The human ear normally works by trapping sound waves travelling through the air, amplifying them and turning them into signals the brain can understand. But bone conduction sends the waves through the skull bones or jaw instead, bypassing the natural air conduction system. In normal hearing patients, bone conduction is an unnecessary phenomenon and as a component of physiological hearing compared to air conduction is weaker by about 50-60 dB. Bone conduction transmission can be used in individuals with normal or impaired hearing. Bone conduction technology has long been used in hearing aids for the hearing impaired, but also in specialized communication products (e.g. in high-noise environments, or underwater) in normal hearing. Another phenomenon – sound vibrations – can be felt in the body (face and hands) as well as being detected in the ear. Vibratometry is a one of audiological method used for registration of sound vibrations feeling by bone conduction.