| CPC H04R 1/023 (2013.01) [H04R 9/025 (2013.01); H04R 9/06 (2013.01); H04R 2400/11 (2013.01)] | 16 Claims |

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1. A front cover structure, applied to a sounder and made of sheet metal, wherein the front cover structure comprises a protrusion portion in middle of the front cover structure, an extension plate extending outward from an edge of the protrusion portion, and an assembly ring provided at an outer edge of the extension plate and surrounding a periphery of the protrusion portion, wherein the protrusion portion, the extension plate, and the assembly ring define an avoiding cavity; a sound hole communicating with the avoiding cavity is formed in the protrusion portion; and the assembly ring is formed by superimposing at least two layers each made of the sheet metal; wherein the assembly ring has a width between 0.4 mm and 0.5 mm, and a thickness between 0.3 mm and 0.36 mm.
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9. A sounder, comprising:
a frame with an accommodating space;
a magnetic circuit unit fixed in the accommodating space of the frame;
a vibration unit fixed to the frame and spaced apart from the magnetic circuit unit, wherein the vibration unit is driven by the magnetic circuit unit to vibrate; and
a front cover structure covering the frame and the vibration unit,
wherein the front cover structure is made of sheet metal and comprises a protrusion portion in middle of the front cover structure, an extension plate extending outward from an edge of the protrusion portion, and an assembly ring provided at an outer edge of the extension plate and surrounding a periphery of the protrusion portion, wherein the protrusion portion, the extension plate and the assembly ring define an avoiding cavity; a sound hole communicating with the avoiding cavity is formed in the protrusion portion; and the assembly ring is formed by superimposing at least two layers each made of the sheet metal; and
wherein the protrusion portion, the extension plate, the assembly ring, and the vibration unit define a front cavity; wherein the assembly ring has a width between 0.4 mm and 0.5 mm, and a thickness between 0.3 mm and 0.36 mm.
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