A broadband noise hybridized with pure tones often occurs in practical engineering work. However, assessments of a
muffler's optimal shape design that would simultaneously overcome a broadband noise hybridized with multiple tones within a constrained space were rarely addressed. In order to promote the best acoustical performance in
mufflers, five kinds of the hybrid
mufflers composed of a
reactive unit, a dissipative unit, and Helmholtz resonator (HR) units will be proposed. Moreover, to strengthen the noise elimination at the pure tone,
mufflers having parallel multiple-sectioned HRs or having multiple HR connections in series (
muffler D and
muffler E) will be also presented in the noise abatement.
On the basis of the plane wave theory, the four-pole system matrix used to evaluate the acoustic performance of a multi-tone hybrid Helmholtz muffler will be presented. A numerical case for eliminating broadband noise hybridized with a pure tone emitted from a machine room using five kinds of mufflers (muffler A-E) will also be introduced. To find the best acoustical performance of a space-constrained muffler, a numerical assessment using a simulated annealing (SA) method is adopted. To verify the availability of the SA optimization, a numerical optimization of muffler A at a pure tone (280 Hz) is exemplified. Before the SA operation can be carried out, the accuracy of the mathematical model will be checked using the experimental data.
The influences of the sound transmission loss (STL) with respect to N1-array HR and the STL with respect to one-array HR sectioned in N2 divisions have also been assessed. Also, the influence of the STL with respect to the design parameters such as the ratio of d1/d2, the diameter of the perforated hole (dH), the porosity (p % ) of the perforated plate, and the outer diameter (d2) of the dissipative unit has been analyzed.
Consequently, a successful approach in eliminating a broadband noise hybridized with a pure tone using optimally shaped hybrid mufflers and a simulated annealing method within a constrained space has been demonstrated.
