In order to reduce the loudness of a sound we have to

Options

A. decrease its frequency of vibration of the sound
B. increase its frequency of vibration of the sound.
C. decrease its amplitude of vibration of the sound.
D. increase its amplitude of vibration of the sound.

Answer

To solve the question "In order to reduce the loudness of a sound we have to," we will analyze the properties of sound, particularly focusing on loudness and its relationship with amplitude and frequency.

### Step-by-Step Solution:

1. **Understand Loudness**:
- Loudness is a measure of how strong or intense a sound is perceived by the human ear. It is a subjective perception that can vary from person to person.

**Hint**: Remember that loudness is related to how we perceive sound, not just the physical properties of sound waves.

2. **Identify Factors Affecting Loudness**:
- Loudness primarily depends on the amplitude of the sound wave. The amplitude is the maximum displacement of the wave from its rest position.

**Hint**: Think of amplitude as the height of the sound wave; higher waves are louder.

3. **Understand the Role of Amplitude**:
- The greater the amplitude of a sound wave, the louder the sound will be. Conversely, a smaller amplitude results in a quieter sound.

**Hint**: Visualize sound waves; larger waves mean more energy and thus more loudness.

4. **Consider the Role of Frequency**:
- Frequency, which determines the pitch of the sound, does not affect loudness. Loudness is independent of frequency.

**Hint**: Remember that pitch is how high or low a sound is, while loudness is about how strong the sound is.

5. **Conclusion**:
- To reduce the loudness of a sound, we need to decrease its amplitude. This means making the sound wave smaller in height.

**Final Answer**: To reduce the loudness of a sound, we have to **decrease its amplitude**.

### Summary of the Answer:
- The correct option is to **decrease the amplitude** of the vibration of the sound.