There is an anechoic chamber at the University of Salford and it is the closest you can get to hearing absolute silence. It is so quiet, in fact, that you can hear the sounds your body makes, like the blood circulating in your head or a high-pitched hiss, which is thought to be caused by spontaneous activity in the auditory nerve fibres within your brain.
The rooms are used for carrying out acoustic tests such as measuring the performance of ear plugs, loudspeakers and microphones.
They are made so quiet by having multiple walls to stop noise getting in from outside. Like a modern concert hall, the Salford chamber is mounted on springs to prevent vibration entering the inner sanctum. If you talk in the room your voice sounds odd, and very muffled, like listening in an aircraft when your ears need to pop. The walls, floor and ceiling are covered in vast wedges of grey foam which absorb the sound reflections you would otherwise hear from the chamber’s surfaces.
This is a room that can be seen but not heard. Add the claustrophobic drama of being enclosed behind three heavy doors and this can get too much for some people who feel uneasy and ask to leave.