china sports bluetooth wireless earphone supplier

Noise-canceling headphones are designed to reduce or eliminate ambient noise by using active or passive noise cancellation to create a neutral sound environment. This type of headphone has two types – active noise canceling and passive noise blocking. Active noise canceling is achieved by generating reverse sound waves that are equal in amplitude but opposite in phase to the first three or four unlabeled frequencies (for instance, 100Hz and 120Hz), which cause the total amplitude of the combined signal to be minimized when this signal is played back over air. Passive noise reduction relies on a physical barrier between the user's ear and external sounds — such as earmuffs mounted on headphones — to prevent surrounding sounds from entering the ear canals (as opposed to active noise cancellation, which creates an internal sound field that counteracts outside sounds).