This paper reports a tunable acoustic notch filter utilizing a Helmholtz resonator (HR) array. Passive acoustic filters based on mechanical resonators have the advantages of no power supply requirement; however, the filtering frequency is not adjustable compared to active noise control. The proposed device consists of three-layered parts: cavities, a membrane, and microchannels. The cavities work as HR chambers, which determine the resonant frequency. Due to the HR effect, the acoustic wave is effectively insulated at the frequency. The HR chamber volume can be changed by deforming the membrane with air pressure through the microchannels. Thus, it enables adjustment of the resonant frequency, realizing a tunable acoustic notch filter. The prototype device realized the frequency tuning approximately from 4 to 5 kHz with 10 dB filtering. Thus, it can handle a wide range of high-frequency noises that humans tend to find uncomfortable.