A hermetic reciprocating freon compressor was instrumented for noise transmission path identification. A mix of force gages, pressure transducers, and an accelerometer were installed to identify the main transmission paths. Triaxial force gages were installed and calibrated to measure the three forces transmitted from each suspension spring to the shell. The three triaxial force gages, along with a pressure transducer measuring the dynamic pressure inside the shell, were used in a multiple reference frequency response function (FRF) analysis with the sound pressure from an external microphone as the reference output. The multiple reference FRF analysis indicates that the suspension springs are the dominant noise transmission path in this compressor.

A scanning laser velocimeter was used to measure the operating shape of one of the compressor harmonic responses. This harmonic shape was interesting because it is a significant sound radiator at a frequency well below the first structural mode identified by both experimental modal and finite element model analysis. The vibration pattern appears to be a combination of rigid-body motion of the compressor shell in response to the orbiting spring forces and a circumferential acoustic mode inside the shell. The sound intensity pattern radiated by a regular version of the same compressor model closely resembles the vibration pattern driven by the rigid-body motion. This indicates that the spring forces actually drive the sound radiation at this frequency.