What it shows
A wide cone gathers sound waves from a large area and funnels them into the ear, so faint sounds become louder and clearer. Used the other way round, it sends your voice in one direction like a megaphone.
The science
Sound spreads out from its source in all directions, so only a tiny part of it normally reaches the small opening of your ear. A wide cone catches all the sound that falls on its big mouth and reflects it inwards along the narrowing walls, concentrating that energy at the small end where your ear is. Reversing it, your voice is stopped from spreading sideways and is sent forward in a narrower beam, so it travels further in that direction. Old hearing aids, a doctor’s stethoscope and a cheerleader’s megaphone all use this idea.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A sheet of chart paper or a flattened cardboard carton (free)
- A kitchen roll tube or a rolled card for the handle end
- Tape and scissors
- A ticking clock or a phone playing softly as the sound source
- A measuring tape
Safety
For this project: Never shout through the megaphone into someone’s ear, and keep the small end clean if it goes near the ear.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Roll the chart paper into a cone with a mouth about 25 cm across and a small end about 2 cm across, and tape it along the seam.
Tape the kitchen roll tube to the small end so you can hold it comfortably near your ear.
Set the clock or phone playing softly on a table and walk away until you can only just hear it; mark the spot.
Hold the small end of the cone to your ear, point the mouth at the source and walk further back until it just fades again; mark and measure the difference.
Turn the cone to point away from the source and notice the sound drops away, which shows the cone is directional.
Make a second, smaller cone and test whether it collects as much sound as the big one.
Speak through the cone from the small end to a friend across the room, then without it, and ask which was clearer.
Record all the distances in a table and explain the results with a drawing of sound waves being funnelled.
What you should see
With the ear trumpet, the soft ticking can be heard from noticeably further away, often half as far again, and only when the cone points at the source. As a megaphone, the voice carries further in the direction it points.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why does the cone make faint sounds louder?
It collects sound from a large area and funnels it into the small opening of the ear.
2Why must it point at the sound?
The cone only catches sound coming into its wide mouth; from the side the sound misses it.
3What happens when you speak through it the other way?
It stops the voice spreading sideways and sends it forward, like a megaphone.
4Name a real device that works like this.
A stethoscope, a megaphone or the ear trumpets used before electronic hearing aids.
Take it further
Make a stethoscope from a funnel and a length of rubber tube and listen to a friend’s heartbeat.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
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