In this work, we investigate the Fourier characteristics of wavelength-scanned optical spectrum of low-finesse Fabry-Pérot (FP) acoustic sensor both theoretically and experimentally. The wavelength scanning will transform the time-domain acoustic signal into phase modulation loaded on the FP sensor spectrum distributed along wavelength. Therefore the interference spectrum can be regarded as carrier signal in the wavelength domain. From this perspective, it is intelligible that the phase modulation loaded on the spectrum (carrier signal) will introduce sidebands in Fourier domain. The spatial frequency and phase of sideband components contain unique information of both acoustic signal and the corresponding sensor. These conclusions are experimentally proved by single sensor head as well as two parallel sensors. The Fourier characteristics of sideband components can be utilized to recognize and distinguish acoustic signals received by different sensors, indicating that it has potential applications in multiplexed FP sensor array and source localization, and so forth.