A sensitive guitar, by definition, has what engineers call “high average admittance”. Qualitatively, that simply means that the energy from a plucked string is easily admitted to the soundboard in order to produce sound (rather than the energy being reflected back into the string). But at a high average admittance some frequencies have too high an admittance, that is the energy from the string passes too quickly to the soundboard resulting in a clunky sounding note without sustain. The frequencies that these clunky notes occur at are the resonant frequencies of the guitar panels and the enclosed air. So it’s very important, on a sensitive guitar, to place these resonances at the correct frequencies, so that they do not get in the way of the notes you want to play. If a builder has not considered this issue, it means one of two things: the guitar is not a sensitive, responsive guitar (which is mostly the case) or the guitar has a number of very dud notes on it.
It’s unquestionable that at least some of the best Spanish builders of classical guitars knew about this many years ago, but it’s unlikely that they called it “high average admittance” or the term I use (and measure) which is akin to it “monopole mobility”. How do I know? Because the guitars that they built that I have measured show an uncanny predilection for the “right” frequencies of their main resonances. So uncanny that it’s impossible to believe they happened by chance. On the other hand, the steel string builders, being mainly factories, never arrived at the “cusp of disaster” as their manufacturing methods weren’t reliable enough to keep them on the right side of it without expensive and reputation shattering warranty claims.
A further difficulty is that sensitive guitars tend not to play in tune. There is a good (and very) technical reason for this that I won’t go into here, but it can be greatly alleviated by good string intonation techniques, which is why I compensate both the saddles and the nuts of all my guitars.
So tuning a guitar’s resonances to specific frequencies is important (see Modal Tuning), but only if you have a responsive guitar in the first place, otherwise it doesn’t matter, and it’s this path of least resistance that most builders have unwittingly followed by overbuilding their instruments.
The simplest way of describing my design techniques is to liken them to an instrumented version of how the Spanish masters worked. Rather than relying almost entirely on the senses of hearing and feeling, with years of experiential learning, these senses can be augmented (but not replaced) by modern computerised measurement and analysis techniques. This has led me to greater consistency in construction “on the cusp of disaster”, due to better material selection through to performance optimisation of the completed instrument.
My design techniques are very different from those used by others, to the extent that I have written a book (together with my friend Gerard Gilet) describing my design and build techniques. It is the use of these techniques that make my guitars measurably more responsive, louder and more in-tune to the equally tempered scale than most other guitars and they still hold together for the long term. These values I summarise as Sensitivity, Playability, Musicality and Longevity. You can read a brief account of my techniques in the Responsiveness, Playability and Musicality sections by clicking on the relevant buttons below. For the details, you will need to read the book.