Office workers and call center professionals should should always bend the mic boom so the tip is 1-2 finger widths from the corner of your mouth. (This assumes your headset has a bendable noise cancelling microphone.) If the microphone is not in proper position, the noise cancelling technology cannot do its job and your caller will hear everything going on around you. When correctly positioned, significant ambient room noise can be stopped from leaking to your customer. This means shorter calls, less repeats, and you can talk in a lower voice, helping reduce the overall noise level.
How Microphone Noise Cancelling Works
Professional quality office headsets have holes on the front and back of the microphone. Room noise is sampled through the outside hole in the mic (the room side) and it presses on a diaphragm inside the mic and is cancelled out. 
The hole on the inside (the speaking side of the mic) is directional. It picks up sound directly facing it so it must be positioned to always face the mouth. If the mic boom is straight and not bent close to the mouth, it will naturally pick up room noise to your left or to your right, depending on which way it is pointing. Improper microphone position can also cause voice clipping and can make you talk louder.
The hole on inside of the mic must face your mouth, not a neighbor. Strive for 1-2 finger widths from the corner of the mouth, level or just below the lower lip.
Bend the mic to pick up your voice”not the noise around you. Check to be sure the mic is facing your mouth. Adjust throughout the day. Keep the mic 1-2 finger widths from the corner of the mouth. This will ensure the most professional and productive conversations without distracting background noise.
