A high gain quantum cascade terahertz (THz) sound-laser (SASER) device was designed and fabricated using principles inspired by THz optical quantum cascade lasers. In this acoustic device, phonons are generated by driving current pulses through the highly ordered superlattice structure. The superlattice structure is designed to utilise inversely populated intersubband electron transitions to achieve high acoustic phonon generation efficiency. High performance was achieved by systematically scaling a 1.2 THz superlattice structure to 700 GHz. The high-intensity phonons were confirmed using superconducting bolometers on-axis, i.e. directly opposite the SASER device, and off-axis (0.5 mm away from the SASER device). The detected phonon intensity on-axis was observed to increase with applied current above a threshold at a faster rate than the increase of power dissipated in the device, while the intensity measured off-axis decreased. This observed collimation of the phonon emission provides strong evidence for stimulated phonon emission.