I suppose it could be capturing EM emissions from the printers rather than acoustic, but that would make it fundamentally more like the other TEMPEST hacks as a way to exploit unintentional emissions, rather than as a sneaky covert channel where you have control over the computer equipment, but don't have access to external interfaces to offload your stolen data.
Unless I'm misunderstanding some part of your description, anyway.
I suppose it could be capturing EM emissions from the printers rather than acoustic, but that would make it fundamentally more like the other TEMPEST hacks as a way to exploit unintentional emissions, rather than as a sneaky covert channel where you have control over the computer equipment, but don't have access to external interfaces to offload your stolen data.
Unless I'm misunderstanding some part of your description, anyway.