Electric power plant noise results from a combination of many sound sources whose spectral composition varies according to the equipment: broadband noises mainly related to cooling towers, tonal emergence noises from e.g. transformers and other noises whose spectrum is located in the middle frequencies. In order to study the impact of industrial noise from a ‘sound design’ point of view, two experiments were conducted. In the first, sixteen stimuli were created by combining cooling tower noise, transformer noise and another source of industrial noise, mixed with two types of background noise (‘nature’ and ‘road traffic’). Via a computer interface, thirty-two people played on the composition of industrial stimuli while keeping the overall level constant at 40 dB(A) to design ‘optimized’ stimuli. Thus, three types of strategies were shared by the participants. The most commonly used strategy involved masking the tonal emergence by broadband noise from the cooling tower. For this group of participants, the increased pleasantness of listening to this optimized stimulus is equivalent to a sound level reduction in the original sound of approximately 3 dB(A). A second group modifies the original sound very little and therefore the increase in pleasantness is almost nil. Finally, only three people, statistically too small for us to deduce any real optimization strategy, tend to reduce broadband noise. In a second experiment, thirty-two new people who had not participated in the optimization phase compared the pleasantness of signals whose broadband component noise level was increased compared to the two others with signals whose three sources were at the same sound level. This second experiment made it possible to find a majority group of listeners who largely prefer the sounds where the broadband component predominates. For a second group of people, the change in the spectral balance, in other words the ‘sound design’, has little effect on the perceived pleasantness, and this is mainly dictated by the overall sound level. Finally, for a single person, increasing the proportion of noise from the cooling towers seems to be detrimental to pleasantness.