For grating-feedback extended-cavity diode laser (ECDL) whose output frequency is susceptible to environmental interference, with two channel feedback loops for grating and injection current, the frequency stabilization system based on modulation-free polarization spectroscopy is optimized. Its resonant frequency is extended to 155 kHz. The laser frequency fluctuation caused by low frequency random disturbance under open loop is greatly suppressed. It can be suppressed to 1/13570 at 120 Hz. Now that laser frequency fluctuation near the atomic transition center frequency can be measured by use of the polarization spectra, and the acoustic response characteristics of ECDL are depicted experimentally with the analysis of laser frequency fluctuation and sound stimulant signal. By contrasting the acoustic response characteristics of ECDL with or without the soundproofing case, the sound insulating effect could be mapped directly. Experiment results show that sound insulating effect resulted from different frequency can deteriorate from 12.8 to 0.14. The measurement of insulating effect can also act as the experimental criteria for optimizing the design of laser mechanical structures and sound insulation systems. Furthermore,this system could be helpful for the development of acoustic precise measurement.