Many mono amplifiers have 4 Speaker output terminals (two positives and two negatives). Lets compare a stereo amplifier capable of driving a 2 ohm load on each channel to a mono amplifier capable of driving a 2 ohm load. Let's say that we have four 4 ohm speakers. If we want to run all 4 speakers on the stereo amplifier, we would simply connect 2 speakers to each channel. Now, when we look at the mono amplifier amp with 4 speaker terminals (the same number as the stereo amplifier), you might think that you can connect 2 speakers to each pair of speaker terminals. The problem is... the speaker terminals inside the amp are connected together in a parallel configuration (2 positives together 2 negatives together). So, if we connect 2 speakers to each pair of speaker terminals on the amplifier, we actually have a 1 ohm load. You can check to see if the terminals are in parallel with an ohm meter.
It took me a while to find this , it was posted by "speakerman" in the installation tips sticky, i knew i read it somewhere... Anyway this is what i was talking about. How can you check to see if the terminals of an amp are parallel with an ohm meter:
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