There are a few basic techniques the right hand can apply in order to accomplish more sound. First, velocity equals volume. Moving a finger very slowly across a string will produce a soft sound, while moving across a string quickly will result in a louder sound. Another musical example of this phenomenon happens on the violin. The faster the bow stroke across the string, the more volume one hears. Accordingly, flexing the fingers at a fast pace across the strings will ultimately create more sound. Another way to increase the volume of a string is a bigger follow-through post-stroke. More follow-through equals more volume due to the energy applied at the beginning of the stroke. An analogy is the automatic follow-through that happens to a baseball pitcher’s arm after he throws the ball. Moving across the string quickly causes more follow-through automatically.
Depressing a string inward toward the sound hole, or “digging in” is another way to increase volume on the classical guitar. When a string is plucked with more force greater amplitude is created, which equals more loudness. Classical guitarists understand this method best when applied to rest stroke. While we all strive to match our free stroke and rest stroke sounds, rest stroke is ultimately louder because the string moves more. But this same effect can occur with free stroke if the player pushes the string inward while flexing the finger during the stroke. For example, when the top note of a three-note chord functions as a melody and needs to be louder than the other notes in the chord.
Fingers have three joints—tip, middle and basal. The tip joint can be used to effect tone and volume on the guitar. By slightly firming the tip joint the finger becomes more rigid against the string. This creates more tension between the string and finger, thus causing a quicker and harder release. Consequently, a softened tip joint can produce a quiet, less focused sound. This can be used to make a special or unique tone like a whisper.
While guitarists are well aware of the tone color differences according to placement of the finger on a string, placement of stroke can also effect volume. In general, if a player’s right hand is over the fingerboard, or playing tasto, the sound may be darker and softer. Strings are tighter near the bridge, so striking closer to the bridge (ponticello) may allow for a brighter louder sound.
The right hand is the voice of the guitar. In addition to color and tone quality, the right-hand fingers can greatly vary dynamics on the guitar. The more access a player has to volume, the more dynamically effective they can be. Playing loudly requires more effort, so practicing these techniques are key. Which technique to apply depends on tempo and what other simultaneous techniques are being employed. For example, if you are playing very quickly, it might be impossible to follow-through more. Choosing which specific technique to use in order to increase volume will take some time, but the pay-off will be worth it.