Tenney develops a new definition of timbre fencing off/in opposition to Ohm's in this text. He portrays timbre as a physical phenomenon based on three main parameters: spectrum (frequencies, bandwiths, amplitudes), quasi steady-state modulation processes (frequency and amplitude modulation) and certain transient phenomena. He describes a further 15 subparameters and follows this with a simplified definition that includes all main and subparameters.
Die physikalischen Korrelate der Klangfarbe (The physical correlates of timbre)
Tenney, James C.
Gravesaner Blätter 26: 103-109.