Part of the Web Audio API is a convolver node, which adds a reverb effect. This might be better known as echo, or actually the opposite too... you can use it to make audio sound like it's in a big concert hall, or under water, or in a tiny basement.
It works by multiplying a waveform to the main audio track. One problem I always find with this is 'what waveform?' - which one should I be using to create different effects?
I came across these free files from cksde.com. So thought I would make a page which demos what each one sounds like. Just press play and select which ever file.
Surprisingly this webpage makes noise - fair warning.