I’d recommend basing your design off the Type 2 Electromechanical Horn design.
Below are some animated GIFs I made a while back showing different methods of making electromechanical horns.
Type 1 Horn:
Examples: Federal Vibratone 350, Faraday 5720, 5740, Simplex 4030, 4040, 4050, Edwards AdaptaHorns
Type 2 Horn:
Examples: Federal Vibratone 450 (Series A & B), Simplex 4041, 2901-9806, Wheelock 31, 34, 31T, 34T, 7001, 7002, 7001T, 7002T, 7004, 7004T, Amseco BZ-series
Type 2 Horn (Faraday version):
Examples: Federal Vibratone 450 (Series C), Simplex 2901-9833, 2901-9838, 2901-9840, 2901-9845, 2901-9846, Faraday 4120, 5920, 5940, 6020, 6040, 6120, 6140
Type 3 Horn:
Examples: Federal Vibratone 450 (Series D), Simplex 4901, 4903 series, Faraday 6230 – 6258, Siemens / Cerberus Pyrotronics U-HN, U-NH, U-HNH, Gentex GMS / GMH