Contradiction? Not quite – allow me to explain.
Echo is indeed the operative word here, since Thergothon's only album proper (from 1992) is very nearly as ambient as metal gets. Dominated by long, slow guitar lines, heavy on the reverb, like Sabbath in treacle, notes are left hanging in the air before the music drags itself forward one more step. On some songs, the guitarist seems to be tuning up for several minutes before a riff emerges from the gloom.
Underneath this, growling vocals are interspersed with chanting and whispering, all indecipherable, Lovecraft-inspired. Occasional 'atmospheric' interventions from what sounds like a child's Casio keyboard induce a feeling of mild narm. Somewhere in the background, the drums plod on with barely a hint of swing. The tinny production actively hinders any usual feeling of metal awe.
And yet taken as a whole, Stream... makes for an accessible avant-garde smash. It's doom metal in love with the hum of the amplifier, crude fragments of electric blues and folk rising out of the murk. It's drone metal with songs. The lo-fi production's tendency to undercut the ambition of the record strips it of pomposity, rendering it oddly endearing.
The album spawned a new micro-genre in its wake: funereal doom metal, although what I've heard of its offspring so far suggests that there was something magical in the original production and throwing money at the sound quality just takes it away and gives you something far more orthodox (and therefore considerably less interesting).
However, it's also not too big a jump further out and forward in time from Thergothon to beatless, decidely less song-oriented acts like Sunn O))) . Keep the pace down but tighten up the playing, add in a smattering of jazz and blues, and then you've got late-period Earth, circa The Bees Made Honey In The Lion's Skull.
It might be a misreading of metal history, but I hope it's a strong one. For me Stream... sits much more readily in that progressive tradition than Sabbath played at half speed with an extra dollop of misery. But its both a ground-breaking and love(craft)able piece of work in its own right.