Abstract: The present disclosure discloses an acoustic device and a method for determining a transfer function thereof. The acoustic device includes a sound production unit, a first detector, a processor, and a fixing structure. The sound production unit is configured to generate a first sound signal based on a noise reduction control signal. The first detector is configured to obtain a first residual signal including a residual noise signal formed by superposition of an environmental noise and the first sound signal at a location of the first detector. The processor is configured to estimate a second residual signal at a target spatial location that is closer to the ear canal than the first detector, and update the noise reduction control signal based on the second residual signal. The fixing structure is configured to place the acoustic device at a location near a user's ear but not blocking the ear canal.