Although hearing aids come in all shapes and sizes, they all have the same basic components. Sound is picked up from the environment by a microphone. The function of the microphone is to change the sound from an acoustic signal to an electronic signal. The electronic signal is then processed and amplified by the hearing aid. The hearing aid volume is adjusted with a volume control.
All hearing aids require a battery to supply power to the system.
Once the sound has been amplified, it goes to a receiver. The receiver works like a speaker changing electronic signals back into acoustic sound. The sound is then delivered to the ear canal through a tube in the earmold or hearing aid shell. Most hearing aids also include on-off switches. These standards require that hearing aids be tested in a sound treated chamber which meets its specifications.