Small linear phase changes introduced in a uniform linear array of point sources do not cause any appreciable change in the energy radiated until the phase variation along the line becomes equal to that which occurs in the wave in space. Then the efficiency begins to drop rapidly. The efficiency will, of course, be a periodic function of the phase shift. If the excitation of the point sources is due to regularly recurring pulses whose timing varies linearly along the array then the phase variation will be directly proportional to the frequency of the different components. This sort of excitation may be made to occur in paper mill suction rolls. (These are hollow cylindrical shells which are perforated with a pattern of holes through which water is drawn from the paper by means of stationary suction boxes.) Models in which the phase between adjacent holes is varied by the use of different drill patterns have been studied for arrays of sources one foot and 20 feet long. The experiments agree qualitatively with theory on all points and indicate that a noise reduction of at least 15 db can be obtained by choice of a suitable drill pattern.