You can hear him long before you can see him. In fact finding him is probably the hardest part. We used to joke, "How do you hide something that big?" In breeding grounds only the males sing. They sing the same song over and over. It's about 15-20 minutes long and they come up and take a few breaths in between repeats before diving back down to belt out into oblivion. When you're close you can hear them singing even on board a small boat. The sound waves ricocheting off anything in their way.
We lied down and put our ear against the floor of the deck. We could hear him but we couldn't find him, even when we'd slip in the water and have a look around. His back was the same shade of blue as the water surrounding him so unless you happened to approach his white-sided belly you could easily swim right past him. But suddenly we started to see the outline of his figure engulfed in that same shade of blue. We slowly floated towards him. The last thing we wanted to do was disturb him or spook him away. The sound would deafen the largest subwoofer speaker ever made. You can FEEL the sound. Shaking your entire body. My free diving fins are as long as my legs and I could even feel the very tips of them vibrating. Imagine standing beside a huge speaker at a concert and now multiply it by ten. It's like your bones are rattling inside you. And the tips of your fingers feel tingly.
After floating at the surface for a while we saw that he was pretty unthreatened by us so I slowly swam down to get a closer look. The closer and closer I got down to his head the deeper and louder I could hear and feel his singing. I finally got down to his face and looked at him. And I saw his eye, looking me over slowly, as he kept singing. I just closed my eyes and held my arms out and let myself hang there. It can't fully explain it. It just felt like magic.