output volume issues

[BOM]

First time poster here. Ive had my sp for a month now and have had no problems. Today i just got a powered monitor because i want to start mixing without headphones. I first plug the sp directly into the monitor rca to 1/4 and the volume is super low,annoyed i plug it in rca to a dj mixer which improves it but its still low. At first i think it must be the volume knob because ive read that can be an issue but it always works with headphones. Then thinking maybe its a bad cord i start checking cords. For some reason i unplug the stereo right on the sp line out and all the sudden boooom the speaker is bumping and the walls are shaking with loud noises. I plug the stereo right back in and the music goes back down to a whimper i then unplug stereo left and its bumping again. As long as either left or right is unplugged the signal is strong. Ive played my turntable through mixer and monitor so i know its the sp. It does this for both mono and stereo samples on the sampler. Its not a huge deal i guess but im so confused to whats going on. Any help would be appreciated.

[Euclid Ov Oåklånd]

I've been trying to read about polarity and phase for mixing/engineering understanding and it sounds like that might have something to do with it. You could be experiencing some sort of signal cancellation or reduction if there is a polarity or phase issue in your signal. I don't know how this might happen in your 404 or if that has something to do with it. If speakers in a hifi system are hooked up in reverse than the sound experience of the listener relative to the stereo speaker field/stage will change for the worse. Just a guess, I know someone on here will have knowledge on this subject far beyond my ramblings.

[CULP]

^ uh yeah..word up phase issues

i would just try running a 1/4 splitter from the headphone jack...jack

[BOM]

Hey guys thanks alot for the suggestions! It indeed was phase cancellation. I was kind of a dumb dumb and didnt think that a single monitor on its own is a mono device. So I broke down and bought another monitor which took care of my problems and everything sounds lovely now. Don't judge me too harshly because I'm pretty sure the people at guitar center did. Thanks again!

[Euclid Ov Oåklånd]

I didn't know any of that about phase or polarity in audio until a day or two ago, so I found it slightly serendipitous.
Here's a link to the actual article that put me on my little search into the subject.
http://www.izotope.com/artists/dave_moulton.asp?id=3

[tape smoke]

i stumble into the same problem converting stereo to mono then try to record it in stereo and its gone, nowhere to be heard from. so i made a stereo cable by chopping 2 1/4 inches and splicing them together.