The fan generates one acoustic milliwatt of power. The acoustic consultants Bolk, Beranek and Newman recommended it. One acoustic milliwatt of broadband noise in the reverberant room was too loud to talk over. It leads to the question of loudspeaker efficiency. The answer is a theorem for maximum power transmission.
Matched impedances give maximum power transfer.
The speaker cone is a high impedance source. Try sticking your finger through it. The air, on the other hand is very low impedance. It's easy to put your finger through it. Energy transfer, therefore, is very inefficient and we need comparatively high power to the speaker to get the same level as the fan.