Why the traditional sound hole?

[luecack]

I was gonna say tradition and aesthetics, but I am quite partial to this.

[Gordon Currie]

OP: I've played a Skytop guitar at La Conner in 2018. Eric knows what he is doing and why. The tone is somewhat different from the traditional sound - in a good and usable way.

To me, the most interesting aspect of a top without sound hole is that it frees one up from many traditional bracing patterns. Since the bracing pattern can intimately affect the tone AND response, that is an area I hope gets more experimentation and innovation.

[Sadie-f]

Originally Posted by Alan Carruth

koolimy asked:
"...does this coupling effect happen with both steel string guitars and classical guitars? Or are the differences in construction and bracing too drastic so that one loses this effect?"

It can. What matters most, aside from the outline and hole location, is the pitch of the 'long dipole' resonant mode of the top. The couple that produces the 'extra' output peak is between a resonance where the air 'sloshes' the length of the box, and that top mode, where the bridge is rocking forward and back, and the lower part of the top moves a lot. That top movement can 'pump' the air sloshing, and the air pushes on the top, so they work together. Normally that air resonance doesn't produce much sound at the hole, but with the influence of the top the configuration of the 'air' mode can change, and it can make a lot of sound at the hole.

What's interesting is that the popular 'standard' bracing schemes for both classical and flat top steel string guitars tend to put that top resonant mode in about the right pitch range to couple well. Other resonances, and particularly the 'cross dipole', will be different in the two brace schemes, but the 'main top' and 'long dipole' pitches tend to be conserved. I suspect that's not accidental.

"Also, what does this extra resonance "mean" to a layperson?"

Without this couple there tends to be a gap between resonances around 440 Hz, the fundamental of A at the 5th fret on the high E string. The couple tends to fill that range in a bit. But there's probably more to it than that.

In many respects the acoustic guitar is 'about' complexity. A plucked string produces a signal that is predictable, and somewhat boring by itself. The guitar body is an 'impedance matching transducer' that takes that string energy and converts it to sound in the air. In the process it 'shapes' the sound, emphasizing some pitches and limiting others. This gives different timbres to the string sound depending on the fretted pitch and how and where on the string you pluck it. Since your senses are generally set up to detect changes this makes the sound more interesting. A good guitar will allow the player to vary the timbre through a fairly wide range by the way they play, and much of that variation depends on having a complex resonant structure. The design of the guitar has evolved to facilitate this in particular ways. The result is a 'guitar like' sound. A player or listener may not home in on any particular aspect of the tone; the whole is greater than the parts.

Well said Alan!

And also this:

That little round hole and that bit of wood, that’s the truth.

— KEITH RICHARDS

Russel, on a more serious note, one of your points is about sound ports. I'm not against sound ports, however adding one is a concession to the guitarists who want optimal sound projecting to their playing position. Makes perfect sense, a while back on a whim, I tried shifting my OM to classical position, and was quite surprised at how the guitar's tonality shifted as the sound board / hole came out of the shadow and I could hear the guitar more directly with my left ear.

This doesn't mean I'm running out for a sound ported guitar, or playing in classical position. Afaik, Santa Cruz and probably lots of other shops decline to build sound ports. I support that, while I don't perform professionally, ultimately I want my axe to sound best to listeners.

[Alan Carruth]

I'm never going to argue that we should reject better ways to do things. As with most luthiers, I'm always on the lookout for a better way. Define 'better'.

Technological evolution is cultural: we're always trying to come up with something that works better in the current context, whatever that is. For those of us making guitars the context is the music people play on the, and the venues they preform in. What ever we make has to be useful for existing music, facilitate the evolution of new music, and be usable and audible in the settings where people play it.

One of the problems with innovations is that they can produce an instrument that is, in some way, unsuitable for the existing repertoire, even when it solves some other problem. 'Lattice' top classical guitars are a good case in point. The top design has been pushed in the direction of minimal weight within the more or less 'standard' size and shape, and with sufficient stiffness to hold up well. This enables the guitar to produce more sound with the limited power of plucked strings. The problem is that keeping the stiffness up while reducing the mass shifts the normal resonances upward in pitch, changing the fundamental timbre of the instrument. This leaves it less useful for works that were written on guitars that had more 'normal' resonant pitches: they just don't sound right. One solution for this would be the simply develop a whole new repertoire that exploits the new timbre, and over time that may well happen. But it won't be Sor and Albeniz, or even Brouwer or Domeniconi. This sort of thing has happened any number of times in the history of music. One time was when the guitar replaced the lute, and more recently we saw the revolution wrought by the solid body electric guitar. Lutes are still played, of course, and there is even new music written for them. Rock and Roll didn't replace acoustic country music.

In some respects the success of the standard designs has worked against them. Given the limited power of a plucked string there has been strong pressure to improve the efficiency of the instrument. The result is that at some pitches a good standard guitar is very close to 100% efficient (with the limited power it's hard to measure). The most notable of these pitches is the infamous 'thuddy G'; the so-called 'main air' resonance that causes problems when it matches the fundamental of a played note too closely. The guitar is so effective at changing string energy into sound at that pitch that you end up with a note that's twice as loud as the ones on either side, but for only half as long. We don't notice the extra power so much as the lack of sustain. Extending that performance; making the guitar similarly efficient over a wider pitch range or at other frequencies, tends to produce other problematic 'wolf' notes. In general, the better the guitar is the more likely it is to have these problems. With care that can be kept under control, but that requires a
lot more individual attention than can be mustered on a production line.

I'm being called away, but will try to get back to this when possible.

[Mayfair]

Originally Posted by brencat

Don't care for the look of offset soundholes or anything avant garde for that matter. Put that stuff in a museum please, and not in my lap

I'm late to the party, but my first thought was "symmetry."

[Alan Carruth]

As Pye said: "...when the need is old, the old ways will probably be the best, unless some new technique has been introduced..."

So long as what you're looking for is a 'traditional' sound, and you're using wood to make it, you're going to find it hard to improve on the standard designs by enough to make it worthwhile. Guitar players will move to something new very quickly if it's actually an improvement: Torres' designs pretty well replaced the older ones in Spain within about fifteen years of being introduced, despite the fact that Torres himself couldn't make a living building them. Most of the 'innovations' that are being talked up here go back decades, if not centuries, and they have yet to replace the standard designs.

If the need is not old; if you're trying to play in much larger halls than the standard designs can handle, then some new technology is probably in order. The 'lattice' top classical guitars have caught on with concert players who try to eschew amplification, and still feel the need to play in large halls to make an adequate living. The harsh timbre smooths out a lot in the bigger venue, especially with a big audience to soak up some of the highs. It also helps to have world-class chops.