These would be set up within a solid, a liquid or a gas due to the vibration of the molecules there. They are transmitted by both intermolecular forces and by collisions between the molecules. In solids they could be either longitudinal or transverse vibrations while in a liquid or a gas only longitudinal vibrations are really possible. Examples of these waves would be the P and S waves in the Earth's crust due to an earthquake and sound waves in air.
These do not require a medium for their
transmission. They are made from an electric and a magnetic field oscillating at right angles
to each other. Examples of these would be light, X rays, ultra violet, microwaves
etc.
Now the pulsing or non-pulsing of your examples.
(a) a singer – this is
a continuous wave train. You can see this by recording the sound of a human voice and
loading into a computer sound analysis program (I have used a good one in England
produced by Cambridge Scientific Media). The vibrato in the voice does not break the wave
train, only change the loudness and maybe the pitch slightly.
(b) an explosion – the
explosion is also a continuous wave train but one of definitely varying amplitude. After the
initial loud sound the amplitude dies away but once again the wave train is not broken (see
the sound analysis program again).
(c) falling dominoes – this is rather like a series of
small explosions as each domino falls over. What I said about the explosion applies to each
domino but the effect of a whole series of them falling over will be to given a broken wave
train and so a series of pulses. These pulses may well overlap. Each time a domino hits the
ground a pulse will be generated and this will die away as time passes.