An engineer measures the dominant frequency of the sound produced by three sources in air.
| Source | Frequency | Classification |
|---|---|---|
| motion sensor | 35 kHz35\ \text{kHz}35 kHz | |
| ventilation fan | 14 Hz | |
| alarm | 1.6 kHz1.6\ \text{kHz}1.6 kHz |
Classify the sound from each source as infrasound, audible sound or ultrasound. Write your answers in the table.