I need a device that can send a loud signal/sound through a concrete wall.
This sound should only be hearead at the other side (receiver side). On the sender side it should not be heared.
I will give a reward of 0.2 BTC for a reference where i can get such a device or how i can build it.
What you are looking for is a subwoofer (or 2).
If you want to really piss off your neighbours get some subwoofers and crank up some gangster rap with heavy 808 drums in it or get some heavy dubstep and shake their fucking walls apart.
I have a 10" subwoofer in my room.. and you can hear it outside easily if cranked up a small amount of volume.
BTC address (if I helped): 1Fobj7GfvXSbHshbmxmdSiYTQEtwv8TKeK