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This is a simple way to add a rear channel to any stereo system. In my pictures I show a third speaker wired up for testing, but the third speaker should be mounted in the rear. The rear speaker will play only what is different between the two channels. It is not very loud, but it is noticeable. The lower it's impedence the louder it will be. The speaker does not need to be as good of quality as your other speakers. Don't go spending a lot of money.

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This is not my original idea, nor is it new. Brian Eno discovered this and did a writeup about it in the early 1980s.

Step 1: Hooking It Up.

Attach one of the two wires from the rear channel to the positive connection for the left channel and the other one to the positive connection for the right. It does not matter which wire from the rear speaker goes to which channel.

How is it grounded then?
<p>From an audio engineering standpoint this has the same effect as <br>flipping the phase 180 degrees on either the left or right channel <br>(doesn't matter which) summing the left and right to mono (which also <br>cancels identical information) and then sending that too a third <br>speaker. So what is played out of the third speaker is truly different <br>information than what is played in the left and right speakers.</p><p>Grounding <br> isn't as simple as &quot;this is zero volts&quot; or &quot;this is negative&quot;. When <br>sound is sent to a speaker the + and - terminals actually flip flop in <br>sync with the sound signal. They are only really called + and - so that <br> (a) a rising waveform will push the cone out and a falling waveform <br>will pull the cone in and (b) to make sure you are connecting both <br>speakers up with the same polarity (which matters a lot in the low <br>frequency ranges of bass and kick drums or movie sound FX, hook one up wrong and the bass response will suffer and your music will sound like it's leaning towards one side).</p><p>As far <br>as what actually happens with the third speaker, when the + terminal of <br>the left speaker is more positive than the + terminal of the right <br>speaker the cone of the third speaker moves forward. When the right + <br>is more positive than left + the cone on the third speaker moves <br>backwards. Electricity in analog circuits is all about one voltage <br>relative to another and isn't usually as black and white like digital <br>circuits.</p><p>As an audio &quot;engineer&quot; myself, I'm very interested in seeing what this actually sounds like. Thanks for sharing this!</p>
Wow thank you for all that information, not really much for me to argue with there only listen and learn. Thank you.
All your really doing is creating a low sound quality mono speaker
Intereresting. I will have to try this out. Thanks for posting!

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Bio: Most of my instructables will be tutorials for Atmel microcontrollers, Arduino, or Raspberrypi. I try to show concepts that you can use in your own ... More »
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