US Patent 7740104 Multiple resonator attenuating earplug

A non-vented shell earplug for insertion into the ear canal has multiple chambers configured as coupled acoustic resonators. Each chamber is provided with an acoustic element having inertia and resistance coupling the chamber to its neighbor to form multiple resonant chambers. The dimensions of the individual acoustic elements set the frequency response of the earplug, and determine the attenuation characteristics of the resonators. Unlike the single chamber resonator of the prior art, the multiple-resonator earplug provides attenuation in both low and high frequency segments of the noise spectrum.