Assessing human hearing
This practical allows you to explore some of the qualities of our sense of hearing and its usefulness to us. It also allows you to begin to consider what the consequences could be of impairment of hearing – by damage to the hearing system or through the natural aging process.
This could be set up as a circus of activities, or small groups could become expert on one task and feed results back to the rest of the group. Or you could use each activity separately as a series of starters or plenaries.
Apparatus and Chemicals
For each group of students:
Sheets of card or stiff paper
Strips of cloth that can be used as blindfolds
For the class – set up by technician/ teacher:
Signal generator able to generate tones from below 20 Hz to above 20 kHz (Note 1)
Rubber/ plastic tubing (1-3 m long) with funnels attached at each end – small (5-8 cm diameter) at one end, large (20-30 cm diameter) at the other, 2 per working group
Yogurt pot shakers with dried beans/ peas (1 per group) and 4 or 5 similar pots with no beanse
Health & Safety and Technical notes
Ensure blindfolded students remain seated
1 Many signal generators in educational suppliers brochures do not cover the full range needed. Free tone generator software is available to download in several places – including from NCH software. Some of your students may have an app for their phones which generates tones. Teachers cannot hear ring-tones at high pitches audible to students. There is an app called Tapstereo available from itunes for a very low price which certainly generates tones at the top end needed, but may not go low enough to be inaudible (itunes.apple.com).
Be aware of any known hearing impairments within the group. Describe the sensitivity of our hearing as variable from one individual to another. React appropriately if students notice any hearing loss of their own for the first time during the course of the practical work. There are many causes of temporary hearing impairment, so issues encountered in the lesson are worth following up but may not be the sign of a long-term problem.
SAFETY: Ensure blindfolded students remain seated at all times.
a Set up the signal generator and try it out to find a suitable volume for tones across the frequency range. Be aware that you will not hear tones at the top end of the frequency range that are audible to your students.
b (Optional) Make a set of yogurt pot shakers – 3 or 4 pots, with only one containing beans.
c Set up the tubing with funnels on each end.
Investigation 1: Highest and lowest
d Run the signal generator from low tones to high tones and note the frequencies at which each individual stops being able to hear the tone.
e Run the signal generator from high tones to low tones and note the frequencies at which each individual starts hearing a high-pitched tone, and then the low frequency at which tones become inaudible again.
Investigation 2: All the better to hear you with?
f Try to focus on one sound in a complicated noise. To do this, you could ask several students to talk at once and get the listener to focus on what one individual is saying. Or have several devices playing music and ask the listener to pick out a particular tune. Or have several students shaking yogurt pots while talking, with only one of the pots containing beans to make a noise.
g Construct conical earflaps from stiff paper or card. Attach them behind your earflaps using string, elastic bands or tape (or simply hold them in place). Evaluate their effect on your hearing.
h Try to focus on one sound in a complicated noise using the extra big earflap. Does it help if you point the earflap in different directions?
Investigation 3: Using your ears to work out where a sound is coming from
i Blindfold a volunteer who will stay seated.
j Make a noise at various points around the room and ask students to point towards the noise when they are able to use both ears, and with one ear covered.
k Ask the volunteer to hold the small-funnel end of the listening tubes over their ears. Make a noise from the same point of the room, but move the big-funnel ends of the tubes to different positions relative to the noise. Note where students think the noise is coming from in each situation.
It is worth distinguishing the ‘earflap’ or pinna (the external flap surrounding the ear canal) from the ‘ear’ which is the organ that detects sound. Most of the functional parts of the ear are in the middle ear (the bones connecting the ear drum to the cochlea) or in the inner ear (the cochlea itself with its sensitive hairs).
Although many exam specifications do not require students to know the names of the parts of the middle and inner ear, students may be interested to know more about how our sense of hearing works.
Health & Safety checked, September 2010
Download the student sheet Assessing human hearing with questions and answers.
Website for the charitable organisation formerly known as the Royal National Institute for the Deaf – now Action on Hearing Loss. If you need more information about hearing loss, or communication strategies for people who are deaf or hard of hearing, this website is useful. The RNID offer a free package for raising dead awareness that includes information about finger-spelling on a poster, bookmark and card, a communications tips card, and leaflets about sign language and people who are deaf or hard of hearing.
The University of Wisconsin hearing loss sampler which provides a series of audio clips demonstrating progressive hearing loss of different types.
Part of the Phonak website. Phonak are a commercial company producing hearing aids. The ‘Hear the world’ site includes a place where you can test your own hearing.
A not-for-profit US-based organisation with an interest in educating the public about the problem of hearing loss. Their simulations cover mild and moderate hearing loss in a variety of situations and simulate hearing speech, music and other sounds.
(Websites accessed October 2011)