This work deals with the energy pumping phenomenon for acoustical applications. The concept of energy pumping is to passively reduce the vibrations of a primary system by attaching to it an essentially nonlinear damped oscillator also named Nonlinear Energy Sink (NES) creating a strongly nonlinear coupling which localizes and dissipates the vibrational energy. In the context of acoustics, a vibroacoustic coupling is used. In an earlier work, we showed experimentally that a loudspeaker used as a Suspended Piston (SP) working outside its range of linearity can be used as a NES. In this work, the performance and efficiency of a SP NES is studied numerically and experimentally. The considered acoustic medium is a resonant pipe. The coupling between the pipe and the NES is ensured acoustically by a small acoustic compliance (the air in a coupling box). Various observed aspects of energy pumping are presented: behavior under sinusoidal forcing, pumping threshold, resonance capture and transient response. As a SP NES technology permits an easy control of the moving mass of the NES, the effect of this parameter is also studied.