Life, much like television, is very rarely at the right volume. When there’s not too much noise for you to concentrate, there’s some soft-talker saying God knows what while you struggle to keep up. Once the latter problem becomes too prevalent it might be time to look into hearing aids. But for the former there are Knops, ear plugs that act as a kind of universal volume control system.
Knops, are, incredibly, intended to be worn inside your ears all the time. Assuming there are people who would actually do this, users have access to three different levels of acoustical, rather than electrical, volume control. The first level is more or less normal sound, passed to your ears without modification. Level two cancels out ambient background noise, like that which you would experience in a large city. Three takes it up a notch, reducing a loud concert or other noise-heavy environment to a quieter volume level, while four basically puts you inside a completely silent force field.