# Exploring Can-and-String Phones: Frequency and Propagation Equations

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• kiki_danc
In summary, using cans and strings to hear someone's voice at the end results in a distorted and tinny sound due to the selective enhancement and suppression of frequencies. It is also affected by the tension and preferred modes of the string. There are commercially available can phones and they can also be referred to as tin can telephones. DIY examples can be found by searching "tin can telephone" on Google.

#### kiki_danc

I haven't tried using cans and strings to hear someone's voice at the end.. does it sound like a person voice or more tin like?

Any equations anywhere to compute for the frequency and propagation of the wave?

You will not be surprised to hear that it sounds awful. The frequencies of vibration from the air couple into vibration of the bottom of the tin can. The tin can bottom has modes and frequencies it vibrates well with little damping. These frequencies couple strongly into the tin can. The tin can does not vibrate well at other frequencies and these frequencies do not readily couple into the tin can. These modes can be described by the elastic constants of the can and the boundary conditions which for the bottom of the can are that the circular edge cannot vibrate (much). Look up drum modes. For a tin can some higher frequencies tend to vibrate more readily. If you would like to know which frequencies, thump the bottom of a can. That high metallic ring is what your voice will sound like and is the very definition of tinny.

The bottom of the can acting like a diaphragm picks up the sound from the air. The vibrating diaphragm then couples to the string or wire. The wire should be under tension. The string also has preferred modes determined by the length and tension. Look up modes on a string. These too selectively enhance some frequencies and suppress others so the voice is further distorted. The string also has dispersion. Different frequencies travel at different rates. The laser blaster sound from Star Wars was made by recording the sound of hitting a telephone pole guide wire with a screw driver. The high frequencies travel faster so you hear the high frequency echo before the low frequency. That’s what makes the distinctive downward chirp. Well the same thing happens on the tin can phone. High frequency travels faster, and that further distorts the voice smearing the consonants.

anorlunda, DrClaude and kiki_danc
Cutter Ketch said:
You will not be surprised to hear that it sounds awful. The frequencies of vibration from the air couple into vibration of the bottom of the tin can. The tin can bottom has modes and frequencies it vibrates well with little damping. These frequencies couple strongly into the tin can. The tin can does not vibrate well at other frequencies and these frequencies do not readily couple into the tin can. These modes can be described by the elastic constants of the can and the boundary conditions which for the bottom of the can are that the circular edge cannot vibrate (much). Look up drum modes. For a tin can some higher frequencies tend to vibrate more readily. If you would like to know which frequencies, thump the bottom of a can. That high metallic ring is what your voice will sound like and is the very definition of tinny.

The bottom of the can acting like a diaphragm picks up the sound from the air. The vibrating diaphragm then couples to the string or wire. The wire should be under tension. The string also has preferred modes determined by the length and tension. Look up modes on a string. These too selectively enhance some frequencies and suppress others so the voice is further distorted. The string also has dispersion. Different frequencies travel at different rates. The laser blaster sound from Star Wars was made by recording the sound of hitting a telephone pole guide wire with a screw driver. The high frequencies travel faster so you hear the high frequency echo before the low frequency. That’s what makes the distinctive downward chirp. Well the same thing happens on the tin can phone. High frequency travels faster, and that further distorts the voice smearing the consonants.
Is there commercially available can phone I can try (best model).. what would be other words for "can phone" that I can google at ebay?

kiki_danc said:
Is there commercially available can phone I can try (best model).

More pedantically, "steel cans plated with zinc (or whatever) to resist corrosion".

Try a Google search for "tin can telephone" for many DIY examples. I've never made one myself, but they were a common "meme" (in modern language) when I was a kid (in the US) more than 50 years ago.

davenn
kiki_danc said:
Is there commercially available can phone I can try (best model).. what would be other words for "can phone" that I can google at ebay?

This makes me laugh so hard!

davenn and sophiecentaur
I have used plastic cups, single use, too. They are very light weight and the base acts as a good diaphragm to pickup the air vibrations. (Well matched.)

jrmichler
My recollection of my can phone experiments is hazy because it was a long time ago. I do remember that string was almost useless, while a piece of thin copper wire worked much better.

Forget the equations until you have built and tested one. This is a case where an experiment is worth a thousand hypotheses, opinions, and equations.

Merlin3189, CWatters and sophiecentaur
jrmichler said:
I do remember that string was almost useless,
It's all a matter of matching the transducer to the transmission medium. (As always )

Cutter Ketch said:
You will not be surprised to hear that it sounds awful. The frequencies of vibration from the air couple into vibration of the bottom of the tin can. The tin can bottom has modes and frequencies it vibrates well with little damping. These frequencies couple strongly into the tin can. The tin can does not vibrate well at other frequencies and these frequencies do not readily couple into the tin can. These modes can be described by the elastic constants of the can and the boundary conditions which for the bottom of the can are that the circular edge cannot vibrate (much). Look up drum modes. For a tin can some higher frequencies tend to vibrate more readily. If you would like to know which frequencies, thump the bottom of a can. That high metallic ring is what your voice will sound like and is the very definition of tinny.

The bottom of the can acting like a diaphragm picks up the sound from the air. The vibrating diaphragm then couples to the string or wire. The wire should be under tension. The string also has preferred modes determined by the length and tension. Look up modes on a string. These too selectively enhance some frequencies and suppress others so the voice is further distorted. The string also has dispersion. Different frequencies travel at different rates. The laser blaster sound from Star Wars was made by recording the sound of hitting a telephone pole guide wire with a screw driver. The high frequencies travel faster so you hear the high frequency echo before the low frequency. That’s what makes the distinctive downward chirp. Well the same thing happens on the tin can phone. High frequency travels faster, and that further distorts the voice smearing the consonants.
If one uses a special alloy can (what is it?).. can it reproduce all frequencies and in combination with special string.. can it produce more natural voice?

Does one have any recording of any tin can phone sound so we can hear what it sounds like?

kiki_danc said:
If one uses a special alloy can (what is it?).. can it reproduce all frequencies and in combination with special string.. can it produce more natural voice?

Does one have any recording of any tin can phone sound so we can hear what it sounds like?
Good grief MAKE ONE and play with it …. it's not rocket science !
1) get 2 empty food tins
2) a 15 metre piece of string
3) punch/drill a hole in the centre of the end of each tin
4) thread one end of string through that small hole in the tin and tie a knot on the string INSIDE the can
5) do the same with the other tin
6) give one tin to a friend
7) the two of you move apart till string is tight and start talking/listeningas jtbell said

jtbell said:

I made one when I was 6 yrs old and has fun with it with my friends

Dave

Merlin3189, phinds and jrmichler
tin can is avoided in my place so I have to order one at amazon.. and since i'll order it.. may as well get an alloy... is there no computer simulation or calculations of it so I can study it while awaiting the order

kiki_danc said:
tin can is avoided in my place so I have to order one at amazon.. and since i'll order it.. may as well get an alloy... is there no computer simulation or calculations of it so I can study it while awaiting the order

The thing about the tin can is the shape. The bottom acts as a diaphragm that can be vibrated by the sound waves. Lots of other things with similar shape will work fine and maybe even better. Someone above mentioned plastic cups. The important thing is that it vibrates well, so give some can/cup like objects a thump and find something that sounds pretty live. Also string isn't the only choice. As Sophie suggested you want something that rings about the same as your can/cup. Try some different strings/wires and different tensions and see what works.

I read in wikipedia that 3 miles were the range of some tin can phones.. that's very long.. how did they do it?
https://en.wikipedia.org/wiki/Tin_can_telephone

"Their maximum range was very limited, but hundreds of technical innovations (resulting in about 300 patents) increased their range to approximately a half mile (800 m) or more under ideal conditions.[5] An example of one such company was Lemuel Mellett’s 'Pulsion Telephone Supply Company' of Massachusetts, which designed its version in 1888 and deployed it on railroad right-of-ways, purportedly with a range of 3 miles (4.8 km)."

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So I assume the 3 mile tin can acoustic phones described at wikipedia uses some sort of electricity to amplify the vibration of the tin can? Meaning the 3 mile wires have longitudinal movements to transmit the sound? Is this correct?

kiki_danc said:
tin can is avoided in my place so I have to order one at amazon.
Why not order some canned food on Amazon? That way, you can at least enjoy the food, even if the experiment does not go well.

davenn
There are lots of things you could use instead of a tin can. Anything that's roughly cylindrical with one end sealed, or hemispherical, or conical, should do, as long as it's the right size to hold to your mouth and to your ear, and made from a material you can punch a hole through. Examples:
• paper cup
• disposable plastic cup
• yoghurt pot, or other similar-shaped thin-plastic pot
• plastic bottle cut in two
• small cardboard box, with one end open
• inner cardboard tube from a toilet roll, with card or paper stuck across one end

Merlin3189 and davenn
i'm no longer inquiring about the simple tin can telephone but one commercial used in the 1900s that uses springs... the description I found says:

"However, later in the 19th century, “mechanical phone” systems — essentially elaborate versions of “two cans and a string” were actually used in areas not served by Bell’s phone system (and which evaded any of Bell’s patents). Some were complete exchanges with operator switchboards, such as Lemuel Mellett’s “Pulsion Telephone” invented in 1888 for use on American railways.

A newspaper article from 1889 reads as follows: “The Pulsion Telephone was a mechanical telephone which really seems as if it might rival the ordinary telephone, at any rate for moderate distances, has been recently exhibited on a 3 miles line, between Finchley-road and Hendon, on the Midland Railway [Editor’s Note: near London], under the name of the ‘Pulsion Telephone.’ It is the invention of Mr. Lemuel Mellett, of Boston, U.S. [Editor’s Note: Actually he was from Newton and then Somerville, Massachusetts.] The principle seems to be to have on the resounding-plate a number of small coiled springs held at one end only; these respond to various harmonic vibrations, and the vibration of the wire is taken up and reinforced, giving great distinctness of utterance. It seems not to matter much whether the wire is twisted or passes through loose earth. One peculiarity is that it can be tapped at any point by resting a hat upon the wire, a useful quality in case of accident, though evidently unfitting it for private messages.”

I can't find illustration of it. Anyone got any picture of "the resounding-plate a number of small coiled springs held at one end only"... this is just for historical curiosity.

It may well sound awful, but 'telephones' made with string and plastic (sorry!) cups still sound good enough to astound middle/high school students.

And you can kind of cross connect them - if you have two pairs of students, tying the two strings together in the middle means that when one speaks, the other three can all hear.

sophiecentaur
My experience is that I can shout further than getting the cans to convey a message...

coolul007 said:
My experience is that I can shout further than getting the cans to convey a message...
Yeah, but then mum can hear it too...

Tom.G
coolul007 said:
My experience is that I can shout further than getting the cans to convey a message...
The signal to interference ratio can be a lot better, though.

I suspect that a thin (.2 or .3 mm) carbon fibre rod would make a good medium; light weight, high modulus, good tensile strength. Fairly pricey for the average kid's budget.

sophiecentaur

## 1. How do can-and-string phones work?

Can-and-string phones utilize the principles of sound waves and vibrations to transmit sound from one can to another. When one person speaks into the can, the bottom of the can vibrates, which in turn creates sound waves that travel through the string to the other can. The vibrations in the second can's bottom then produce sound waves that can be heard by the person on the other end.

## 2. What factors affect the quality of sound transmitted through can-and-string phones?

The quality of sound transmitted through can-and-string phones can be affected by the tension of the string, the thickness and material of the string, the size and shape of the cans, and the distance between the cans. Other environmental factors such as background noise and interference can also impact the sound quality.

## 3. How do frequency and wavelength relate to can-and-string phones?

The frequency of a sound wave refers to the number of cycles or vibrations per second, while the wavelength is the distance between two consecutive peaks or troughs of a wave. In can-and-string phones, the frequency and wavelength of the sound waves transmitted through the string are directly related to the tension and length of the string. As the tension or length of the string changes, so does the frequency and wavelength of the sound waves.

## 4. Can can-and-string phones work over longer distances?

Can-and-string phones can work over longer distances, but the sound quality may decrease as the distance increases. This is because the longer the distance, the more energy the sound waves lose due to friction and other factors. Additionally, the string may become less taut, reducing the efficiency of sound transmission.

## 5. Are there any real-world applications for can-and-string phones?

While can-and-string phones may seem like a simple and outdated form of communication, they have been used in various real-world applications. For example, they have been used by hikers and campers to communicate over short distances, and by rescue teams during natural disasters when other forms of communication are not available. They can also be used in educational settings to teach about sound waves and frequency.