They also help reduce background noise, such as that from air conditioners, street activity, echoes, and footsteps. (artbusinessnews.com)
I suspect this has something to do with Dynamic De-Noise, a function that OnePlus says reduces background noise in post-processing. (techradar.com)
Its front - facing bottom grill projected music the right way - forward - not down at the ground, and its four microphones for voice calls and noise canceling reduced background noise to appropriate levels in all our test calls. (techradar.com)