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I purchase a new Yamaha RX-A740 7.2 receiver and want to add my first subwoofer, but need some clarification.

I noticed some subs have LFE and some don't. Though my receiver has 2 sub outs, nowhere in it's manual does it mention LFE. Should I look for a sub w/ LFE input or can I have a sub w/o it. (As an example, the Polk PSW10 does not nave LFE)
 

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The LFE part is more a designation than a true connection type.

For most subwoofer manufacturers their LFE input will bypass certain amplifier controls, like the crossover for example, whereas the Line In connections will still utilize them. The former is good for someone who wants their receiver to control those adjustments while the latter is better for folks who might want to do some fine tuning.

Both use the RCA style of connector though, so for all intents and purposes you can consider them interchangeable. There are slight variations between the two, but none significant enough to be worrisome. Your Polk will work just fine.
 

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Some of them just have an LFE mode as well but no separate input, like the Klipsch R-115SW, it is basically just turning the crossover all the way up, doesn't mean anything special other than it is just amplifying whatever it is being fed. If your receiver has a sub out then it should have an internal crossover, that's all you need.
 

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The LFE (low-frequency effects) channel is the .1 in a multi-channel (5.1, 7.1, etc.) audio stream. It contains LFE audio in the range of 0-120Hz.

All content in the LFE channel plus all bass content BELOW the crossover point (e.g., 80Hz) set for each of the speaker channels is output through an AVR's subwoofer output(s).

On the subwoofer itself, an "LFE" input tends to mean that using that input will bypass the sub's built-in "crossover" (actually a low-pass filter (LPF)).

If the sub does not have an "LFE" input, you can connect to either the left line-level input, the right one or both (the owner's manual will tell you which one(s) to use) and simply max out the sub's LPF to effectively bypass it.

(Sometimes, a sub will have an actual "bypass" switch that you can use to disable the LPF.)
 
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