It is a simple stethoscope based on a Greman design I found here. I managed to improve it for my purposes and gain a greater amplification, however at the expense of increased circuit noise. Nevertheless, the whole prototype may work as a simulator for introducing the concept of noise vaccination (desensitisation to sounds of a certain loudness, which in practice means decreasing human hearing sensitivity). By adjusting the potentiometer in the middle, one can see how silence might look like after the vaccination, where on this scale is normal human hearing sensitivity and how loud to a person before the treatment might become vaccinated person's normal sound intensity level.
