Magnetic Speaker

Magnetic Speaker

Equations and Calculations

How does it work?

History

• Magnetic field at the center of a loop = B = (Uo x I)/(2R)

Uo = 4Pi x 10^-7 (T x M)/A

I = Current = Voltage/Resistance

R = Radius

• Resistance = (Resistivity x Length)/Area
• Resistance= ((1.7x10^-8)x(6))/((Pi) x (.25/(2x1000)^2) = 2.077926937
• I = (5)/(2.077926937) = 2.4062443
• B = ((4Pi x 10^-7) x (2.4062443))/(2 x .0254) = 5.9523145 x 10^-5

• Inside a speaker an electromagnet is placed in front of a permanent magnet
• The permanent magnet is fixed firmly into position whereas the electromagnet is mobile
• As pulses of electricity pass through the coil of the electromagnet, the direction of its magnetic field is rapidly changed
• This means that it is in turn attracted to and repelled from the permanent magnet, vibrating back and forth

• The first electrical speaker device was constructed and patented by Alexander Graham Bell in order to make the telephone
• Ernst Siemens and Nicola Tesla improved on Bell’s invention in 1877 and 1881 respectively
• Horace Short patented a loudspeaker design that used a compressed-air mechanism in 1898
• The use of a moving coil transducer was patented by Chester W. Rice and Edward W. Kellogg in 1924

How does it work?

What does it do?

• In order to translate an electrical signal into an audible sound, speakers contain an electromagnet: a metal coil which creates a magnetic field when an electric current flows through it
• This coil behaves much like a normal magnet but also has the ability to reverse the direction of the current in the coil and flip the poles of the magnet

• Speakers translate an electrical signal into audible sound (Transducer)
• Speakers enable us to listen to music on our phones, watch a movie in theaters, and speak with other people over the phone

The Discovery

• The history of magnetism dates back to earlier than 600 B.C., but it is only in the nineteenth century that scientists have begun to understand it and develop technology involving magnetism
• The Englishman William Gilbert (1540-1603) was the first to investigate the phenomenon of magnetism systematically by using scientific methods
• The present day understanding of is based on the theory of the motion and interactions of electrons in atoms (called quantum electrodynamics and was devleoped by Ernest Ising and Werner Heisenberg)

Step by Step

Applications

• Once you gather all the materials, coil half of the copper wire into a small loop and tape it to the bottom of the cup (on the outside)
• Using the other half of the same wire, create a larger loop, that the magnet will fit inside of, and tape it on top of the previous loop
• Take the gator clips and attach them to one end of the auxiliary cord (Make sure to sand down the ends of the wire)
• The other end of the auxiliary cord goes into your phone
• Place the magnet inside of the second coil (on the outside of the cup) and enjoy your music

• Magnetism is also involved in the use of compasses, burglar alarms, magnetometers (determining the strength of magnetic fields), MRIs, car horns, and electric bells

Calculations

Equipment/Parts List

• Plastic cup, copper wire, magnet, gator clips, tape, shoe box, auxiliary cord, scissors

• The unit for this answer is a Gauss but can also be a converted to a Tesla
• As a reference, the Earth's magnetic field at the surface is about .5 Gauss (.00005 Tesla)
• This calculation can help determine the strength or kind of magnet and electromagnet needed

Cost Estimate and Time

• The approximate cost is $25 with the copper wire and the magnet accounting for the majority of the cost
• The speaker takes approximately 2 hours to make (depending on your expertise and experience (I had none))