Energy Conversion Devices was created in 1960.

Sound energy is mechanical energy. No devices are required to make a conversion.

motor

Stanford R. Ovshinsky invented and patented the NiMH battery and founded Ovonic Battery Company in 1982. Ovonic Battery Company is a subsidiary of Energy Conversion Devices, Inc. (NASDAQ: ENER)

Energy conversion I would say means converting say thermal energy to mechanical, or mechanical to electrical, or other conversions you can think of. Now some machines do this, like electrical generators, or electric motors which is the same but in reverse. Other machines are just mechanical, like a gearbox for example, mechanical energy in and mechanical energy out. So the word machine is more general, energy conversion devices are a sub-set of machines.