Purpose: To evaluate the efficacy of the Duet lithotripter's novel design of two independent spark-plug generator/reflector systems focused at a common F2. The apparatus allows either simultaneous delivery of shockwaves from both generators (resulting in a per-shock energy delivery at F2 equal to that delivered by its single generator at about 24 kV), alternating (between the two generators), or single-generator delivery of shockwaves at various energy levels and rates. Materials and Methods: Eighty-five phantom gypsum stones (volume 786 mm3 each) were placed in a net-like basket and immersed in a specially designed waterbath coupled with the Duet lithotripter (Direx Medical Systems Ltd., Petach Tikva, Israel). Shockwaves were delivered at rates of either 60 or 120 per minute and at intensities of 16 or 22.8 kV (electrohydraulic). Energy was delivered either separately from each generator, in an alternating mode, or simultaneously from both generators. The number of shocks required to fragment the stones sufficiently to allow all of the pieces to fall through the basket holes (complete fragmentation) was recorded. Results: The number of shocks required for complete fragmentation in the alternate mode (120 shocks/min, each generator rate 60/min; 22.8kV) was lower than with the single generator, 112 ± 19 v 134 ± 18 (at a rate of 120/min; 22.8 kV). The simultaneous mode of dual generator shockwave delivery was more effective than the traditional single generator (114 ± 28 shocks at a rate of 120/min, 16 kV v 159 ± 40 shocks at a rate 120/min; 22.8kV). Conclusion: The Duet lithotripter is more effective when used in a simultaneous or alternating mode than is the classical single mode of shock delivery, with the added benefit of shorter treatment time.