Elenco Upgrade Kit SC500 to SC750 - Manual (Page 116)

mode) have nearly all of their energy at a specific frequency like for
the hum.
“Square” or “rectangular” looking waveforms (like in
Project PC1) and most music have a series of mathematically-
related peaks, while “random” waveforms (like from blowing into the
microphone or several people talking at the same time) have a
frequency “blob” instead of distinct peaks.
Project #PC15
Speaker Microphone
OBJECTIVE: To see what your voice looks like in electrical
form.
A speaker uses electrical energy to create mechanical vibrations.
These vibrations create variations in air pressure, called sound
waves, which travel across the room. You “hear” sound when your
ears feel these air pressure variations. But if air pressure variations
reach the speaker from another source, they will cause it to vibrate
too. This, in turn, causes the speaker to create a small electrical
signal just like a microphone does (though not very efficiently, since
speakers were not designed to be microphones).
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Connect the PC-interface cable directly onto the speaker as shown;
no other parts are needed here. If continuing from the previous
experiment then close the Winscope program and run it again, to
reset the settings. Click on the On-Line button to activate.
Hold the speaker next to your mouth and talk into it to see what
your voice looks like after the speaker converts it to electrical
energy. Adjust the Y1 gain control to get the best view of it.
Notice that you need to set the gain control higher here than in the
preceding project using the microphone, since speakers were not
designed to be used in the same way.
You may switch to FFT mode and view the frequency spectrum in
the same manner as for the microphone project PC14.
On-Line button Y1 gain control