Answer
These "antinoise" devices are discussed on page 385. They play a mirror-image version of the jackhammer noise into the operator's ears, and the superposition of the 2 waves at the operator's ears causes the 2 sounds to cancel out. The greatly reduced jackhammer noise allows the operator to easily hear you.
On the other hand, you do not enjoy this antinoise technology, and loud jackhammer dominates the sound of the operators' voice.
