China manufacturer of magnetic ballasts for metal halide flood lights & hps flood lights

One characteristic of iron-cored electromagnetic ballast operating at 60 Hz, is the generation of audible noise. Noise can be increased by high temperatures, and it is amplified by certain luminaire designs. The best ballasts use high quality materials and workmanship to reduce noise. Noise is rated A, B, C, or D in decreasing order of preference. An "A" rated ballast will hum softly; a "D" rated ballast will make a loud buzz. The number of ballasts, their sound rating, and the nature of ambient noise in the room determine whether or not a system will create an audible disturbance.

Electromagnetic ballast generate audible noise as a result of magnetically induced mechanical stress. This may be amplified or attenuated depending on fixture design, mounting methods and room acoustics. There are presently no noise standards for HID ballasts. Generally, Single Voltage Hybrid and HX ballasts are noticeably quieter (greater than 10 dB) than CWA, CWI or regulated lag ballasts.