Distributed sensing using all-fiber laser-based acoustic sensors has been demonstrated recently for large area sensing. However, the sensitivity of this type of sensor has so far been much lower by comparison with currently available optical microphones. This paper studies the use of controlled interaction between the modes of oscillation in a fiber laser to enhance the sensitivity of acoustic wave detection. The responses of individual longitudinal modes to acoustic waves in a dual-wavelength fiber laser are demonstrated. With the experimental setup that has been developed, observation of a single wavelength output from the dual-wavelength laser shows optical responses to acoustic waves at 23 dB below the triggering threshold of laser dynamics, when compared with the previous scheme based on uncontrolled multimode operation.