The coil is located in the magnetic circuit consisting of a permanent magnet, an iron core, a high permeable metal disk, and a vibrating diaphragm.
The disk and diaphragm are attracted to the core by the magnetic field . When an oscillating signal is moved through the coil, it produces a fluctuating magnetic field which vibrates the diaphragm at a frequency of the drive signal. Thus, sound is produced relative to the frequency applied.
The sound producing devices like our sound transducers are generally used in certain enclourse to have an appropriate resonance chamber in front of the sound producing device, it is possible to meet the requirements to a certain extent, for instance, to obtain an increased sound pressure, improved response in wider range of frequencies, or softened sound output. Design such resonator called “Helmholtz Resonator" according to the following equation :