|“||That place was where our voices go for their final rest. When there is no one left alive to remember their sound. And now (they are lost)...All our history is destroyed.||”|
|— Ryn about the Echo chamber[src]|
Echo Chamber was a special place deep underwater, in which only few mermaid healers are able to enter. It was the source of the healing song, which neutralizes the effects of the Siren Song. It contained voices of the Merfolk ancestors.
Tia blew up the Echo Chamber with explosives, as she plans on using the Siren Song as a weapon against humans. Hence, she removed the only viable cure to the siren song effects.
In The Toll Of The Sea, it is revealed that Yura's tribe in Alaska have their own Echo Chamber, which was used to neutralize Tia's weaponized song. This likely means there are possibly more Echo Chambers around the world, but how many is not yet known.