Fine tuning archtop guitar plates

[Jean-Pierre Laplante]

In his classic book, Bob Benedetto describes in detail how he "tap tunes" the top and back plates. On page 77 of his book, he ends his description of the overall process with the following comment: "...Tap tuning is an intuitive skill which takes many years of experience to develop and perfect. We learn by doing...". If one intends to focus his career on building exclusively acoustic archtop guitars, then it's certainly worth building a few dozens to get the feel for the "right way" to do it. For the rest of us, mere mortals building only a few a year, the whole process often ends up as a hit or miss: some guitars turn up really nice while others are, let's say, average...

2-3 years ago, I had the idea of using the Tonerite frequency generator to help me in the final critical step of fine-tuning the top and back plates once they are glued to the sides. I must admit that I'm really happy with the results and using the generator has allowed me to get, tone wise, more consistent instruments. So here's a link to a video that I made showing how I do it.

https://www.youtube.com/watch?v=suNA0I7ocsQ

It's very likely that somebody else has done that before me and I would appreciate if you'd let me know if you're aware of someone so that I can give him/her proper credit.

So let me know what you think!

[Eric Knapp]

That's fascinating to this rookie builder. I'm going to check out that generator when I eventually start my first archtop. Thanks for posting.

-Eric

[Randolph Rhett]

It reminds me some of Alan Carruth's plate tuning DVD. His is a more involved technique, but also relies on external signal generator exciting the top. I bought his DVD almost 10 years ago, watched it once and lent it to another student luthier. Unfortunately, he returned to Germany having never returned the DVD to me. I am a little vague now on exactly what Alan did, but I do remember that the technique was applied to a flat top and arch top guitars.

[Brian Evans]

I liked that video, as much for the idea of the tone-right as to confirm that what I am doing when I tap tune is about the same process. I listen for the tone - the pitch - of the plate, but far more than that I am feeling all over for the uniformity of the vibration. Particularly when I tap the top and feel the back. that's how I tuned the back recurve. Very cool.

Brian

[Jean-Pierre Laplante]

Wrt Randolph comment. Alan was then using Chaldni patterns. He seemed to get good results with his flattop when he could get a specific pattern for the top. I played with that too but wasn't patient enough maybe to pursue that avenue! Moreover, t that time I had already made the shift to archtops and that technique can't be used for 3D top and backs like in archtop.

This being said, I still tap tone my top and back but once they're glued to the sides, I rely mostly on what the Tonerite generator tells me. So I consider that technique more as a means of finetuning the plates than a way of bypassing the initial tap tuning process. Still, it helped me tremendously over the last few years.

[Alan Carruth]

I first learned 'free' plate tuning from Carleen Hutchins, who did a lot of the work developing it as a technique to use on violin family instruments. From there Fred Dickens started to apply it on Classical guitars, and I tried it on steel strings. It certainly does work on archtop guitars: I've used it on all the ones I've made.

I wrote a series of articles in 'American Lutherie' back in '91 and '92 where I went into some of the theory behind plate vibrations, and how I applied the technique to violin family instruments, and arch top and flat top guitars. We've all learned some things since then, I hope, but it's still useful information. Basically, on flat tops you work mostly by adjusting the stiffness of the bracing to get it to work well with the top (or back), and also to end up with the two plates adjusted to work well together once they're glued to the rim. On arched plates it's a little more complicated. There's less bracing (and none on the back), so you have to work with the stiffness and mass distribution of the plates themselves in large part. Since the stiffness is a function of arch height and shape, as well as the thickness distribution, there are several things that you have to get right at the same time. It's not impossible, and, in fact, is much more straightforward on arch top guitars than it is on violins, where the sound post really complicates things.

That said, there's a lot more to making a good instrument than just getting the 'free' plate modes right. For example, arch top instruments respond strongly to thinning around the edges, which doesn't make a lot of difference in the 'free' plate modes. Setup matters too: too much down bearing on the bridge, or the 'wrong' tail piece setup, can kill the sound of an otherwise 'well tuned' instrument. You obviously need to use your wood right, matching the arch height and shape to the characteristics of the wood, and the desired sound. It's a system, after all, and can't always be redeemed by getting one part right. As the saying goes; it's not much use putting lipstick on a pig.

[Jean-Pierre Laplante]

Hi Allen, I must admit that I missed your input wrt your technique as applied to archtops. I was away from the forum for quite some time so I'm trying to catch up! Still not old enough to stop learning...

P.S. I still have and use the scaper you gave me at the last Montreal Guitar Show. Thanks again for that great "one of a kind tool".