Most broadband Tonpilz transducers are achieved by coupling first-order longitudinal mode with other modes introduced by an elaborately designed structure (e.g., flexural mode of the head mass). To further expand the bandwidth is difficult and, even if successful, inevitably makes the structure more complex. Longitudinal modes are the inherent vibration modes of rod-shaped Tonpilz transducers. Using high-order longitudinal modes to achieve broadband performance can retain the simple structure similar to the conventional Tonpilz transducer. However, activating continuous, equal-amplitude longitudinal modes is not easy. The longitudinal length and position of the drive-stacks have significant influences on the generation of resonances and their vibration amplitude. In this paper, these influences are studied using the equivalent circuit method for a rod transducer having two drive-stacks, and finally we provide the drive-stack arrangement that can activate the first-three longitudinal modes to obtain the desired broadband response effectively. We also find that the response value of resonances can be balanced to reduce band fluctuation by adjusting drive lengths. The design procedure for the broadband Tonpilz transducer is proposed. The finite element method is used to design broadband transducers having bandwidth greater than one octave following the procedure. A transducer prototype with a simple structure is fabricated and measured to verify the validity of the proposed method.