The synthesizer, the Theremin, and the electronic organ are totally electronic
instruments. They don't make any sound at all without electronic circuits and
electric power.
The acoustic guitar is not inherently an electronic instrument. It can be made
louder with microphones, and given special effects with other electronic stuff.
Whether any of this is actually an 'enhancement' is open to debate.
Answer:
Starting from the beginning.
There is a radio signal that is received by the radio.
The radio interprets the signal and produces a current in response to it.
That current goes to a membrane that oscillates producing sound, the oscillation of the membrane is the first mechanical energy event here.
These oscillations can travel in material mediums, for example, the air. Then there is a production of waves (soundwaves) that travel in the air (second event).
Those waves now hit the wall that separates you and your neighbor, as the wall is made of a material, the soundwaves can travel through it, but they will be dispersed (a part of the waves rebounds on the wall, and another part is dissipated as the wave travels through the wall), there is also a transmitted part of the wave, that is now in your house. (this change of medium will be the third event). Now only the lower frequencies survive, this is why the sound is "muffled".
Those remaining frequencies now travel in your house, and when they reach your ear, your ear sends a signal to your brain and your brain interprets them as sound. The wave interacting with your ear will be the fourth and last mechanical energy event.
Unable to be noticed or not felt because of feeling slight
Answer:
The slope of a graph of position vs time
