Yeah, that's what puzzles me.  Infrasonics' amplitude would have to be so ridiculously high that you'd knock the building down, first.  Ultrasonics would, in theory, get blocked, but you can't pinpoint the effect with EM.

The localization of the effect would be dependent on the wavelength (frequency), which is also what made me think it had to be ultrasonic.  In thinking about it more, you'd have to have three sources of audio generation, or you'd have multiple affected zones.

This one's got me stumped.