After conquering a few mental fears equalisation is normally the biggest obstacle that most spearfishers will encounter.
The reason we need to equalise is because it bloody hurts you if you don’t. How’s that for a good enough reason?
Seriously, hydrostatic pressure (10m ocean depth is equivalent to 1 mile high in the sky. We take approximately 10 seconds to arrive at 10m). That’s why we need to equalise. As you descend the water pressure increases hence the pressure increases inside your ear canal, hurting your tympanic membrane (ear drum) – you have to “equalise” this outside pressure by matching it with air pressure that you have inside you. Equalising maintains pressure balance between the middle ear space, the rest of the body and surrounding water. The Eustachian tube comes into play here, this tube runs from the back of your nose to the air space of the middle ear. The tube is generally collapsed, opening when the “clearing” (equalising) process eventuates. When you experience the “crackle, pop” sounds you are equalising, relieving the pressure on the Tympanic membrane and sinus cavities. Correct technique and equalising before you experience discomfort is the key to comfortable spearfishing, and ensuring there is no chronic damage to your eardrums.