When mechanical waves have a frequency below the audible range, these are called

Options

A. sonics
B. infrasonics
C. infrasonics
D. supersonics

Explanation

To solve the question, "When mechanical waves have a frequency below the audible range, these are called," we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Concept of Sound**:
- Sound is a type of mechanical wave that travels through a medium (like air, water, or solids).

2. **Defining the Audible Range**:
- The audible range for human hearing is typically between 20 Hz and 20 kHz (20,000 Hz). Frequencies below 20 Hz are not heard by the average human ear.

3. **Identifying the Categories of Sound**:
- Sounds can be categorized based on their frequency:
- **Infrasonic Sound**: Frequencies below 20 Hz.
- **Audible Sound**: Frequencies between 20 Hz and 20 kHz.
- **Ultrasonic Sound**: Frequencies above 20 kHz.

4. **Determining the Answer**:
- Since the question specifically asks for mechanical waves with a frequency below the audible range, we need to identify which category this falls into.
- The category that corresponds to frequencies below 20 Hz is **Infrasonic Sound**.

5. **Final Answer**:
- Therefore, mechanical waves that have a frequency below the audible range are called **Infrasonic Sounds**.