Before revision:  The other diffusion process comes into play, when the price of the durable is such, that only those consumers with a sufficient personal income can afford the good . We have to distinguish between a monopoly market and a polypoly/oligopoly market. In the first case periodic variations of the total sales occur caused by the initial Bass diffusion, even when the price is constant. In the latter case the mutual competition between the brands leads with time to a decrease of the mean price. Based on an evolutionary approach , it can be shown that the mean price decreases exponentially and the corresponding diffusion process is governed by Gompertz equation (Gompertz diffusion). Most remarkable is that Gibrat's rule of proportionate growth is a direct consequence of the competition between the brands .
After revision:  The other diffusion process comes into play, when the price of the good decreases according to a logistic law. Both, the established unit sales and price evolution are in agreement with the empirical data studied in this paper. The presented approach discusses further the interference of the diffusion process with the supply dynamics .