all that's required is a pair or more, relatively high energy hypersonic beams targeted at windows in the building, at slightly different frequencies the sum or difference of which would be at a super-audio frequency. Persons would be unable to hear the beat frequency, yet would be affected by it. This might be a side-effect of what used to be used to listen to what audio information was being generated in the building.

I've got no evidence of this, though I do know a laser bounced off a window could be used to eavesdrop on the people in the room with that window.

RE