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The mock-up of a great passive silencer used for noise attenuation in industrial applications has been designed and tested in laboratory. This mock-up consists of three metal casing containing the noise source and several removable rails and supports, allowing the test of different configurations of parallel absorbing baffles. The output of the silencer radiates in an anechoic chamber in order to simulate free-field conditions. The acoustic attenuation has been measured not only at the output, but also inside the silencer, with a mobile microphone located at several positions along the axis. Also, the tested configurations include three types of absorbing pillows and several geometrical arrangements. The results show that the maximum insertion loss (dB) measured at the output of the silencer corresponds to frequencies between 800Hz and 2.5kHz and its value strongly depends on the air gaps between baffles. The measurements with the mobile microphone show a linear decrease of the sound pressure level with t...