Method of adjusting air gap of an electric horn

The method of adjusting the air gap between the pole piece and plunger of an electric horn wherein the horn includes a sheet metal housing of cup configuration having a sidewall and a bottom wall, an electromagnetic coil within the housing adjacent the walls thereof, a pole piece fixed relative to the bottom wall within the coil, a diaphragm mounted upon the housing having a ferromagnetic plunger affixed thereto extending into the coil toward the pole piece, the housing including a diaphragm mounting surface engagable by a mounting surface defined on the diaphragm adjacent its periphery, the pole piece and plunger each including opposed spaced gap surfaces defining an air gap whose dimension determines the horn audible characteristics and electric switch means operated by the plunger to cyclic energize the coil, comprising the steps of measuring the distance from the housing diaphragm mounting surface to the pole piece gap defining surface to obtain a first dimension, measuring the distance from the diaphragm mounting surface to the plunger gap defining surface to obtain a second dimension, determining the difference between said first and second dimensions, deforming the housing to vary said first dimension in accord with the difference between said first and second dimensions whereby upon assembly of the housing and diaphragm a predetermined air gap dimension will result, and assemblying the housing and diaphragm.