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My comment was meant to be a joke, but I guess it could be taken seriously.
I have innovated exactly zero point zero things with my guitars. Everything I do has been done before. Including my mistakes.


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http://www.CostaGuitars.com
PMoMC

Well, as ever, it's not a case of just one type or the other. Both live and non-live backs have their very valid places. As I've said before, (and very simplistically) stiff backs give "volume" and live backs give "tone". Floppy backs (as Mike has suggested) kill both. It's a case of knowing what the alternatives offer and when to use them.

For guitars played acoustically I generally use a live back with a 3m radius dome (that's about 10 feet). Not seven, but I wouldn't want to bind a back with a Venetian cutaway with a seven foot radius. 3m radius makes it difficult enough. The majority of my SS guitars have Venetian cuts.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

I'm not sure I said "loose floppy back".

I just said the back's influence makes the tone more complex, and lessening it's influence makes the top's influence dominant.

The back doesn't have to be loose and floppy to contribute.

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Old growth, shmold growth!

Having checked back, I'm sure you didn't!

I was just making the point. Both live and non-live backs work fine, which means giving them the right degree of stiffness for the job. I've seen/heard a few floppy backed guitars and acoustically they don't seem to do anything well.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

OK, here's some more technical terminology:

Live backs produce a T(1,1)3 resonance.

Non-live backs don't produce a T(1,1)3 resonance.

Floppy/loose backs have a T(1,1)3 < T(1,1)2 (which is not strictly correct use of the nomenclature, but those who know will understand )

Is that better?

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

" D T's" - delirium tremens - a.k.a. "shaking frenzy" ?

Not really. Filippo

I'll say!!

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jw ( o)===:::

What he's saying is that a live (not floppy) back contributes frequencies making the tone character more complex. A floppy back will contribute wolf tones and tuning dissonances.

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Old growth, shmold growth!

Not to mention what her and her cast of characters did for Canadian luthierie

OK, here's a longer version.

Typically, if you do Chladni patterns on a guitar top you'll see either two or three occurrences of a main monopole resonance. A non-live back guitar will show just two, the two parts of the air/top couple. A live back guitar will show three, the three parts of the air/top/back couple. Typically the frequencies of these resonances are ~100Hz, ~200Hz and ~250Hz if you have those resonances placed according to my processes. These resonances, if present, will also appear as peaks in the guitar's frequency response curve (elicited, for example, by recording taps into a spectrum analyser). Whilst there are other naming conventions, the one I use names these resonances the T(1,1)1, T(1,1)2 and T(1,1)3; T stands for Top, the first two digits count antinodes across then down the vibrating surface and the third digit denotes the frequency order in which they occur (lowest first). So a T(1,1)1 resonance is the first (in frequency order) occurrence of a top monopole resonance, sometimes called the fully coupled main air resonance or (incorrectly) called the Helmholtz resonance. A T(2,1) resonance is a cross dipole.

So, if you can find an active T(1,1)3 resonance you have a live back guitar. If you can't, you have a non-live back guitar. Normally the T(1,1)3 peak, which shows the back coupling into the system, has a frequency greater than the T(1,1)2, as the nomenclature would suggest. If it is lower, the nomenclature falls apart a bit as the T(1,1)3 normally refers to the back's contribution. However, if it is lower, all sorts of things happen which I don't like the sound of (hence "kills volume and tone").

The T(1,1)3 in its "normal" region can have a bunch of beneficial effects which I won't go into in detail, but can add to the complexity of the sound (tone) at the expense of a bit of volume. Not having a T(1,1)3 saves you that volume loss, so, simplistically gives you "volume". However, if you make a very sensitive, loud, guitar, using a live back can stop it from becoming too raucous, with associated wolf tones, so you get a nicer sounding guitar if you give it a "proper" live back in those circumstances.

There are certain mobility criteria that have to be observed to ensure a live back, and a bunch of frequency relationships to take care of between the main T(1,1)x resonances so that things work as intended. It's easier to make a non-live back guitar, because you just make the back stiff/heavy and don't have to think about it any more. Getting a live back guitar right is more difficult and harder on classical guitars. Getting it wrong can give you the floppy back scenario, which in my experience is never good.

More, as ever, in the usual place.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

"Floppy" to me just means a T(1,1)3 that is too low, typically below the T(1,1)2. You can get that by going with a back that is too thin, too dense, not enough bracing, etc. etc. all the normal things that reduce resonant frequencies. What it does is absorb too much energy as it vibrates, so killing volume, and can produce a "phasing" muddy sort of sound if the T(1,1)2 and T(1,1)3 are too close together, irrespective of which has the higher frequency.

I don't know that I'd be so "black and white" about it. However, it reminds me of this quote (Domingo Prat) about Torres' "cardboard" guitar:

"...this guitar has an extraordinary sound, if perhaps a little muted, bland and low, as the author of this dictionary was able to confirm when he played it in the house of Tarrega."



If I was going for a live back I'd be avoiding heavily damped timbers just because they're harder to get them moving and keep them moving, so stealing more energy from the top to get them to work.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au