I would begin a journey into the guitar starting with some of the basic physical attributes of sound and psycho-acoustics, explained by everyday example. Then, off on a hike to the frequency mountain tops: First, we wander into the valley of the instrument’s lowest frequency range, below what we can hear: “infra-sound,” the same sound used by blue whales and elephants for long-distance communications, hardly more than the winds, really. Then, wander further down the valley of the low audible frequencies, where we begin to encounter the directionless sounds of the low-end of the guitar’s sound spectrum and the human male’s voice range. Coincidence? This is where the guitar’s body-air mass information is encoded and how the guitar’s “rum-jug” air resonance works—the sounds the guitar makes when you blow or hum across the sound-hole, like whistling over a coke bottle. When you hum the right pitch, the body seems to shake in response. The path begins now to slope up a bit.

About an octave above this body-air resonance note–just about where the typical female voice begins–complexity creeps in: the guitar’s face and back flutter across their entire surfaces, in a phase-relationship which manages to squeeze the enclosed air in each cycle. The wavelength here is still pretty large—roughly five feet. Since there is nothing five feet in size on the guitar that can resonate, it must be created by a point source mechanism: the sound-producing mechanism operating at the sound-hole. The beam resonances haven’t kicked in quite yet. The slope gets a little steeper, and we find ourselves in the foothills of the mid-frequency range.

The third octave of the guitar spectrum starts getting really interesting and complex. Here is where the beam resonances of the guitar appear. The face is seen to rock fore and aft—and from side to side. The asymmetry of X-bracing becomes apparent as the nodal line of the face-rocking rotates from the longitudinal orientation common to symmetric bracing patterns—the rotation putting the sound hole in the anti-node, in the former, to produce the highest point-source sound, while remaining on the nodal line in the latter, and remaining silent.  We have to work now.

The path upward begins to branch into numerous clefts in the frequency mountain-scape. Every guitar follows a different path. As we go up the next two octaves higher, the wavelength halves, then halves again to a fraction of a guitar’s size. We have climbed out of the relative simplicity of the point-source world: no level of human ingenuity can master this landscape.  Its complexity begins to overwhelm our rational senses and a kind of darkness begins to descend upon us. Our analytical mental eye is blinded by the complexity. Now we must develop our other senses and ways of understanding in order to continue the path upward.  Eventually, we will have to let go and simply dream the rest of our way to the summit. But not yet.  

Now we pass into the 6th octave of the guitar’s spectrum. Here’s where a remarkable transformation takes place. Where once we found ourselves in darkness, the world suddenly becomes illuminated with ideas and knowledge. We have reached the range of human voice formants, where we convey meaning and words from one mind to another. To see the voice formants illuminated in their own light, we need only whisper (where the low-frequency information is gone) and where men sound the same as women. Our mind is so finely tuned to extract voice meaning from sounds in this frequency range, that we can not hear the separate frequencies making up the formants, This is where at any given moment during speech, the three resonant chambers of the human voice tract–by changing their size and wall stiffness–form what is essentially a continuously-morphing musical chord. Here is where rational thoughts are conveyed. Here is where ideas, knowledge, and memories are passed around and stored. Stories are told here. To hear the world without voice-formants, simply try humming and try to speak while you are humming. By whispering, you heard the voice formants alone, while by humming you reverse the filter, and find your vocabulary suddenly limited to growls and body language–a very primitive stage in our evolution as humans. We have reached a vast frequency plateau where in fact we spend the bulk of our mental time and effort. Our physical behavior is substantially guided in response to the meaning in the speech we are exposed to: this is the glue of humanity.

The 7th octave leaves voice-formants behind and strangely re-enters the world of subliminal perception. We do not hear voices here, but rather deeper meaning such as pain, fear, anger and joy. This frequency range, with a wavelength of an inch or two, requires a lot of energy to produce. In the human voice it is created by the inner faces of the vocal chords being pressed very tightly together, fluttering along their length in shorter and shorter wavelengths in a manner that can only be created by applying great air pressure from the lungs. Combine a short blast of this with your mouth open like a megaphone, and we call it a shout. Press harder, add yet higher frequencies, and we hear an angry shout. Here we can hear when a crying child is not just whining,–which only uses the voice formant frequencies–but is really sick or in pain. 

At the beginning of the journey, we learned that low sounds travel the furthest. As we approach the highest frequency range, the distance we can hear these frequencies is greatly reduced. At normal levels, they convey intimacy by requiring close proximity to be heard–literally, pillow talk.

When we buy guitar wood, we focus our attention on the soundboard, which is the planar source of all of the higher frequencies. The less internal vibrational damping a piece of wood has, the better it will be able to convey tones of the 7th octave, where love, hate, ecstasy and pain leave their mark on the sounds we make. Such wood, along with fresh, new strings and percussive playing, creates the full suite of low and high frequencies and allows the highest emotional content to be conveyed to the listeners.  

Here is where we finally stand on the tonal summit of our frequency journey. With luck and an open heart, we can imagine shapes in the starscape now visible to our souls. We do not see this, or even hear it. We feel these forms shifting and changing, and we feel the universe expanding away in all directions. Yes, playing guitar is good for you!