Experiment

On the Previous, we explained that the properties of sound waves vary with frequency. Here, we compare sound waves, which have similar properties to radio waves, to see how they differ.

Experiment①　

Method

1. Place the microphone 25 meters away from the speaker.
2. Play sounds of 250Hz and 2500Hz from the speakers at the same volume respectively.

250Hz　※Pay attention to the volume.




2500Hz　※Pay attention to the volume.

3. Observe the sound waves with a microphone and compare which waveform's amplitude is larger.

Result

• 250Hz

  

• 2500Hz

  

As you can see, the higher frequencies (2500 Hz) are quieter than the lower frequencies (250 Hz).

Experiment②

Method

1. Place the speaker and microphone across the door.
2. With the door closed, play 250Hz and 2500Hz sounds from the speakers at the same volume.
3. Observe the sound waves with a microphone and compare which waveform's amplitude is larger.

Result

• 250Hz

  

• 2500Hz

  

In this way, we can see that the sound across the door is smaller at a higher frequency (2500 Hz) than at a lower frequency (250 Hz).

Consideration

These experiments confirmed that low-frequency sounds reach farther and pass through obstacles more easily than high-frequency sounds.

The results of this experiment also apply to radio waves: the "millimeter waves" used in 5G are higher frequencies, which make it harder for radio waves to reach farther and more likely to be blocked by obstructions, so base stations must be placed at narrow intervals.