A more powerful speaker

The signal coming into our speaker was too weak to make a strong sound. We picked up a 3W signal amplifier kit from Radio Shack (Velleman K8066). T got to practice soldering hookup wire to alligator clips to get started. We (mostly I) soldered the kit together with a 9V battery for a power source. We mounted it on a small cardboard box and added an on/off switch "to make it more official" as M said. It works! The audio is as strong or stronger that the speakers on my laptop. It does very well with higher pitch "violin" range. I played Vivaldi, Four Seasons, Winter on it and T accused me of tricking him and actually playing it off the computer speaker, it was so clear and strong. It does poorly with lower human voice range (I tried Kennedy's speech at Rice University and his May 25, 1961 speech before congress but they were unintelligible), which probably helps explain why it was such a bad microphone for our voices. One interesting thing, when I played recordings made from using it as a microphone, back onto it as a speaker it shook like crazy. This demonstrates inducing mechanical resonance from the natural way the setup tends to vibrate. One last tweak I would like to add is a switch for flipping between unamplified microphone mode and amplified speaker mode.

Speaker success

I mentioned earlier that we tried to make a speaker for a weekend project (and also as a part of the kids education). It didn't work at all and I figured we needed more power. We were using ceramic magnets, so I ordered some more powerful neodymium magnets to play with. We also used more wraps (250) with thinner (32 gauge) wire to get a more powerful electromagnet coil to push and pull the magnet. These were glued to two plastic plates and one plate is supported over the other by springs. When it is hooked up to a battery you can see the top plate being pushed or pulled by the magnetic field interactions. We stripped a 1/8" audio cable and hooked it to our speaker then plugged it into the computer and played a song. It worked! Sort of. The sound was very faint, but if you listened closely you could hear the audio coming from the top plate. If you touch the plate you can clearly feel the vibrations.


We also plugged it into the microphone port and tried recording. It makes a very bad microphone but it does work to an extent. You have to lean close and speak loudly. There is a lot of hissing and so on but you can recognize a voice in the background. Here is a picture of the raw recording using Audacity.


Below I've amplified the signal and labeled places where T said "testing one two three."