Unwanted noises and loud sounds must be prevented from being transmitted to humans because they generate serious problems in the long term in terms of psychology and physiology. Helmholtz resonators are typically used as passive sound reducers for noise suppression in acoustic systems, such as vehicle exhaust, industry, engine intake manifolds, blowers, and more. It is a simple structure, but its performance is proper for restricting to a narrow band of frequencies due to its geometry. This work presents an adaptive Helmholtz resonator that can continuously change the effective frequency range regarding diverse sound sources. In this way, optimum performance over a constant point is achieved. The system includes a hollow box serving as a Helmholtz resonator, a variable orifice connected to a servomotor, and a controller. The controller receives the sound level and its frequency from the duct via a microphone and then adjusts the orifice area using the servomotor. This simple configuration adjusts the size of the orifice by rotating the butterfly within an effective frequency range based on the sound source characteristics. The experiments demonstrate that sound reduction in frequencies lower than 1000 Hz is achieved effectively, with an approximate decrease of 46%. Moreover, during a test with a pressurized tube connected to an air compressor, the system showed a 30% reduction in sound level. However, at high pressure, the sound level reduction is 6.6%. Additionally, an air horn was tested as a sound source connected to the tube. The unbearable sound level is decreased by 28.5% at a high level of air pressure, although there are no significant differences in pressure.