On a harpsichord, dynamics are controlled primarily by the player's touch. The louder the player presses on the keys, the louder the sound will be. This is because the harpsichord's action is a direct one, meaning that the force applied to the key is directly transmitted to the jacks (levers that pluck the strings).
Additionally, some harpsichords have a soft pedal that can be used to reduce the volume. This pedal works by shifting the keyboard sideways so that the jacks pluck the strings at a less advantageous point, resulting in a softer sound.
Timbre
The timbre of a harpsichord is primarily determined by the materials used to make the strings and the soundboard. Different materials produce different timbres, with harder materials typically producing brighter sounds and softer materials producing mellower sounds.
Additionally, the size and shape of the harpsichord's case and soundboard can influence the timbre. Larger instruments typically have a richer, fuller sound than smaller instruments, and instruments with more complex soundboard shapes can produce more complex timbres.
Finally, the player's choice of registration (which stops are drawn) can also affect the timbre of the harpsichord. Different combinations of stops can produce different timbres, from bright and jangly to warm and mellow.