ADJ.
below, equal, known
VERB + HZ
sounds
HZ + NOUN
infrasound
noun
Initialism of habitable zone.
Initialism of herpes zoster.
noun — the unit of frequency
The tuning note A4 is equal to 440 Hz.
At the other end of the spectrum are very low-frequency sounds (below 20 Hz), known as infrasound.
When your dog tilts his head to listen to seemingly imaginary sounds, he is tuning in to ultrasonic frequencies, as high as 45,000 Hz.