Speed of sound.. if i am travelling at 1/2 the speed of sound, and there are sounds coming from behind me and in front of me. i understand they will sound at different frequencies to me, but will i still detect them as both travelling at the same speed?

If they were beams of light, then you'd see both beams pass you at
the "speed of light", no matter what your own speed happened to be,
and no matter what the speed of the sources happened to be.

But since they're beams of sound, The sound from the source behind you
will pass you at 0.5 times the "speed of sound", and the one from the source
in front of you will pass you at 1.5 times the "speed of sound".

Multiply the 3 dimensions, assuming it is a rectangular cuboid, to get the volume in cm³ divide mass by volume to get density in g/cm³