A characteristic of the piano tones is their double decay (the initial sound followed by the "aftersound"), related to the existence of two polarizations. The goal of this study is to understand and to compare more quantitatively than the previous work, the influence of parameters which are under the control of the piano tuners: the mistuning and irregularities in striking action of the hammer. We simulated on a computer the vibration of an unison group of strings, which includes the dominant damping at the bridge as well as the vertical coupling between strings. Excitation irregularities were simulated by varying the initial deplacement and velocities of the strings. The study analyses the ratio of the aftersound to the immediate sound, the compound decay, and the amount of destructive interference. This interference can be seen where the slope of the decay curve changes, and is most pronounced at the bridge, where the strings are dynamically coupled. This comparison leads to the conclusion that if necessary, the piano tuner can to a certain extent correct for a poorly adjusted hammer by modifiying the mistuning. But all hammers properly adjusted are essential for a constant and uniform level for all notes, which is necessary for a very good piano.