eeh said:
Hi,
Is it possible to detect sound behind concrete wall or door whereas the
detector is placed outside the room?
Think about this:
There might be noise outside the room, which would overwhelm any sound
from inside, no matter how sensitive or powerful an amplifier you use.
Because the sound coming through the wall from inside the room will be
extremely weak, any little vibration or noise would totally obliterate
it. You need to have a very quiet room to place your detector in.
Through the door would work better, just because the signal from inside
the room is less attenuated.
Now get away from my door.