Hi again and thank you for your replies.
The stair is the entrance of a neoclassical building and it consists of 7 steps.
There is a carpet which can hide the understructure (electronics, wire etc)
The width of each step is approx 1meter. I was thinking of the Laser beam with photoresist's across
but it would be difficult to hide the electronics because again there is not an option to intervene with
the architecture of the building
The question about how this would function is good. Ideally it should be able to send signals to Arduino
(and then from Arduino to RaspberryPi to synthesise sound). I would say that not more than three people would step on the same step probably but it could go also more minimal and sense only one person per step.
How can I expand the area a FSR can detect force on?
I hope I provided some help..