You have to rip out everything and then you cut into the steel with an oxy-fuel torch, then you place a shaped charge into the cut.  They usually remove any non load bearing walls too.   You can't just put the shaped charges on top of someone's desk and expect the building to come down because the explosive force would follow path of least resistance.    In the debris after a controlled demolition, you would find thousands of blasting caps and miles of detcord wire (WTC 7 had 1.8 million square feet.  There's a ton of evidence left over. http://s.hswstatic.com/gif/building-implosion-20.jpg The high explosives used to cut steel are insanely loud too.  If you make them quieter, you make them less powerful.  You can't explosively cut steel and keep it quiet.  There's a direct relationship because both are based on the air pressure generated when exploding.