We propose and demonstrate the use of a pair of detuned acoustic resonators to efficiently absorb narrow-band sound waves in a terminated waveguide. The suggested configuration is relatively simple and advantageous for usage at low frequencies, since the dimensions of the resonators are very small compared to the wavelength. We present a theoretical description based on lumped parameters to calculate the absorption coefficient, which agrees very well with experimental data. The experimental results verify that the anechoic (reflection approximately $-38\mathrm{dB}$) narrow-band ($\mathrm{\Delta }f/f\sim 0.1$) termination with deeply subwavelength ($<\lambda /10$) sizes can be realized at a target frequency, suggesting thereby applications for noise control and sensing. As an illustration of possible applications for sound absorption in a room, we demonstrate by use of numerical simulations that a given axial resonant excitation in a room can be practically eliminated. Thus, a reduction of approximately 24 dB in the average acoustic energy is achieved in the room when using only four Helmholtz resonators. We also discuss various scenarios of noise control in rooms.

• Received 3 March 2016

DOI:https://doi.org/10.1103/PhysRevApplied.6.054021