This restricts the limits of human hearing.

The idea

Human hearing runs from about 20 Hz to 20 kHz. The conversion of sound waves to vibrations of solids works over a limited frequency range. The ceiling exists because the structures within the ear, such as the ear drum and ossicles, cannot vibrate fast enough to detect higher frequencies. Sounds above the upper limit are ultrasound and those below the lower limit are infrasound. The range of human hearing narrows with age, with the top end falling first. Prolonged exposure to loud noise can also damage the ear and raise the minimum sound level a person can detect, particularly at high frequencies. Exam questions may ask students to interpret graphs showing how the minimum audible level changes with age and noise exposure.

What earns the marks

• Stating the range of normal human hearing as 20 Hz to 20 kHz.
• Explaining that the limits of human hearing are restricted because the solid structures in the ear only vibrate over a limited frequency range.
• Saying the minimum sound level that can be heard increases with age.
• Saying that working in a loud environment raises the minimum level detectable, particularly at higher frequencies.

Common mistakes and how to put them right

• Saying sounds above 20 kHz do not exist, instead of saying humans cannot detect them.

• Confusing the upper limit of human hearing (20,000 Hz) with the lower limit (20 Hz).

• Reading a hearing graph as loudness rather than as the quietest sound that can just be heard.

Exam tips

• Learn 20 Hz and 20 kHz as a pair, and convert the upper limit to 20 000 Hz when a calculation needs consistent units.
• Use the phrase minimum sound level that can be heard rather than volume when reading audibility graphs.
• Remember that the conversion of sound waves to vibrations of solids only works over a limited frequency range.