Honest Experience on Effects of Subwoofer Please

I admit I did not read everyone else's answer, so apologize if I am repeating something.

First, what are your main speakers?  Some main speakers need a sub more than others.

A really good sub will be better at the lowest octave than pretty much any speaker.  This is not subtle, it is very, very obvious.

It's a matter of personal taste whether the sub is integrated well enough with your other speakers for your liking.

Benefits to the midbass are real IF main speakers are being CROSSED OVER at a higher frequency, that is to say if BASS frequencies are being diverted from the main speakers - they will be moving with smaller excursion so that should give a cleaner midrange, greater power handling.

If main speakers are still playing the whole range then benefits to mids would not be as obvious. Maybe could still occur somewhat if your need to turn the volume knob up changes with the introduction of a Sub.

"There is no replacement for displacement" (zero fidelity?)   If you need loud music in a large room, played with authority and accuracy, you need large woofers.   A more modern possibilty would be the use of small woofers combined with a ton of power and digital processing as some of the modern subwoofers just coming out recently.

There is a YouTube channel called Nemo Propaganda Reviews.  This dude knows more about subwoofers than anyone on earth!

My experience has been that subs are good for Mid-Fi and Home Theatre (not so much for HQ 2-channel).

Inevidently, once I got the a sub to integrate sound pressure level wise, with my speakers (current rotation is Quad 63, ML ESL and ET LFT VIII), in my dedicated listening room, it screws up the Detail, Timing, Sound Stage or Image. Over many years I tried Electronic Cross-Overs (the closest to good), DSP and passive circuits... the experiment is now (as of last month) permanently suspended.

To each his own...YMMV.... 

I chased bass nirvana only to realize that what I was really missing was great midrange performance. I ended up selling my Definitive Technology ST-L speakers (towers with powered subs) and a single Martin Logan 1100x Sub.

I listen to a wide range of music: Mostly jazz, female vocalists, some live rock and blues, some country, even some electronic dance music.

I now have Harbeth 30.2 XDs with 2 REL T/9x and I'm really happy. I use the speaker level connections from my tube amp but I also use the Low level sub-cable connection from my A/V processor for TV/Movies so I get the benefit of stereo bass for my analog system and low level effects for my 5.1 surround sound system.   

A1: In my stereo pair set up the effect is subtle and depends on the recording. They add power and depth, a richness that is something you can feel. I have them located very close to the main speakers, phase is 0, crossover 38Hz (estimated, 5 clicks) and gain is 10 clicks (less then 1/3). Of course your own room and speakers will dictate these settings. I probably adjusted these 100 times before I got to the point where I didn't feel the need to fiddle with them anymore because they "disappeared". 

A2: They fill in the bottom end. The kick, dynamics etc. come from the Harbeth's amazing mid-range. They cut off at 50Hz but that does not take into consideration the room which in my case is large. 

*Most of the music is above 40Hz

*You need a stereo pair, otherwise you are summing 2 discrete channels of low frequency signal into one speaker - seems really obvious when you think about it but I was doing it wrong for a few years before a good hi-fi shop owner showed me the way forward

*I may not have bought the RELs if I was willing to buy a more powerful amp (mine is 40w pc) and large, full range speakers but in comparison, what I ended up with was a bargain and I no longer feel like I'm missing something.     

@mijostyn --

+1

Many a sub(s) implementation appear strikingly meager, malnourished and of secondary consideration in its overall implementation. I'm guessing it's that mentality again; why have a couple or further multitude of (sub-)bass behemoths lying around in the listening space when you can have all but one the size of a small cathouse?

Because it isn't only about extension, but rather, as you so rightly point out, it's also and not least about the added sensation of power and effortlessness of presentation to instill that live feel of music, including the contribution from the main speakers here when properly high-passed.

And yet, what is it about "hi-fi" that very generally turns its back on the inherent power delivery and (truer) size of music and instead relegates it to something brute, unsophisticated and undesirable? You'd certainly think that the way this vital aspect of music reproduction is sorely dismissed either (and mostly) in silence and vehement reluctance, or even downright ridicule.

Anyone can feel free to implement subs the way they see fit, that really goes without saying, but augmenting the mains run full-range with smaller subs is really only the tip of the iceberg. Perhaps it points to the need for a more radical and re-defined approach in speaker implementation that should more readily see the acceptance of DSP and active configuration, in addition to letting size of speakers and subs have its say. The latter part has been stubbornly missed out for decades, so one wonders whether it will ever find any real traction with audiophiles at large.

It seems the way it works is that if you can't go the whole nine yards with regard to physics then make it appear that not doing so is actually to the benefit of sound reproduction; indeed, it becomes a rationale in itself. 

A lot of silliness get passed around with topics like this one, and all bloviating aside, subs aren't that difficult to set up, more than one helps tame standing waves but one sounds much better than none, and don't be afraid to try 'em. I have a few older RELs (no high pass nonsense needed) bought used and they're great.