The aim of this test is to simulate the noise conditions that the spacecraft will experience inside the fairing of the Vega rocket during the Launch.
To simulate the Launcher noise conditions, the spacecraft is put into the "Reverberation" chamber or Acoustic Noise Facility. In here, noise at Levels of over 100dB are generated using compressed air and delivered into the chamber via the massive horns. It's a bit like Standing next to enormous speakers at a nighclub. The chamber is designed to allow the noise to "reverberate" and the response of the spacecraft is measured using a network of accelerometers which measure the motion of the spacecraft due to the noise.