Abstract Typical sound measurements in helicopter cabins indicate that a major contributor to the sound results from airborne transmission of the low-frequency sound (below 400 Hz) created by the main and tail rotors. At these low frequencies, passive acoustic treatments are generally not practical for reducing interior noise, due to size and weight limitations. Results in this paper indicate that active noise control (ANC) systems can provide marked reductions in the low-frequency noise within helicopter cabins. Experimentation was conducted on a helicopter fuselage with an ANC system that consisted of four optimally placed speakers, eleven microphones located in the ceiling trim and an adaptive broadband feedforward controller. The laboratory demonstration showed that the ANC system provided 10-20 dB reduction of the main and tail rotor tones between 40 Hz to 200 Hz. This corresponded to a 3 - 13 dBA overall noise reduction at the passenger head level. Furthermore, noise reductions were spatially global below 80 Hz.
Jolly et al. (Sun,) studied this question.