Piano acoustics
Piano acoustics is the set of physical properties of the piano that affect its sound. It is an area of study within musical acoustics.
Multiple strings[edit]
All but the lowest notes of a piano have multiple strings tuned to the same frequency. The notes with two strings are called bichords, and those with three strings are called trichords. These allow the piano to have a loud attack with a fast decay but a long sustain in the attack-decay-sustain-release (ADSR) system.
The trichords create a coupled oscillator with three normal modes (with two polarizations each). Since the strings are only weakly coupled, the normal modes have imperceptibly different frequencies. But they transfer their vibrational energy to the sounding board at significantly different rates.
The normal mode in which the three strings oscillate together is most efficient at transferring energy since all three strings pull in the same direction at the same time. It sounds loud, but decays quickly. This normal mode is responsible for the rapid staccato "Attack" part of the note.
In the other two normal modes, strings do not all pull together, e.g., one pulls up while the other two pull down. There is a slow transfer of energy to the sounding board, generating a soft but near-constant sustain.[4]