There is a huge "literature" on this subject and anyone has his own experiences, opinions and stories to tell.
We'll never know what really works, I mean we'll never know if the fish has come close because attracted by the sound, or if he came close for other reasons. Only the fish could tell, but: 1) he's a fish and can't speak. 2) he's dead, cooked and eaten, so again he cant' speak.
The only scientific notion we have is that fish are very sensitive to vibration: they're more impressed by what they "feel" with their lateral line sense organ, than by what they see with their eyes.
What we don't know, and may only try to guess, is which vibrations are "good vibration" for a fish, and which vibrations scare them away.
1) Generally speaking, I BELIEVE that a spearo's dive should be quiet, stealthy and sleek: the splashy sploshy messy kind of dive does not work with most of the fish.
2) some particular sounds are said to work well to attract some species of fish. Such as:
- a handslap on the water surface seems to attract sea bass (european bass, dicentrarchus labrax), as a well as a "croak croak" sound made with your voice/throat.
I have an explanation for the handslap: it might be similar to the blow of tail from a small fish escaping near the surface. A bass will come close to see if there's a school of bait there. The "croak croak": I don't know what it could mean to a bass...?
- a deep "goo goo" from your inner tongue is said to attract breams (maybe snappers too?), as well as a "clop clop" whipping the foretongue, or a "tickle tickle" made by tickling your teeth. The tickling is quite clear: it's similar to the sound of breams cracking mussels: means food.
- the picking of rubber bands I've heard about by many spearos but God knows what it could mean to a fish.