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Re: [Phys-l] amplifier



You can reverse the phase digitally by using a computer program that does this. There are any number of audio processing programs which do this and can display the wave form. My favorite is Audio Cleaning Lab which just changed versions. The old version may be available cheaply or for free after a rebate. There are also a number of free processing programs on the web. You can also change the phase to an arbitrary value with many of these programs. ACL has a method of splitting the channels, and you can then slide one channel relative to the other to get any phase you want.

Is a virtual demo or lab effective?. The recent paper by McDermott in AJP demonstrates that they are equally effective, at least in the context of their Tutorials.

John M. Clement
Houston, TX


I'm teaching about sound and want to reverse speaker wires (red/black) to
show constructive/destructive interference of sound waves (music) with two
speakers/microphones and an oscilloscope. In the past I used cassette
tapes, an old boom box (volume turned up), and old speakers. I would
reverse the (red/black) wire connection (via alligator clips) for one
speaker while the music played. A bit cumbersome, but it worked.

I now have some songs on the computer (iTunes) and wish to repeat the
demo. However, the old stereo speakers (connected via the earphone jack on
the computer) are not loud enough. The new computer speakers are very
loud, because of the amplifier built in, but I don't want to strip the
wires on them.

So I need an "inexpensive" amplifier to boost the loudness from the
computer (1/8 "earphone jack) to my old speakers. Does anyone know where I
could purchase such an item? I assume Radio Shack might have some stuff.

Any better ways to do this demo?

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