I think that is actually a base module for what appears to be a surround sound system for your entertainment unit. They are typically hidden away behind sofas or other pieces of furniture for maximum affect, however the inside of a cabinet would be a good place to hide it as well.
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Alan
2012 Ram 3500 DRW Crew Cab, 6.7 HO Cummins
2014 Columbus M-340RK
'69 Chevy C-10, 396BB
Mine was behind a non-opening door under the TV, along with the typical FR rat's nest of wiring. Too bad, I had all intentions of putting in an electric fireplace there. Funny, though the door could have at least had holes in it or a speaker grill, then I could comment on the never ending thumping as it is I never hear it!
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2016 Flagstaff 27VRL Emerald
14K Equalizer
2020 Silverado 2500HD CC 4X4 6.6L gas 3.73