all elements.

A link for those (like me) who are not that au fait with Chaldni patterns on guitar tops. Interestingly from my point of view, the whole planet has chaldni pattern resonations at different frequencies caused by earhquakes.

Colin



Chaldni patterns and guitar acoustics

_________________
I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

Thanks Colin, that is a very interesting site.

I guess from now on it is better for me to forget trying to tune to a certain pitch, and start listening for a certain quality of sound in the tap. Thanks guys!

I'll chime in as somebody who does go the 'techno' route.

First, foremost, and above all: there is no single 'right' way to do this. Nor, indeed, is there a single 'best' tap tone pitch. There are lots of different values that work well for different builders. Just because I get good results with the methods I use doesn't mean that you will.

I picked up on 'free' plate tuning of guitar tops and backs from Fred Dickens back in the 80s. Since then I've been plugging away at it, accumulating data and trying to figure out what (if anything) it all means. I'm getting reasonably consistent and good results with it, and have been able to pass the techniques along to some students who have also gotten good results.

Basically my perspective is that the Chladni stuff tells you three things about the top: the state of 'balance' between the braces and the top, the distribution of mass and stiffness, and the overall ratio of stiffness to mass. I think the first two tell you something about how the guitar will sound, and the third is a structural indicator.

Similar shapes tend to have a similar sequence of resonance modes. All strings, for example, produce harmonics if you touch them at the 1/2, 1/3, or 1/4 points and pluck near the bridge. Strings are simple and guitar tops are more complicated, but the principle is the same. A really tight string will have it's lowest frequency pretty high up, and the harmonics are multiples of that. Same with a stiff top: high frequencies for everything. Some of the 'signature' modes of the 'free' top are good indicators of whether it's stiff enough to hold up under string tension. Of course, you have to take the weight into account as well: a top made of dense wood like fir will tend to have lower modes at a given stiffness than one made of, say, Englemann.

If you get the brace angles 'right' you are likely to see a particularly 'well formed' set of resonance mode patterns. You can feel this, too, when you flex the top; the stiffness tends to be much the same along the lower bout as across it. The patterns give you a bit more information, though.

In particular, if the top is 'lumpy' the patterns will be too. Looking at the paterns can help you figure out just where to remove wood to get the smoothest patterns. When you get them right it seems to me that you've set up a condition where neither the top nor the bracing is taking too much of the load: there are no concentrations of stress. You can learn to feel those lumps, too.

David Hurd has been using static deflection measurements to get a lot of the same information, I think, as he detailed in his book 'Left Brain Lutherie'. He's more into math than I am, but don't let that throw you.

Finally, just FYI: I've seen good guitars with the completed 'main top' resonance mode (the pitch you hear if you block the soundhole and tap on the bridge) between about F and A#, iirc. Generally as that goes higher you get a more 'treble balanced' sound, but that's about it as far as I can see. I think the exact balance between the bracing and the top is far more important than the pitch of the tap tone, in terms of things like clarity, color and balance. I've seen a couple of instruments that had tops that felt like marshmallows that still had nice clean trebles, and ones that were stiff as all get with good bass. It's in the details, and however you can get those right, that's great.