Optimization of composites used in sound insulation in split type outdoor unit system with theory, modelling and experimental result

Noise reduction strategies play a critical role in enhancing the acoustic performance of heating, ventilation, and air conditioning systems (HVAC) directly influencing user satisfaction. This study explores advanced experimental and modeling methodologies to optimize multilayered soundproofing composites for use in split-type outdoor air conditioning units. Measurements were conducted in a full anechoic chamber to ensure precision and eliminate environmental interference. A comparative analysis of four composite configurations was performed, focusing on their material properties and structural designs. Results indicate that optimizing both the compressor operating frequency and the composite layering significantly improves noise reduction. The best performance was observed at 100 Hz compressor frequency using a five-layer hybrid composite, achieving an overall sound pressure level of 46.6 dB(A). Notably, tonal peaks such as the third harmonic at 325 Hz were eliminated following compressor frequency adjustment. In the high-frequency range, the five-layer S4 structure provided up to 4.9 dB additional SPL reduction at 5460 Hz. These findings confirm that a dual-domain approach which includes mechanical tuning of the compressor and acoustic engineering of multilayer composites can achieve perceptually significant improvements in HVAC noise performance. The proposed configuration is retrofit-compatible and was developed in direct response to a real-world tonal noise complaint, highlighting its practical applicability. This study demonstrates the effectiveness of integrated experimental and modeling approaches for practical and theoretical advancements in HVAC acoustics.