A calorimetric method and apparatus for evaluating transducer assemblies

The essential element of this acoustic flow calorimeter for power transducers is a long lossy line that matches and absorbs the output of the transducer. The line consists of many small, tinned copper tubes, cast into a cylinder of lead. This cylinder is centered in a larger encasing copper tube through which cooling water flows. From water flow rate and difference of input and output temperatures, acoustic power is obtained. Calibration is effected by a heater element bonded to the outer tube. The assembly is in an evacuated chamber. A typical calorimeter for a 15-kHz transducer has an absorbent element 1.25 inch (3.2 cm) in diameter, and 5 feet (1.5 m) long. Results are quite consistent.