To build a speaker with electromagnet field and voice coils.
- Magnetic coils wound from copper wire (any type of insulation)
- Cones and frames may be made from paper, cardboard, wood, plastic, tape or glue (any type)
- 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.
- Coils must be hand wound - not commercial coils. Iron cores may be incorporated in the design.
- The speaker must fit completely in a box 30 cm. X 30 cm. X 30 cm.
- The speaker must be free standing facing upward.
- The field magnet and voice coil must be visible or easily accessible for inspection.
- Wires that connect to the voice coil and field coil must be at least 20 cm. long.
- 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.
- 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.
- 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.
- 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.
- A battery eliminator ( 0-12 volts, 10 amps) will be made available to contestants during the competition, or they may furnish their own power source for the field coil.
- None of the testing equipment will be available for practice runs prior to the actual competition.
Testing Equipment – Decibel Measurement
College of Saint Benedict
Saint John’s University
Chair, Physics Department
SJU PEngl 107