Yeah, I don’t know, I suspect you’re right. I know that 25 years ago there were big flat speakers thay drove sound with little holes. Those things could only handle high ends despite being very large themselves. But I know that with DSP you can treat an array of microphones as a single microphone, and the diameter of the array sort of dictates the size of the microphone. Speakers and mics tend to sort of be opposites, in that you can drive or be driven by either. For years I’ve wanted to build a wall of cheap speakers and experiment with this. I suspect I’d find out what we already know, which is to get deep frequencies you have to move a lot of air, and an array of small piezos can never move a lot of air…

That said, it might matter a lot what the substrait was. If it was light and flexible, you could maybe get all the piezos to move it in a way to get a very deep frequency. You could probably get deeper frequncies than the power output of the piezos by taking advantage of the resonance frequency of the material. But you’d be stuck with that one frequency, and there’d be a tradeoff in response time