Actually not that true, there were some experiments in the 50s that shown that through bone conduction a human could hear up to 100khz. Likewise, babies hear mu

Actually not that true, there were some experiments in the 50s that shown that through bone conduction a human could hear up to 100khz. Likewise, babies hear much higher frequencies than the "common" 20khz. sources: * https://www.ncbi.nlm.nih.gov/pubmed/10848570 https://www.ncbi.nlm.nih.gov/pubmed/10848570 * https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5285336/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5285336/ * http://asa.scitation.org/doi/full/10.1121/1.2761883 http://asa.scitation.org/doi/full/10.1121/1.2761883