Eristatakse infraheli (sagedus vähem kui 16 Hz), inimkõrvaga kuuldav heli (16 Hz-20 kHz), ultraheli (20 kHz – 1 GHz) ja hüperheli (üle 1 GHz). Heli levimiskiirus on toatemperatuuril õhus 332 m/s, vees 1490 m/s.
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