What is the frequency range of human hearing?

Human hearing range: roughly 20 Hz to 20,000 Hz (20 kHz). The upper limit declines with age (presbycusis) — most adults can't hear above 15-16 kHz by age 40-50. Infants and children have the full range; teenagers can typically hear ringtones around 17-19 kHz that adults cannot. Sound frequency relates to PITCH: low frequencies (low pitch — bass) at 20-250 Hz; mid (voice fundamental, instruments) 250-4000 Hz; high (cymbals, high voice, hi-hat) 4000-20000 Hz. Specific examples: deep bass guitar fundamental ~40-50 Hz; piano ranges 27-4186 Hz (its 88 keys); human speech fundamentals 85-255 Hz (men ~85-180, women ~165-255), with overtones extending much higher; soprano voices reach ~1000+ Hz on top notes; violin ~196-3000+ Hz; piccolo ~600-5000+ Hz. SOUND INTENSITY measured in decibels (dB) — logarithmic scale: 0 dB = threshold of hearing; 20 dB = whisper; 60 dB = conversation; 80 dB = busy traffic; 100 dB = lawn mower; 120 dB = rock concert (pain threshold approached); 140 dB = jet engine (immediate hearing damage). Each 10 dB increase = 10x sound INTENSITY (but only ~2x perceived loudness because of how hearing works). Hearing damage: prolonged exposure above 85 dB causes gradual hearing loss; brief exposure above 140 dB can cause immediate damage. Hearing protection (earplugs, earmuffs) is essential in noisy environments. Sound waves: longitudinal pressure waves in air (or other media). Travel at ~340 m/s in air (varies with temperature, humidity, altitude); 1500 m/s in water; ~5000 m/s in steel. WAVELENGTH = speed / frequency. 1000 Hz sound has wavelength 0.34 m in air. ULTRASOUND: frequencies above 20 kHz, inaudible to humans but heard by some animals (dogs hear to ~45 kHz, bats use 14-100+ kHz for echolocation); medical ultrasound 2-15 MHz; cleaning ultrasound 20-40 kHz. INFRASOUND: frequencies below 20 Hz; produced by earthquakes, large machinery, some animals (elephants and whales communicate with infrasound over long distances).