Two identical audio speakers connected to the same amplifier produce in-phase sound waves with a single frequency that can be varied between 300 and 600 Hz. The speed of sound is 340 m/s. You find that where you are standing, you hear minimum-intensity sound.

(a) Explain why you hear minimum-intensity sound.

(b) If one of the speakers is moved 39.8 cm toward you, the sound you hear has maximum intensity. What is the frequency of the sound?

(c) How much closer to you from the position in part (b) must the speaker be moved to the next position where you hear maximum intensity?