A portable sound-masking device for placing on a roll-up door having a number of horizontally-extending elements. The sound-masking device has a fixture, a magnet, and a transducer. The fixture has an inner face, an outer face, and a pair of spaced-apart tabs protruding from the inner face, the tabs being configured to engage one of the horizontally-extending elements of the roll-up door. The magnet is fastened to the inner face of the fixture and provides a force that tethers the sound-masking device to the roll-up door. The transducer is fastened to the outer face and is configured to emit sound-masking noise.