A novel experimental technique is introduced that allows multimode interference and coupling due to boundary topography and to the presence of scatterers in shallow water acoustic waveguides to be studied in the absence of radiation and elastic bottom effects. The air‐suspended water waveguide model consists of a water layer bounded above by air and below by a thin rubber membrane supported by pressurized air to counteract the weight of the water. Experimental data on the transmission of transient ultrasonic signals along the ‘‘perfect’’ waveguide are presented and compared with theory. Both experimental and numerical results are used to demonstrate that multiple nondispersed discrete pulses in a waveguide are equivalent to a summation of highly dispersed waveguide modes. Preliminary experimental results are also given demonstrating the propagation of transient acoustic waves in a free‐fluid layer waveguide with sloped or periodic boundaries.