"... I do recall, fo example, that USound has developed a...

"... I do recall, fo example, that USound has developed a microchip - that was a couple of years ago!..."

I think you will find that, although USound has developed a MEMS speaker, it is not a digital device. It is an analogue speaker and requires DAC and amplifier circuitry when outputting from a digital source.

On the other hand, the AudioPixels speaker is purely digital. A such, it requires no DAC or amplifier circuitry and has other benefits of small form factor, low power usage and claimed very accurate sound reproduction with almost no distortion.

USound has products that consist of more than one speaker type, e.g. their Proteus 1 model.




On the other hand, AudioPixels is developing a single speaker type that can be deployed singly or in an array of identical speakers, depending on the required performance.