The high level of noise in helicopter cabins considerably compromises the comfort and safety of the pilot and passengers. To verify the feasibility and effectiveness of microperforated panel composite sound absorption structures for noise suppression in helicopter cabins, simulation and experimental studies were conducted on a model of a light helicopter cabin. First, three microperforated composite sound absorption structures for the helicopter cabin wall panel were designed. Then, a finite element model of the main gear/body acoustic vibration coupling was established to obtain the target frequencies of the microperforated composite sound absorption structures; the acoustic effect was verified via simulation. Finally, a model helicopter cabin equipped with the three microperforated composite sound absorption structures was built, and a cabin noise test was performed. The test results showed that the combined microperforated panel acoustic structure and microperforated panel–porous material composite structure realized an overall cabin sound pressure level attenuation of 8–10 dB, on average, in a wide frequency range of 500–2000 Hz, with an amplitude of more than 20 dB. The microperforated panel–acoustic supermaterial composite structure achieved low-frequency sound absorption in the frequency range of 300–450 Hz. The sound absorption effect reached 50%, and it also exhibited good noise reduction effects in the middle- and high-frequency bands.

The structure-borne tones generated by the main gearbox are the primary components of helicopter interior noise. Recently, a kind of periodic strut has been designed to isolate the multispectral vibration from transmitting to the cabin, for their specific stop-band characteristics. Using multicell optimization, the disorders are designed into the strut to obtain better vibration and noise reduction effect. The dynamic model of the periodic strut is firstly established by combining the spectral element method and the transfer matrix method. On this basis, a multi-objective multivariable genetic algorithm is adopted to optimize the geometry by taking the maximum attenuation as the performance objective function. Then, a near-periodic structure is achieved. Compared with the perfect periodic strut, the optimal one has a much wider and deeper stop band, which is critical for a better vibration and noise attenuation effect. In addition, a method is presented to analyze the wave propagation to explore the increase of width and depth of the bandgaps more closely. Experimental investigations are then carried out on a pair of original and optimal struts to validate the improvements. It is shown that 26.22% more attenuation is achieved through this structural optimization.