Question

Two loudspeakers are about 10 m apart in the front of a large classroom. If either speaker plays a pure tone at a single frequency of 400 Hz, the loudness seems pretty even as you wander around the room, and gradually decreases in volume as you move farther from the speaker. If both speakers then play the same tone together, what do you hear as you wander around the room?

	The sound is louder but maintains the same relative spatial pattern of gradually decreasing volume as you move away from the speakers.
	The pitch of the sound increases to 800 Hz, and the sound is louder but not twice as loud. It is louder closer to the speakers and gradually decreases as you move away from the speakers−except near the back wall, where a slight echo makes the sound louder.
	As you move around the room, some areas seem to be dead spots with very little sound, whereas other spots seem to be louder than with only one speaker.
	The sound is twice as loud−so loud that you cannot hear any difference as you move around the room.
	At points equidistant from both speakers, the sound is twice as loud. In the rest of the room, the sound is the same as if a single speaker were playing.

Answer 1

When both the speakers are played together in phase, due to interference of the two sources, waxing and wanning of sound occurs. The is a maximum intensity region and minimum intensity region in the room.

The sound is louder but maintains the same relative spatial pattern of gradually decreasing volume as you move away from the speakers - wrong - this is variation of intensity with distance and not interference.

The pitch of the sound increases to 800 Hz, and the sound is louder but not twice as loud. It is louder closer to the speakers and gradually decreases as you move away from the speakers−except near the back wall, where a slight echo makes the sound louder - wrong - pitch is not a multipler, same condition above is applicable

As you move around the room, some areas seem to be dead spots with very little sound, whereas other spots seem to be louder than with only one speaker - True - waxing and wanning of sound due to interference. There can maximum intensity and minimum intensity points in the room.

The sound is twice as loud−so loud that you cannot hear any difference as you move around the room - wrong Intensity is not a multiple, its a log adder.

At points equidistant from both speakers, the sound is twice as loud. In the rest of the room, the sound is the same as if a single speaker were playing - wrong - same as above