A fiber optic pressure sensor featuring a cartridge housing having an end that is exposed to the atmosphere, a thin flexible membrane covering the exposed end of the cartridge housing such that the flexible membrane has an exposed side and a protected side. A fiber bundle is disposed within the cartridge housing, featuring a transmitting fiber having a first and second ends. The first end has a polished finish and the second end is coupled to a light source. The fiber bundle also features a multitude of receiving fibers disposed around the transmitting fiber with each receiving fiber having first and second ends where the first ends are also polished. The fiber bundle is disposed within the cartridge housing such that the first end of the transmitting fiber and the first end of each receiving fiber is adjacent to the protected side of the flexible membrane with free space between the first fiber end and the protected side of the flexible membrane. A light sensing means is coupled to second end of said receiving fibers wherein light launched into the transmitting fiber propagates emerges at the polished end, propagates a very short distance in air, and is reflected by the flexible membrane into the receiving fibers, propagates therethrough, and is detected by light sensing means. Upon a change in the atmospheric pressure, pressure waves cause the flexible membrane to distort causing a change in the amount of light reflected by the protected side of the flexible membrane. Thus the intensity of the light coupled into the sensing fibers begins to modulate in relation to the intensity of pressure wave.