Covering an air duct vent in an circ. 1900 building

Karin

I live in an old apartment building that still uses steam heat. The ceilings are quite high and near the top of one wall there is the large (1 1/2 x 1 1/2 ft) air duct vent. The problem is that I can hear the upstairs neighbor's t.v. as if it's sitting in my own living room and the noise is coming directly through this vent. I want to know if I can safely cover the vent with a noise reduction material, or if this is going to cause some sort of fire or air quality problem.

Steamhead

Is that

an exhaust duct for ventilation?

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