Multi-tone noise elimination in a space-constrained room lined with hybrid sound absorbers using a particle swarm method

High noise levels can be harmful to workers and lead to psychological and physiological ailments. A broadband noise hybridized with multiple pure tones has a high peak value and is detrimental to human hearing in an enclosed machine room. To efficiently reduce the reverberant part of the peak noise level, interest in shape optimization of a Helmholtz resonator attached to the internal wall is coming to the forefront. Research on Helmholtz resonators in dealing with a pure tone has been well-addressed. However, the development of a hybrid sound absorber used in simultaneously reducing both the pure tone and the broadband noise is rare. Therefore, we propose two kinds of hybrid sound absorbers (sound absorber A: a piece of perforate plate + a piece of sound absorbing material + air space + a Helmholtz resonator; sound absorber B: a piece of perforate plate + a piece of sound absorbing material + air space + two Helmholtz resonators) used to deal with a broadband noise hybridized with multiple tones. Here, two case studies for dealing with broadband noise hybridized with one tone and two tones will be introduced. Moreover, a numerical assessment of a sound absorption coefficient and the best optimized design for two kinds of hybrid sound absorbers under a space-constrained situation will be performed. Consequently, a successful approach in eliminating a broadband noise hybridized with multiple tones by using an optimally shaped hybrid sound absorber as well as a particle swarm method within a constrained space has been demonstrated.