Basically the earth emits low frequency sounds which have a unique signature when passing through oil that can be detected on the surface. (wexboy.wordpress.com)
They further established the computational processes by which neurons «tuned» to process low frequency sound actually improve the phase - locking precision of the impulses they receive. (sciencedaily.com)
But, I feel that the speaker lacks depth when producing low frequency sound. (techtree.com)