Honest Experience on Effects of Subwoofer Please

I, too, added an SVS Micro 3000. I've got a pair of KEF LS 50s. Though it took me some time to get it dialed in -- had it set too high in both volume and frequency rolloff initially -- once I got it right, it was, well, just right. I don't even think about it most days now. Which, I'm thinkin', is how it's supposed to work.

I run my sub at 50Hz with a steep crossover so it does not muddy the mid bass .  Subs can not adequately fill in the gap between the common 80Hz low pass and where a speaker with weak bass rolls off.  That's the main reasonI went backto floorstanders with plenty of bass.    They don't need a sub necessarily but the sub does not call attention to itself, it only pounds out the lowest notes.

I’ve found it depends on the room and the system. I’ve had set ups that no matter what I did I couldn’t get the sub dialed in and integrated correctly; the whole experience was frustrating. It either added no bass or you could totally hear the sub and it stood out. Sometimes these were in systems that needed a sub as the mains were LF restricted monitors or small towers.

On the other hand, I’ve had a couple of systems where adding a sub was magical and totally transformed the system. Like night and day different and better. My current system was taken to the next level by adding a sub and I wouldn’t go back in this particular room/system. YMMV.

@ryder, Subwoofers will always make an improvement more or less depending on what type of speakers you are using but there are rules that have to be followed to match the subwoofer correctly with the rest of the system. Trying to do it on the cheap can certainly be worse than doing it at all. My own experience with subwoofers goes back to 1978 when I bought my first pair. It was a love hate relationship. 

To make it brief, never start with just one subwoofer. Two is the minimum, the larger the better. You need a full two way digital crossover with delay capability. There are inexpensive ones out there now. The low pass filters that come with most subwoofers are a cheap and dirty way of messing up your system. You want to cross over as high as you can, 80 to 100 Hz anyway. I have heard systems operating at 125 Hz sound wonderful. Doing this lowers the distortion of everything else produce by your main system's woofers. Subs should always be placed right against a wall (1/4" off) or in a corner. They are more efficient this way and you cancel out a few early reflections. This is why delay capability is so important. You have to be able to match the subwoofer's phase and time with the main speakers or you just get mud in the crossover region. 

Done correctly subwoofers not only add low bass but a sense of power and effortlessness. The midrange becomes cleaner, more detailed and a system's headroom can improve up to 10 dB. That is twice as loud. There are very few systems that could not benefit from subwoofers. You can not get the feeling of a live performance without them.

I suppose REL subs implement the high pass crossover or filter.

No. REL's design philosophy is not use a high pass crossover with their subwoofers.