Teacher sheet · Ages 15–16 · about 45–50 minutes
Hearing: transduction, timing and noise dose
Lesson page: echoesof.science/school/ears/ages-15-16/ · Pupil worksheet: echoesof.science/school/ears/ages-15-16/print/
Learning aims
- Describe the mechanics of the middle and inner ear, including the frequency map of the basilar membrane.
- Explain mechanoelectrical transduction in hair cells.
- Calculate interaural time differences.
- Distinguish conductive and sensorineural hearing loss.
- Plan a survey, calculate mean and range, and evaluate uncertainty.
Lesson plan
| Time | Activity |
|---|---|
| 5 min | Starter: why do sounds seem to come from inside your head with headphones? |
| 10 min | Read the text and work through the time-difference calculation. |
| 20 min | Noise survey in groups (or two places only, as a demonstration). |
| 5 min | Pool the results; discuss mean, range and app reliability. |
| 5 min | Quiz, or the Conductive or sensorineural? game as homework. |
Materials for the experiment
- A phone or tablet with a free sound-level-meter app (one per group)
- A map of the school
- A metre stick or tape measure
Safety: Do not go near loud machinery or traffic to take readings. Never put a device or earphones close to anyone's ear. If a place is uncomfortably loud, take the reading and leave.
Common misconceptions
| Pupils may think… | Actually… |
|---|---|
| The eardrum turns sound into nerve signals. | Hair cells in the cochlea do the transduction; the eardrum and ossicles only pass on and amplify the vibration. |
| Only very loud bangs damage hearing. | Moderate levels for long times, e.g. 85 dB for hours, can also damage hearing. |
| Hearing aids fix every kind of hearing loss. | They mainly help conductive loss; cochlear implants are an option for some sensorineural loss. |
Worksheet answers
- Different places on the basilar membrane vibrate most for different frequencies: the stiff, narrow base for high frequencies (10,000 Hz) and the floppy apex for low frequencies (200 Hz); hair cells at each place signal that frequency.
- Δt = 0.20 / 340 ≈ 0.00059 s ≈ 0.59 ms.
- Group results; a sound answer compares the mean with 70 and 85 dB, considers how long people stay there and notes the range.
- Uncalibrated microphone, the device's position and distance, background changes between readings; reduced by a fixed method and three repeats.
Quiz answers
- Which part of the basilar membrane responds best to high frequencies? The stiff, narrow base. Stiffness and width change along the membrane, giving a frequency map.[2]
- For a sound at one side, the extra path to the far ear is 0.17 m and v = 340 m/s. The time difference is… 0.5 ms. Δt = 0.17 / 340 = 0.0005 s = 0.5 ms.[4]
- Which cells are the main auditory receptors? About 3,500 inner hair cells. Outer hair cells mainly fine-tune the response.[2]
- Hearing aids usually help most with… conductive hearing loss. Sensorineural loss is not treated by amplifying sound.[3]
- Why is noise-induced hearing loss permanent? Cochlear hair cells cannot grow back. Loud sound can kill hair cells, which are not replaced.[6]
- According to CDC, a motorcycle at 95 dB can damage hearing after about… 50 minutes. The louder the sound, the shorter the safe time.[5]
Going further
Research how a cochlear implant uses the frequency map of the cochlea: why does it need many electrodes along its length?
Sources used in this lesson
- [1] How Do We Hear? (National Institute on Deafness and Other Communication Disorders (NIDCD, NIH)): reliability High
- [2] Biology 2e, 36.4 Hearing and Vestibular Sensation (OpenStax, Rice University): reliability High
- [3] Psychology 2e, 5.4 Hearing (OpenStax, Rice University): reliability High
- [4] Sensation and Perception: Interaural Time Difference (University of Minnesota (open course text, PSY 3031)): reliability Medium-high
- [5] What Noises Cause Hearing Loss? (Centers for Disease Control and Prevention (CDC)): reliability High
- [6] Hearing and Hair Cells (Stanford Medicine, Ear Institute): reliability High
- [7] Deafness and hearing loss (fact sheet) (World Health Organization (WHO)): reliability High
Full list with links and a note on each source's reliability: echoesof.science/school/ears/sources/
Privacy: the lesson pages have no ads, no tracking and no cookies. Quiz answers and game scores stay in the pupil's browser. A short video for each age is coming.