how many ways to hook up a subwoofer

If it's a powered sub there won't be any issues connecting it to the speaker output of the amp.  Connect the sub between the amp and the main speakers. Your amp won't have any additional stress because the sub's amplifier will be powering the sub. 

Contrary to popular belief, some engineers actually recommend using the speaker level input of the subs instead of XLR or RCA because then the audio going into the subs will match the voicing (sound signature) of your power amplifier and will be the same as the voicing going to your main speakers, instead of the voicing of your preamp going to a sub and the voicing of your power amp going to the main speakers.  RCA connections is not recommended due to their tendency to pick up noise caused by ingress and XLR is recommended for long runs to avoid noise issues, but regardless, speaker level inputs are the preferred method of many engineers, for the aforementioned reason. 

I sure don't want to argue with @ellajeanelle, as obviously is a nice person, but I am involved with pro and consumer both and I cannot figure out what you are talking about with "voicing" of speaker outs vs line level (-10 RCA) or pro level (+4 balanced).  ALL sub set ups in professional applications are +4 XLR balanced, this is the single safest way to do it, straight from the source preamp, using a "Y" cord to split the preamp output between 2 destinations: #1 to amp (then to main speakers)  and #2 to the sub. 

Maybe by your phrase "carrying voicing" you mean some of these highly colored preamps, like an old tube unit, where the line level out is already changed based on the tube circuitry inside the preamp?  That would be a case where the line level output DOES carry the color of the preamp as the only circuitry inside the preamp is tube.   But in the case of most modern or solid state units, the line level output labeled "tape out" or "preamp level out" or "subwoofer out" would be relatively color free.  

If you use the speaker level sub input, aren't you adding the preamp output color to the amp color to the speaker cable color and finally to the sub?   

Brad     

lonemountain:  You are talking about professional applications and not what's being discussed.  See 2:20 on link: The best way to connect a subwoofer (youtube.com)

 BTW: I have several systems, both HIFI and professional and I know what you mean.  They are all connected differently and speaking for myself, the difference is an audible improvement if connected as described in the video!  Try it!  This video will clarify my post.   Thanks for your input.

Paul McGowan on "High Level" sub connection

Well, my subs (JL Audio) do not have a speaker (high level) connections, only RCA or XLR inputs, and I am going direct from my Lumin X1 to my mono blocks (no preamp). I did not want to use a Y adapter.

So, I purchased a Jenson ISO-Max unit that converts speaker outs (high impedance) to XLR (low impedance). Seems to work very well.

ozzy

@ellajeanelle    +1.

A requirement is having a subwoofer that has a 'high level input'. Connects from the output of the amp. This way it will respond to the character of the amp. If the amp is punchy you'll get that punch. If you run it from the preamp you will bypass the amp and NOT get that punch.

This was a VERY noticeable improvement in bass quality! (thanks Paul McGowen)

You can run a wire from the back of the Amp to the 'High level input' OR (my preferred method) go from the speaker with a short wire to the High level input.

Don't worry, the high level input just needs a tiny bit of signal and puts NO strain on the amp. The sub amp does all the heavy lifting.

@ozzy ,

would you mind mentioning the model number of the Jensen ISOMAX? I have a vintage system and that might be a good option for me, thinking of adding a sub to it.

thanks

Sure, it is the Jensen ISO-MAX SP-2SX 2 channel unit. I however am using 2 of them since my subs are very far apart.

ozzy

@chiefsteward1 you can run wire from your amp to the speakers and then from the speakers to the sub.The sub first then on to the speakers will work too.I use a y connector from the pre so I can make use of the built-in equalizer in the sub.There are a few other ways to do it also.

Thanks Ozzy