Sound Wave
Light, Sound and Waves

Quantifying and using sound - Teaching approaches

Classroom Activity for 14-16

A Teaching Approach is both a source of advice and an activity that respects both the physics narrative and the teaching and learning issues for a topic.

The following set of resources is not an exhaustive selection, rather it seeks to exemplify. In general there are already many activities available online; you'll want to select from these wisely, and to assemble and evolve your own repertoire that is matched to the needs of your class and the equipment/resources to hand. We hope that the collection here will enable you to think about your own selection process, considering both the physics narrative and the topic-specific teaching and learning issues.

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Pitch and frequency - an activity

Sound Wave
Light, Sound and Waves

Pitch and frequency - an activity

Classroom Activity for 11-14

What the Activity is for

The aim here is to bring together the concepts of pitch and frequency. Pupils are encouraged to relate what they hear (high and low pitched sounds) to more precise measurements of high and low frequency.

What to Prepare

  • various pairs of sounds: these might be recorded onto a small music player. You'll need to be able to jump from sound to sound pretty smartly. Most should be a pure note – a single frequency. Some of the pairs of sounds should be very close in frequency; others more clearly separated. For the sake of clarity of demonstration it is probably best not to have the same computer playing the music and analysing it.
  • three cards marked pitch higher, pitch lower, and same pitch: can't tell.
  • three cards marked frequency higher, frequency lower, and same frequency: can't tell.
  • a microphone linked to a computer running sound-analysis software.

The software should produce a near full-screen display like this (Audacity (on Windows, Linux or Mac OSX) currently offers the required facility and more for free).

What Happens During this Activity

Start with pairs of sounds. Play the first one and ask the pupils to indicate with the pitch cards whether the second sound is of higher, or lower or the same pitch.

We think it a really good idea to draw on a wide range of sounds, not just, for example, using musical instruments or the human voice.

Then introduce the computer display, showing how the rise and fall in pitch is matched by the rise and fall in the frequency display. Refer to the numbers up the vertical scale as values of frequency.

To introduce the idea of frequency, go back to counting the to and fro motion of the wobble board. Carefully move through one complete cycle: from the board being as close to you as possible to as far away as possible and then back to as close as possible again. Then introduce the frequency as the number of to and fro movements each second.

Now introduce the frequency cards, asking pupils to make judgements about pairs of sounds in terms of frequency and seeing how they match with the display.

To take it further: plenty of fun can be had with pitch-bending software, which alters the playback rate. This can be used to reinforce the connection between the number of to and fro motions a second and the pitch. Before computers you would have played tape recordings speeded up. Beware of cleverly designed software that alters the rate of playback without altering the pitch: lots of mathematical processing goes into that!

Teacher: The sound we can hear comes from lots of to and fro movements of the speaker and the air each second. There are too many for us to count, so we get the computer to do the counting for us.

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Range of hearing

Frequency
Light, Sound and Waves

Range of hearing

Classroom Activity for 5-11 11-14

What the Activity is for

Exploring the audible range.

The aim of this activity is to reinforce the relationship between pitch and frequency, and to give some feeling for the numbers involved when measuring frequencies. Measuring something about themselves also allows children to make real connections to the topic.

What to Prepare

  • A computer running software that allows you generate and play back different frequencies. In all cases pure notes of a single frequency are best.

What Happens During this Activity

Play back a note of audible frequency and loudness. Ask the class to put their hand up if they hear the note. Now move progressively to higher and higher frequencies. Instruct the pupils to keep their hands raised until they can no longer hear the sound. In this way it is possible to identify the upper threshold of frequency response of the ear and the variation in this figure between members of the class. Repeat the procedure for the lower frequency threshold, moving down through the frequency scale.

At the upper end of the spectrum you might want to turn down the loudness control so that there is actually no sound! This little trick will weed out those pupils who are a little too enthusiastic in their claims. You might even want to discuss using this approach to make the findings of the demonstration more reliable. It has parallels with placebo testing in medicine.

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Seeing and hearing spectra

Sound Wave
Light, Sound and Waves

Seeing and hearing spectra

Classroom Activity for 11-14

What the Activity is for

Building sounds from a range of frequencies.

This activity allows you to introduce the idea that most sounds are made up of many frequencies, and this provides us with a very powerful way of describing and identifying sounds.

What to Prepare

  • a prepared selection of sounds, either recorded with the means to replay them, or a selection of devices to make the sounds
  • a microphone, linked to a computer, running sound analysis software

What Happens During this Activity

Few sounds consist of one pure note. In fact what we hear as a pure note is a very special kind of vibration – it varies sinusoidally (following a smooth sine curve) with time.

First invite pupils to listen to the sounds, then ask them to see, on the screen, what frequencies they are made of.

You might like to draw the parallel with seeing a range of colours and seeing how these are made up from the different spectral colours.

As the different sounds come up, note the different soundprints that could be used to identify the sounds.

In looking at a selection you'll want pupils to notice:

  • The balance between low and high frequencies and how this relates to the pitch they hear.
  • That you can hear two notes at once, making sense of many different frequencies arriving all at the same time.
  • Changes in loudness and how these are recognised.

Such soundprints are the basis of voice recognition techniques.

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Agreeing on loudness

Sound Wave
Light, Sound and Waves

Agreeing on loudness

Classroom Activity for 11-14

What the Activity is for

The aim of this activity is to make the link between the loudness of a sound and the magnitude of the vibration that produces it. The louder the sound, the bigger the vibration (the bigger the amplitude of vibration). The decibel scale is then introduced as a standard scale for measuring loudness.

What to Prepare

  • a wobble board
  • a selection of pre-recorded sounds, or the means for making them. You will need to be able to alter the loudness of the sound.
  • a laser beam, reflecting from a strip of plastic mirror stuck to a vibrating loudspeaker. Make sure the reflected beam has a safe path to a distant wall.
  • an oscilloscope, or computer-based oscilloscope, connected to a microphone, with the time-base switched off.
  • a decibel meter, preferably linked to a large display.

Safety note: Lasers approved for school use should be used. Ensure that the beam cannot enter anyone's eye either directly or by reflection. A laser pointer can be used under the careful control of a teacher but be aware that some are marked with an incorrect power rating and so are more hazardous than they might appear.

What Happens During this Activity

Start with the wobble board, keeping the frequency the same, but driving the board into larger vibrations. Make the connection between this extra movement and a louder sound. You may need to practice this.

Now use the loudspeaker and laser beam to make the link between the amount of movement of the loudspeaker cone (shown by the movement of the laser dot on the wall) and the loudness of the sound. As you turn up the loudness control, the laser beam will move back and forth over a greater distance on the wall.

You can then use the microphone and oscilloscope to show the increase in amplitude on the screen as the sound gets louder. Play louder and softer sounds into the scope and watch the size of the vibrations increase and decrease.

Finally, introduce the decibel scale by demonstrating how a large decibel meter can be used to measure the loudness of the sounds. It is a good idea to demonstrate the link to decrease in loudness as you move further from the source. Also make connections between your readings taken in the lab and common values between the 0 dB threshold of hearing and the 140 dB threshold of pain.

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Tracking loudness

Sound Wave
Light, Sound and Waves

Tracking loudness

Classroom Activity for 5-11 11-14

What the Activity is for

A story told with decibels.

This emphasises the graph as a story about something and a way of communicating. It is an opportunity to increase pupils' familiarity with the decibel scale.

What to Prepare

  • Portable dataloggers with sound sensors (You'll ideally need a number of portable dataloggers with the ability to see what you have captured, fitted with microphones and rigged to measure loudness in decibels. Failing this you can record the sound using any device, then feed it into such a datalogger later. However, this will only reliably give relative values, thus undermining a part of the purpose of the exercise.)

What Happens During this Activity

  • Challenge the class to find an event where the sound level varies in an interesting way.
  • They should log the sound from this event, then tell the story of one aspect of the soundscape using a graph.
  • They should be allowed full access to graphical analysis and annotation tools, so that the computer does more than plot the graph. The final product should tell an interesting story.

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Measuring distance with sound

Sound Wave
Light, Sound and Waves

Measuring distance with sound

Classroom Activity for 5-11 11-14

What the Activity is for

Timing echoes.

A widespread activity is to make a rough measurement of the speed of sound by timing the gap between making a sound and hearing an echo from a wall at a measured distance.

This activity takes things the other way around by assuming the speed of sound (340 metre / second), measuring the time the sound takes and thereby finding the distance that the sound travelled.

What to Prepare

  • A sonic ruler (These are available from many hardware stores. When working it should emit an audible click and then report the distance to the object you pointed it at.)
  • An outside wall, about 150 m away from where the pupils can stand
  • A stopwatch, accurate to 0.01 s

What Happens During this Activity

Start with the sonic ruler and ask if anybody knows how it works. Point out that it seems to be able to measure how far away an object is, simply by bouncing a sound off it. Ask how this is possible. The ruler actually measures the time that a sound pulse takes to travel to and from the object, then finds the distance by multiplying half the round-trip time (out and back) by the speed that it has it has stored in its memory.

If necessary, revise the relationship between speed, distance and time with simple examples.

The next activity takes the class outside. The challenge is for the pupils to find their distance from the wall using the known speed of sound (340 metre / second) and half the round trip time that they measure. Different groups of pupils will need varying amounts of help in carrying out this activity:

  • Stand about 150 m in front of the wall.
  • Make a loud sound (maybe clapping two blocks of wood together).
  • Time how long it takes to hear the echo from the wall.
  • Calculate the distance.

It's good fun to run this activity as a competition. It is also a good place to think about the possible uncertainties in this experiment – beware of those who get suspiciously close to the correct result. How reliable are they as witnesses? This can lead to lively discussion!

This activity offers the opportunity to make connections to the technique of remote sensing. For example, radar mapping of a planet is done in exactly the same way. Times are measured for radar signals to travel to and from the planet, then distances of the surface from the satellite are calculated, thereby giving the height profile of the surface. A number of impressive images, developed by remote sensing, are available on the internet. (See, for example, the NASA site.)

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Sound unwanted

Sound Wave
Light, Sound and Waves

Sound unwanted

Classroom Activity for 11-14

What the Activity is for

Reducing sound reaching a detector.

This activity introduces shielding from sound. Here you need to make sure that children can apply the ideas of reflection and absorption to sound, as well as appreciating the reduction in loudness due to spreading out over larger and larger volumes when transmitted. All three of these can be used to plan for reducing the level of sound reaching a detector.

What to Prepare

  • a small loudspeaker as a sound source, together with a selection of recorded noises to drive it
  • a decibel meter
  • a selection of absorbers and reflectors
  • the interactive object (see below), computer and data projector

What Happens During this Activity

You might start by pointing out that sound often gets where it is not wanted or is much too loud. We are sure the class will be able to provide several examples. You might even brainstorm these, seeking to divide them into situations where people might control the loudness of the sound, and others where they might manage to remove the sound altogether.

Then you might introduce the ways in which sound can be controlled. Once you have set aside reducing the quantity of vibration produced by the source, and reiterated that the vibrations are travelling, point out that you can seek to reduce the loudness of the sound in three ways – by being farther away, so just allowing it to spread out, by hiding behind a reflector, and by hiding behind an absorber.

It is very important that the loudspeaker is isolated from the decibel meter so that the only simple path for the sound to follow is through the air. Beware of unwanted reflections (for example from the experimenters!) Getting valid and reliable results is hard (because of the need to eliminate other paths and background noise – imagine a class of children working all at once), so this is not an easy experiment to give to children as an investigation.

Resources

Download the interactive for this activity.

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Questions to check understanding

Sound Wave
Light, Sound and Waves

Questions to check understanding: sound

Diagnostic Questions for 11-14

What the Activity is for

These diagnostic questions can be used to check the pupils' understanding of sound.

What to Prepare

  • print out the question sheets provided (see below)

What Happens During this Activity

The questions might be used for homework or as the basis for discussion in the class.

Glass Case question commentary: Sounds travel through a gas and bigger vibrations will just make the sound louder and therefore easier to hear. A vacuum contains no particles and therefore cannot act as a medium for sound. It is possible that the rate of vibration is too low for you to hear.

Sound Chain question commentary: You are already equipped with a detector, probably a pair of them. Therefore a much higher priority is to look for the other two elements in the source-medium-detector chain.

Resources

Download the support sheet / student worksheet for this activity.

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Listening to music with a new ear

Sound Wave
Light, Sound and Waves

Listening to music with a new ear

Classroom Activity for 11-14

What the Activity is for

Discussing a variety of sounds.

When teaching about sound it is fairly common practice to listen to musical instruments, or music of some kind, perhaps from an electronic keyboard. Here we show you how to deal with this variety of sounds, without having to discuss the differently shaped wiggly lines that appear on oscilloscope screens. In fact we point to something altogether more fundamental – the combination of the different frequencies in varying proportions, which create the soundscapes that we enjoy.

What to Prepare

  • a variety of musical instruments
  • software, plus computer and microphone, that allows you to look at different frequencies as they are played

What Happens During this Activity

Set up the software and hardware so that they show the frequencies present in any note as it is played. You'll need to experiment with the software that you choose, and probably read the manual. A plot of frequency against time is the target (such displays are often called spectrograms or spectrographs).

If practised, a useful first step is to whistle into the set-up, with a steadily increasing pitch. You should aim to produce a steady increase in frequency, consisting of a narrow band of frequencies: nearly a pure note. Use a spectrograph style display, with frequency plotted upwards and time scrolling along to explain how loudness and pitch show up on the screen.

Treat this as a familiarisation exercise.

When a particularly interesting trace is on the screen, freeze it. Point out the dominant frequency, often shown by being brightest, and the mixture of other frequencies present. Say that these are an important aspect of the way we identify the sound as coming from a particular instrument. Compare a number of instruments.

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Scanning with sound

Sound Wave
Light, Sound and Waves

Scanning with sound

Classroom Activity for 11-14

What the Activity is for

Creating a map with sound.

Sounds travel at a known speed, so you can find distances from the trip times. One common use of this is to fire a sound out and listen out for its echo. Bats use this in echo-location; we use it for ultrasound scans. Similar methods are used in sonar scanning for locating the bottom of the ocean. In this activity we show how a regularly spaced series of echo locations can map a terrain.

What to Prepare

  • a sonic tape measure (These are available from many hardware stores. This sends out an audible pulse, then reports the distance to the object you are facing.)

Per group:

  • plasticine, about 150 g
  • a straw
  • a ruler
  • graph paper
  • a prepared piece of electrical ducting

What Happens During this Activity

Introduce ranging by sound using the sonic ruler. It will work well over the ranges commonly available in the classroom. With better classes you might like to try softer targets, like a staggered row of pupils, to find the limits of the device. Which reflection does it latch onto?

Then to some practical activity.

Explain that the class are about to model the plotting of a sea floor by sonar. The top of the ducting represents the sea surface, along which their survey ship will travel. The holes show where they will take samples. The straws will be used to make the depth readings, simulating the sound reflecting off the sea floor. Their job is to produce a map of the sea floor.

We suggest that one pair use the plasticine to make a landscape (seascape?) inside the ducting, then clip the drilled lid on to hide the landscape. Then they should swap their creation with another pair to see how close each pair can get to a good map by making measurements.

There are subtleties, which you may leave them to figure out or choose to rehearse beforehand. They will measure depths, but their map probably wants to show heights. Some simple calculations can fix this.

More fundamentally, there is a distinct limit to the sensitivity of their measuring devices, as they cannot measure how far the straws go under the sea all that easily. Plus there is the issue of a limited number of samples, so that the resolution of their map is distinctly limited in the horizontal plane as well.

Both of these two are well worth discussion as they can help with an appreciation of the limits of any measurement process.

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Building up sounds

Sound Wave
Light, Sound and Waves

Building up sounds

Classroom Activity for 11-14

What the Activity is for

Exploring a combination of frequencies.

Few sounds consist of a pure tone of just one frequency. Here we show how different frequencies can be heard at once, at the same time as showing a representation of the motion of the vibrator making these noises (but slowed down a little!)

What to Prepare

  • a computer in the classroom, driving speakers loud enough for the class to hear, together with a data projector and a large screen
  • a copy of the interactive (see below)

What Happens During this Activity

Start with the simple tones, then play the more complex sounds. Draw attention to what the on-screen loudspeaker is doing. So that pupils can see this, it is 1000 times slower than the loudspeakers actually making the noise.

Say that we can make up any sound we like by combining the right balance of appropriate frequencies: a bit of 200 Hz, a lot of 1000 Hz and a lot of 3500 Hz make an interesting note.

Combining different amplitudes of chosen frequencies is how synthesisers work. As we said before, you can get a long way in sound building on amplitude and frequency.

For the more adventurous, many sound processing packages allow you add frequencies to your heart's content.

Resources

Download the interactive for this activity.

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