A proper fit on your head is important for both comfort and optimal noise reduction performance. Here are some guidelines:
Make your final adjustments with the headset powered on in a noisy environment. In very loud conditions, such as during takeoff, you may experience a brief reduction in noise cancellation as the headset compensates for a momentary pressure change.
A low rumbling sound or frequent brief losses of noise reduction may indicate an improper fit or blocked earbud ports. During a long flight, you may feel a slight pressure point, which can be relieved by adjusting the headband position. Your experience with using the headset will help establish a sense of how it should sound and feel.
Microphone placement is important for clear communications. With the headset on your head, make these adjustments:
Grasp the boom with your fingers and move the microphone up or down so it is level with your mouth
Pull the microphone in toward your lips. Position the microphone with the white mark facing your lips and keep it 1.3 cm from the opening of your lips. It should not touch your lips.
Make sure that you try the headset and test its operation before flying.