Answer: Option 4, increase in wave frequency.
Explanation: As the technician approaches the speakers, he "feels" the waves with a bigger frequency, this is because of the doppler effect.
This happens because his movement is in the opposite direction of the soundwave, and if we step in his point of view, he sees the soundwaves moving faster towards him. This causes an increase in the frequency that he feels, and as we know, as higher is the frequency of a soundwave, higher is the pitch of the soundwave.
so the right option is the 4 one, increase in wave frequency.