Learn Dutch: Er is helemaal niemand die de echo hoort. - There is absolutely no one who hears the echo.

The word helemaal literally means 'completely' or 'entirely'. When you put it in front of niemand (no one), it amplifies the negation to mean 'absolutely no one' or 'nobody at all'.

Why do we use die instead of wie for 'who' in this sentence?

When a word like 'who' refers back to someone just mentioned (in this case, niemand), Dutch uses the relative pronoun die. You generally only use wie as a question word ('Who is that?') or after prepositions ('the person to whom...').

Why does the verb hoort go at the very end of the sentence?

The word die introduces a relative clause, which is a type of subclause that gives more information about niemand. In Dutch subclauses, the working verb hoort (hears) is always pushed to the end.

Could I use Daar is instead of Er is to start this sentence?

No, you need Er is here. Er is is used to introduce the general existence of something, matching the English 'There is'. You only use Daar is when pointing to a specific physical location ('Over there is...').