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Explore the Spectrum
Move your cursor across the display to explore sound frequencies — from earthquakes to medical imaging.
Three Categories of Sound
All sound is organized by frequency (how many wave cycles per second). The unit is Hertz (Hz).
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Infrasound
Below 20 Hz Too low for humans to hear
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Audible
20 Hz to 20 kHz What humans can hear
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Ultrasound
Above 20 kHz Too high for humans to hear
Here is the full frequency spectrum from low to high. Each zone blends into the next.
Elephants communicate using infrasound. Normal conversation is audible. Bats navigate using ultrasound. Medical ultrasound is far above even bat frequencies.
Notice the massive jump between audible sound (thousands of Hz) and medical ultrasound (millions of Hz). The "kHz" means thousands. The "MHz" means millions.
SPI EXAM TOPIC
Medical Ultrasound Range
Diagnostic ultrasound uses frequencies between about 2 MHz and 15 MHz. That is millions of cycles per second, far beyond what any human or animal can hear.
Frequency Affects Image Quality
Higher frequency gives better image detail (resolution) but cannot penetrate as deep. Lower frequency penetrates deeper but with less detail. Choosing the right frequency is a core skill in scanning.
Quick Check
The frequency range of human hearing is:
Concept Recall
Diagnostic ultrasound uses frequencies in the range of: