Abstract: An electromagnetic signal horn of a type including a housing, a membrane whose peripheral edge is attached to the housing and which with the housing defines a chamber, an electromagnetic motor arranged in the chamber, and a magnetic core arranged in the chamber with an attaching pin thereof extending through a central opening of the membrane, with a coupling channel thereof, for coupling the chamber with outside atmosphere, being partially defined by a radial recess at the central opening of the membrane, wherein the central opening is four-sided, or square, for simplifying and economizing its fabrication, with a spacing between opposite sides of the central opening being the same, or only slightly larger than, a diameter of the attaching pin.