Amplified Speaker with Pickup Coil

#5K30.25

Description An amplifier driven speaker coupled to a magnetic pickup coil can produce a feedback squeal. The pickup coil also can detect the field around the speaker and on the transformer. Replace the coil with a microphone you can get a high frequency feedback squeal, and the squeal will be blocked when you insert a sheet of the foil between the speaker and the microphone.
Location 27E