Question

sounds below 20 hz are considered and sounds above 20,000 hz are known as

Explanation:

Infrasound refers to sound waves with frequencies below 20 Hz. Ultrasound refers to sound waves with frequencies above 20,000 Hz. Radiology is related to medical imaging (e.g., X - rays, CT scans) and has no relation to sound frequency categorization. Audiology is the study of hearing, balance, and related disorders, but it does not specifically name the sound frequency categories in the question.

Answer:

Sounds below 20 Hz: infrasound; Sounds above 20,000 Hz: ultrasound.