Sound - Vibrations transmitted thru the air and received by the ear.
Pure Tone - A single vibration at a specific frequency (Hz).
Fundamental Tone - The initial tone of a musical tone.
Harmonics - Tones that are multiples of the fundamental frequency.
Musical Tone - A tone that is made up of a fundamental tone and a blend of harmonic overtones. Individual harmonic overtones are called partials. The dynamics of this blend affects the quality of the musical tone. Improving the quality of the musical tone is the goal of both the player and the builder.
Dissonance - The combination of tones out of harmonic relation to each other.
Resonance - The natural, sympathetic vibration
of a volume of air or a panel of material at a particular frequency as a result
of excitation by a sound of that particular frequency.
Sympathetic Resonator - A plate that vibrates at the same frequency
as the soundboard thru the transference of sound energy thru the air.
Coupling - Any means of joining separated masses of any media so that sound energy can be mechanically transmitted between them.
Velocity of Sound - The speed at which a material transmits vibration energy.
Lively - High velocity of sound.
Acoustic Damping - Low velocity of sound.
Sustain - The ability of a material to prolong vibration energy over a period of time.
Headroom - The volume level at which sound begins
to break down. The inability of a vibrating plate to control oscillating energy
at a given energy level.
Subjective Descriptions of Sound:
Fat / Round / Full / Lush / Rich - Strong fundamental tone with strong harmonic overtones.
Bright / Brassy / Metallic - Strong upper partials.
Warm / Dark - Strong fundamental tone and overtones at low and midrange.
Mellow - Strong lower partials.
Woody / Dry / Raspy - Strong midrange with a quick attack.
Color - The quality of the harmonic mix.
Thin Tone - Strong fundamental tone with a low harmonic overtone content.
Acoustic Contribution of Guitar Elements:
Strings - The initial source of vibration energy. The musical tone is a function of string tension, string mass, and scale length.
Soundboard - The soundboard affects responsiveness, quickness of attack, sustain, overtone coloration, and the strength and quality of the fundamental tone. It is considered by nearly all luthiers to be the most important acoustic component of a stringed instrument.
Back and Sides - The back is a reflector and sympathetic resonator whose oscillations and sound waves contribute substantially to the harmonic mix.
Bridge - A transducer that converts string vibrations to oscillating motions in the top. Vibrations can be controlled by choosing a damping material such as ebony or a lively material such as rosewood and varying the weight of and configuration of the bridge.
Fingerboard - The fingerboard vibrates in a subtle way and adds mass to the instrument, affecting sustain. Rosewood adds to the harmonic overtones of the instrument, due to it's high velocity of sound. Ebony subdues the overtones and gives a more controlled sound.
Bracing - The bracing pattern on the back of the soundboard and back significantly affects the efficiency at which vibration energy is converted into sound waves. In addition, the acoustic characteristics of the species of wood will couple with the soundboard and color the sound.
Soundhole - The soundhole relieves the sound pressure waves that develop within the soundbox when the top is oscillating. The hole diameter is mathematically linked to the soundbox volume.
Sound box volume - Smaller volumes enhance the
upper end; larger volumes enhance the lower end.
A note about the break in period:
The resins in recently processed wood take time to harden and crystallize. As the wood is vibrated by playing, the resins align in patterns that are unique to the player's technique. For example, an aggressive player may produce a soundboard with stronger fundamentals, and a player with a softer technique may produce a soundboard that develops a slightly richer harmonic content. The guitar literally becomes an extension of the player. The time to set this quality in the soundboard is during the first few years. Red Cedar has a shorter break in period than the spruces. The velocity of sound for all woods increases over time.