This paper presents preliminary results from study of a magnetostrictive energy harvesting transducer. The magnetostrictive samples studied in the device were 1/4" diameter and 2" long cylindrical rods of commercially available Terfenol-D and research-grade specimens of a new ductile Iron-Gallium alloy known as Galfenol. The transducer design was motivated by interest in harvesting low frequency vibration energy with a target of optimal performance at 50 Hz. The transducer was designed to facilitate study of the sensitivity of magnetostrictive transduction performance to prestress loads in the range of 1 to 4 ksi and DC magnetic biases of from 0 to 300 Oe. Transducer performance was assessed by measuring the open circuit voltage produced by the harvester when it was excited by a mechanical shaker at force levels of 1-4 pound force and at frequencies of up to 100 Hz using both single frequency and swept sine operational modes. The performance comparisons consist of open circuit induced voltage output as a function of prestress and magnetic bias for both Terfenol-D and research grade Galfenol and open circuit induced voltage as a function of frequency and mechanical excitation at biases optimized for different prestress conditions. Scalability tests show how electrical output varies with mechanical input for the two materials under the different operating conditions. The electrical output for operation with Terfenol-D and Galfenol under the same mechanical force inputs are presented and observations of the differences associated with the performance of these two materials are discussed.