The authors have measured the rates of ultrasonic B-mode speckle pattern changes as a function of the change in center frequency of the transmitted acoustical pulse under a variety of experimental conditions. Experimental results agree with a previous theoretical description of this phenomenon. The results are used to determine the optimal method of frequency compounding for speckle reduction in a fixed bandwidth imaging. The analysis indicates that by dividing the available system bandwidth in half for the purpose of frequency compounding, the equivalent of 1. 46 independent images may be averaged for speckle reduction. Further analysis indicates that frequency compounding does not improve diffuse target detectability in a fixed bandwidth system.