The Mystery of Doubleback Guitars

Construction and repair of Classical Guitar and related instruments
Alan Carruth
Posts: 3251
Joined: Mon Dec 24, 2007 6:56 pm

Re: The Mystery of Doubleback Guitars

Post by Alan Carruth » Sun Apr 19, 2009 2:19 am


One of the students in a shop where I worked made a very simple device to hold the guitar away from his body when he played it standing. It was a stick with spacers and a couple of clamps on the ends. You clamped it onto the sides across the back, the spacers held the stick away from the back, and the stick held the guitar away from your body. Worked great.

It is possible to make all sorts of sound measurements these days that were quite difficult to get even twenty years ago. A computer with a decent sound card, some free or cheap software, a microphone, and a few other odds and ends are all you need. You can very simply apply a standard 'pluck' to a guitar with the 'wire break' method. Get some fine magnet wire; dead electric guitar pickups are good sources. Loop a short length of this wire behind a string, and pull on it until it breaks. The quality control on copper wire is so good it will always break at the same force, within about 10%, and you can control the exact plucking point and direction easly to boot.

I've got file folders full of charts of all sorts of interesting measurements of guitars that I've made, and other guitars of all kinds that have come through the shop. The problem is not making measurements, it's figuring out what the measurements mean! For example, people talk about 'loudness' as if it were a simple thing to measure, and it's not. 'Loudness' is a perception, and there is no simple way to correlate that perception with the things, like dB levels at particular frequencies, that you can measure. We're making slow progress at finding useful correlations, but it takes time. If better guitars would defeat global terrorism, we'd get a lot more funding! Ah well.

It's interesting that the guitar seems to be one of the more efficient instruments, in terms of turning input energy into sound. The violin, for example, seems to be about 2% efficient, while the guitar is more like 5%, or maybe a bit better. The thing is that most of the 'big' instruments have ways of getting a lot more power in. The bow essentially plucks the high E string on a violin 660 times per second, at exactly the right time to replenish the energy it lost to sound and heat. No guitarist has a tremolo that fast! The piano and harp use 'way more string tension, and much more force to activate them. Wind and brass instruments are abysmally inefficient, but they can put in many times the power we can. We can't take the easy way out, of putting in more power. The ways to do that are to use higher action, heavier strings, or longer strings. Most players resist all of those options: they're already working as hard as they can.

The very efficiency of the guitar makes it hard to see how we could make large gains. It's not too hard to make a louder guitar, but making a louder one that a majority of players and listeners like is another matter. We are constrained by tradition, after all, in the sense that the existing repertoire was written for the sound of the 'traditional' guitar. You can't depart too far from that sound without running into resistance, and you can't easily make big changes in the structure without departing from that sound.

I'm not saying we can't make better guitars. I am saying it's not going to be easy. Right now I'm trying to figure out how to make instruments that consistantly as good as the best that have been made in the past, and, more importantly, to understand why the good ones are so good, and to do so in a way that can be communicated and understood by other makers. It's all well and good to have the 'magic touch', and that sort of thing can make one very successful. It doesn't do a lot to advance the wider world of the guitar in some ways, though.

Finally, I'll note that 'double backs' have been made for a long time; it's an idea that comes and goes. IMO, if it were all that good it would be standard practice by now. It's not as if the idea was not something that any guitar maker couldn't think up, or work out the technology for. This suggests that either it's very hard to get right with traditional technology, or it doesn't work all that well. I suspect it's the latter, since putting in another large vibrating surface adds all sorts of complications that can easily cancel out any gains. It's possible that with the technology we've got now, such as better glues or different materials, it can be made to work when it could not in the past. It's also possible that the modern ear will like something that was not heard as desireable in the past.

In the end a 'hundred flowers will bloom': there's no way to stop them! Over time the market will figure out what's good and what's not. Maybe in a hundred years everybody will be playing sandwich topped and double backed wedge bodies guitars made of carbon fiber, with side ports, and they'll all see the Fletas and Hausers as quaint. Then again, maybe they'll have forgotten the guitar entirely. The lute fell, and the harpsichord, the guitar's turn will come.

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Arash Ahmadi
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Joined: Thu Oct 05, 2017 7:38 pm

Re: The Mystery of Doubleback Guitars

Post by Arash Ahmadi » Mon Apr 15, 2019 9:15 pm

I feel like it does make the sound warmer... But a luthier once explained to me that unlike single back guitars that after you pluck them you'll hear a clean run until the sound dies away, double backs tend to somehow echo the sound in a way so the volume doesn't die away normally like a decrescendo but the volume somehow shifts up and down until it dies away. How do you feel about that? Do you find that to be true?
Becoming a great musician is about becoming a great human being.

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