14 - 14 TRANSDUCERS I INTRODUCTION Transduction is the...

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14: Transducers - 1 14 : T RANSDUCERS I. I NTRODUCTION Transduction is the changing of energy (or information) from one form to another. Microphones transduce acoustical energy into electrical energy (voltage); loudspeakers transduce voltage back into sound. Tape deck record and playback heads transduce electrical signals into magnetized regions on magnetic tape, and vice versa. CD players transduce the information recorded on a CD back into electrical energy. Thus, transducers are a crucial part of the study of acoustics. II. F ARADAY S L AW OF E LECTROMAGNETIC I NDUCTION The operation of most transducers is based on Faraday’s Law, which says that if you move a wire through a magnetic field (or vary the magnetic field strength through a coil of wire), a voltage will be produced in the wire. This physical fact is very useful in acoustics since sound is a mechanical vibration which can easily cause a small ribbon or membrane to move. A. A SINGLE WIRE MOVING IN A MAGNETIC FIELD 1. Hook one of the long blue banana-banana wires directly from one of the scope inputs to scope ground. Set the scope to a sensitive setting, say 10 mV/div, and then move the wire back and forth between the jaws of your large horseshoe magnet. Try to keep the magnet as far away from the oscilloscope as possible, since its large magnetic field badly distorts the scope display. Notice that to generate a larger signal you need to move the wire faster. Also try moving the wire in different directions, for example back-and-forth between the jaws as opposed to parallel to the jaws. 2. Build a ribbon microphone . a. You will need: A strong horseshoe magnet A plastic frame Two clean 1/8 in. brass rods A strip of 1/2 (or ¼) mil aluminized (or copperized) mylar Masking tape
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14: Transducers - 2 b. Clean the brass rods with Emery-paper for better contact. Tape the rods onto the plastic frame so that they stick out from the frame on one side, which will allow for easy attachment of alligator clips. Stretch the mylar so that it runs through the
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14 - 14 TRANSDUCERS I INTRODUCTION Transduction is the...

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