Controlling the transistor requires an intermediate step converting the sound to heat. In my book, this isn't really an 'acoustic' transistor. Phononic transistors have been proposed though[0]. Phononic transistors have been built, albeit with some magnets, but merely for their nonlinear mechanical properties[1]

[0] https://arxiv.org/abs/1509.00679

[1]https://www.pnas.org/content/114/18/4603