High-frequency drivers need far less motion than low-frequency drivers to radiate similar loudness.

Evidence

The acceleration has a prefactor of f2, the square of the frequency—a strong effect at high frequencies. Low frequencies correspond to slow accelerations, which has to be compensated by large amplitude A to make the sound loud. This is why you can see a subwoofer move (or at least look fuzzy), while a tweeter looks perfectly stationary as it beams sound. The tweeter may be moving microns or even less. — Eric J. Heller, Why You Hear What You Hear- An…, 667

Categorization

• CANDY: The tweeter-vs-subwoofer visual is a fun, tweetable observation about why you can see one speaker cone moving and not the other.