Some of the things you would discover would include that in some locations the voices don't show up. Investigating that, you would find that deep in caves they were gone. If you had access to the materials radios are made from, you would discover that in a metal box the voices don't show up. You would infer from this that the voices are coming from outside and are somehow picked up by the box. You might also discover by putting pieces of radios together differently that you could get your own voice to come out of the speaker by hooking up two speakers in series with the power source.

My point is that you would learn a lot more about what is really going on then this long quote suggests.