The intermittent exhaust noise(IEN)generation mechanism during the compressed air spraying from cylinder of pneumatic frictional clutch through pneumatic valve is discussed. The sound source distribution of the exhaust noise is analyzed based on the aerodynamics. Considering the existing pressure shockwave in the airflow

the concept of shockwave impulse acoustic source is proposed. The acoustic source

compared with ones at the other position in exhaust system

achieves the maximum strength to IEN

and then is located at the outlet. A relation of the acoustic source with both mass flux and flow speed at the exhaust outlet is set up. With the radiation characteristic of the piston acoustic source instead of that of the shockwave impulse acoustic source

the formula for calculating its sound pressure(SP)and sound pressure level(SPL)is presented. A comparison between the analytical results and the experimental results shows that their SPLs on 1/1 octave spectrum are in good agreement

with the average error less than 5%. Both the pressure shockwave and the impulse characteristic of the sound source result in the intermittent exhaust noise with much great high-frequency content

which provides the theoretical foundation for designing mufflers to reduce intermittent exhaust noise of pneumatic frictional clutch in mechanic press and for diagnosing faults in exhaust process.