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String Telephone Lab Report

String Telephone

Jade Turbides, Kyukyoung Kim, Carl Exhume, Sanbir Rahman, Mubdi Shah

Engl 21007 Writing for Engineering

Prof. Maryam Alikhani

City College of New York

October 15, 2018




To mimic and test the first telephone, we crafted a simple attachment of cups through the use of strings to demonstrate how sounds travel through the air. With the string tight enough, the sound waves of the sound presented in the cup vibrate back and forth among the string. The vibrations within the cup follow the sound waves causing the string to move back and forth. The modern telephone follows the same concept using electric current rather than a string. In our experiment, we found that copper wire produced the loudest sound due to its high conductivity.


Our group wanted to illustrate the roots and concepts of the modern telephone. Alexander G. Bell invented the first telephone by using coil and magnet to deliver the sound from one side to another through the wires (Figure 1). Our mission is to determine the most promising and effective means of communication through the use of cups and strings. We are interested in the effects that different media will have on the strength of the sound you hear coming from the cups. Our experiment will test the effectiveness of 3 different strings that include thread, yarn, and copper wire. We will be using the decibel (dB), which measures the intensity of a sound, to quantitatively compare the media.

The way the experiment works is that sound requires a source to vibrate at an audible frequency. These vibrations then travel through any solid, liquid or gaseous medium as longitudinal waves. Although sound waves can travel through air, solid media transmit sound more effectively due to their greater density. Speaking into the cup transmits the sound of the speaker’s voice into the bottom of the cup. The bottom of the cup then acts as a diaphragm and vibrates with the sound of the speaker’s voice (HowStuffWorks, 2000, Par. 4). As this happens, it transmits the vibrations into the string, which must be held taut. The sound travels along the taut string and vibrates the bottom of the receiving cup. The receiving cup then transmits the sound into the air around the listener’s ear, allowing them to hear the speaker’s voice.


Figure 1: Diagram of Alexander G. Bell’s first telephone (Telephone Invention, n.d.)







Materials and Methods


  • Plastic cups
  • Different wires and strings
    • Yarn (5 meters)
    • Copper wire (5 meters)
    • Needle and thread (5 meters)
  • Scissor
  • Tape
  • Ruler
  • Sound Meter
  • Sound source (Alert bell on phone)



  1. Using a needle, poke a small hole into the bottoms of two paper cups.
  2. Cut the wire and record the measured length. If you only have access to one wire each, start the lab with maximum length, and then cut the length of the wire down for different trials
  3. Insert wire through both holes and tape them down from the inside of the cups so that they will not disconnect during the experiment.
  4. Set up a sound meter in one cup and a sound source in the other. Record max and average dB produced.
  5. Repeat steps for each string at different lengths.







The max and average dB produced were recorded with respect to each length.


Table 1: “Data table of Maximum | Average decibel delivered for each wire.”


Material dB Recorded (5 ft) dB Recorded (4 ft) dB Recorded (3 ft)
Copper wire 60 | 52 62 | 53 67 | 57
Yarn 63 | 53 61 | 52 61 | 52
Thread 63 | 53 61 | 53 60 | 52




Table 1 shows that copper wire produces the greatest decibel, and this is scientifically logical because sound travels through copper at its second highest rate, 4600 meters per second after aluminum (6320m/s). Because copper is the second-least dense solid, it is more elastic and has more space for easier vibration, resulting in efficient sound travel (Allan, 2018, Par. 4). Although the speed of sound does not have a direct relationship with the intensity of sound, faster speed could reduce the sound waves being muffled during the travel. As a result, it is logical for copper wire to deliver the greatest decibels.

Because copper wires are very efficient in sound delivery, they are used various places. For example, along with aluminum wires, copper wires are the most common electric wires. Although they are not the best conductors, they are most commonly used due to their abundance and low cost (Whelan, 1).

There are few possibilities that could have caused insignificant change in decibels for yarn and thread after change in length. For example, the string wasn’t tight enough, so the sound wasn’t fully traveled. Also, the sound meter possibly couldn’t detect the difference between each trial’s decibels.



Through the experiment, we learned that the copper wire transmitted the loudest sound between the cups. Notably, there were a few discontinuities in the data such as the 5 ft trial where both yarn and thread outperformed the copper wire. This could be attributed to the ambient noise interfering with the results. Perhaps a thinner copper wire would transmit an even louder and more accurate sound. In addition, the intensity of the sound was measured using a sound meter through a cell phone’s microphone. This could have also introduced noise if the cellphone shifted inside the cup. Modern telephones do not have this issue as the electric current runs almost instantaneously through telephone lines. Thus, the telephone has come a long way to become the seamless mode of communication that we know today.





Allan, S. (2018, April 29). Which Materials Carry Sound Waves Best? Retrieved October 6, 2018, from https://sciencing.com/materials-carry-sound-waves-8342053.html

HowStuffWorks.com (2000, June 27). Can two cans and a string really be used to talk over a distance? Retrieved October 9, 2018, from https://science.howstuffworks.com/question410.html

Telephone Invention Stock Photos and Images. (n.d.). Retrieved October 14, 2018, from https://www.alamy.com/stock-photo/telephone-invention.html

Whelan, M. and Kornrumpf, W. (n.d.). Wires. Edison Tech Center. Retrieved October 6, 2018 from http://edisontechcenter.org/wires.html