In many industrial environments, room and cavity modes may severely strengthen the annoyance of low frequency noises, such as in ventilation equipments. Moreover, there is an obvious technological gap in the state-of-the-art relative to low-frequency soundproofing, and the only potential solutions basically take the form of heavy and bulky bodies, that can be practically impossible to implement in real situations. With a view to reducing the low-frequency annoyance, in the range of 30 Hz, resulting from the general ventilation system of the CHUV (University Hospital of Vaud Canton) in Lausanne, a prototype of electroacoustic absorber has been developed, consisting of closed-box loudspeakers connected to electric shunt networks, acting as efficient low-frequency sound absorbers. A numerical model has first been developed and challenged with in-situ measurements. Then the electroacoustic absorber design has been optimized, and theoretical performances have been verified. Finally, the prototype has been assessed in situ, both in terms of global acoustic performances, and also in terms of perceptual low frequency annoyances relief, based on the satisfactory analysis of the neighbourhood of the hospital.