lpf?

What exactly is the LPF on an amplifier and what difference does it make if i have it on, off or at a different setting?

LPF = low pass filter - passes low frequency signal and reduces the amplitude of signals with frequencies higher than the cutoff frequency.

Plays the lows and not the highs. Is used to control what frequencies come out of subs and mids. You can usually set the frequency on most amps. Example: 80Hz low pass filter will filter out frquencies above 80Hz and 100Hz filter will filter out anything over 100Hz.. and so on..

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Another thing to take notice to is the cutoff slope. A higher slope will do a better job of filtering out those frequencies that are right above the cutoff. Just remember that a Low pass filter that is set to 80Hz will NOT completly cut off frequencies which are right above it. It will add resistance to the frequencies just above the cut off point which will quiet that output. but to make it simple for you, yes jettagli03 is correct.

audioman: dude, you really need to get educated on this stuff before you give advice. The information you are providing is ethier way off base, incomplete or speculation. The information jettagli03 is correct, the info you added is not.
"It will add resistance to the frequencies just above the cut off point which will quiet that output." this is just one of many examples.

As far as I know, the crossover will start to hold back the frequencies closet to the crossover point. So for instance if you have the low pass set to 80Hz, you will get everything below that. The crossover will "hold back" the frequencies right around 80, alittle bit above and alittle bit below, say between 70-90. Then the frequencies above that will be completly filtered out. The crossover will not in any situation completly cut off the frequencies at and above 80Hz. This is what I meant earlier but might have said it alittle confusing.

At no time does a crossover completely filter out a frequency.  Start reading HERE.

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Actually, cableguy, audioman's input was correct and reasonably accurate... I think what he added was reasonable, considering the oversimplified explanation (though still accurate, if not necessarily complete) of jetta. audioman's terminology might not have been completely correct, but it was still understandable.

TECHNICALLY, the frequency specifically mentioned (in your cases, 80Hz) is actually the point at which the output is 3dB BELOW the reference frequency. With a 6dB slope, the reference frequency is 60Hz, and at 100Hz, the output is 4.5dB below reference, and at 120Hz, the output is 6dB below, or 1/4 the output of reference. The mentioned frequency is called the "half-power" frequency, and is ALWAYS the half power frequency, regardless of the slope... The "half-power" point is the "pivot" on the imaginary line that is drawn between reference and completely shut off.

The slope simply determines how fast the output rolls off, or how much closer to "vertical" that imaginary line is.

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

I figured if the guy doesn't know a relatively simple term like "LPF" stands for then something too in depth would scare him and probably not be able to follow and understand, so I kept it simple.

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