The continuing power of drone as a combination of soothing and aggressive force -- in whatever balance the creators and, perhaps, the listeners, want -- defines a strain of rock-as-such continually, something Mountains had demonstrated a number of times over their releases prior to Air Museum. But this album perhaps best shows the duo able to capture the sense of drone as exaltation, something derived from the choice of instruments used, whether old keyboards, guitars, effects pedals, or further combinations and extrapolations as desired. That there's a sense of tradition at work is clear enough, the bubbling notes and stretched-out electronic wheeze of the opening "January 17" able to suggest late-'70s space rock obscurities, Pete Kember's mid-'90s explorations, or the dying-cassettes indie rock fascinations of the 2000s and 2010s. "Sequel," the album's centerpiece, not only builds on this uniform feeling but helps send it to a lovely height, the introduction of a calm, steadying melodic loop a couple of minutes into the lush flow of the arrangement turning a fine song into something almost anthemic, something the concluding high-volume wash of "Live at the Triple Door" also achieves to the full, a glorious-sounding reaching out by means of huge feedback swells. Another particular quality of Mountains here lies in their ability to suggest longer songs than are recorded; each piece sounds like the basis of something that could develop in many different directions live rather than one "straight" way of performing it. So if the concentrated synth-pulse rhythm of "Thousand Square" is a direct sort of a hook, hearing the swathes of feedback that growl in the mix halfway throughout or the dizzying sense of distant bird sound is something else, where the stuttering flow of "Blue Lanterns on East Oxford" similarly seems like what could be the starting point for something even more gently mesmerizing.