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Methods are introduced for modeling acoustic signals in reverberant environments. The application considered is stepped-sinusoid testing of underwater electroacoustic transducers in facilities where boundary reflections arrive at the hydrophone before the steady-state response of the transducer under test can be observed directly. The new methods are based on least-squares estimation of parameters in signal models composed of weighted sums of exponential functions. In the first method, only the pre-echo transient response is modeled. In the second method, a multipath model is used to represent the direct signal and the reflections. In addition, a new Prony-type method is introduced for generating initial pole estimates from the pre-echo portion of the response, and model constraints are introduced into the least-squares error functional to allow optimization of the time-of-arrival parameters. The new methods are used to calibrate a low-frequency resonant tonpilz projector in a small pressurized tank. These results are compared to results obtained using conventional methods in a large lake where the echo-free reception time is long enough to directly observe the steady-state response. Excellent agreement is demonstrated.