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Electromagnet Speaker
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Objective: To build a speaker with electromagnet field and voice coils Permitted Materials |
| 1. Magnetic coils wound from copper wire (any type of insulation) |
| 2. Cones and frames may be made from paper, cardboard, wood, plastic, tape or glue (any type) |
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* No metals other than the copper wire coils and iron core(s) may be used in any part of the construction. |
| * Permanent magnets may not be used. |
| * Parts taken from commercial speakers may not be used. |
| Other Constraints |
| 1. Coils must be hand wound - not commercial coils. Iron cores may be incorporated in the design. |
| 2. The speaker must fit completely in a box 30 cm. X 30 cm. X 30 cm. |
| 3. The speaker must be free standing facing upward. |
| 4. The field magnet and voice coil must be visible or easily accessible for inspection. |
| 5. Wires that connect to the voice coil and field coil must be at least 20 cm. long. |
| Testing Procedure |
| 1. The speaker will be placed facing upward on a table. A box (30 cm. X 30 cm. X 30cm.) with an attached microphone, will be placed over the speaker. |
| 2. A 400 Hz sine wave produced by a function generator will be amplified by a standard power operational amplifier (18 watts rms, 4-ohm output) and applied through a one-ohm resistor to the speaker. The signal produced by the microphone will be viewed on a digital oscilloscope/spectrum analyzer connected to a computer. |
| 3. The decibel level of the 400 Hz signal, as read from the spectrum analyzer, will determine the score. The highest level (loudest) wins. In the event of a tie, a run-off test using 1000 Hz will be held. |
| 4. Contestants wishing to do their own preliminary testing can closely duplicate the testing procedure by using one channel of a typical automobile tape or CD deck. A series resistor connected to the speaker voice coil (at least 1-ohm, 10 watts) is recommended to protect the deck’s internal amplifier. |
| 5. A battery eliminator ( 0-12 volts, 10 amps) will be made available to contestants, or they may furnish their own power source for the field coil. |