Why the fascination with subwoofers?


I have noticed many posts with questions about adding subwoofers to an audio system. Why the fascination with subwoofers? I guess I understand why any audiophile would want to hear more tight bass in their audio system, but why add a subwoofer to an existing audio system when they don’t always perform well, are costly, and are difficult to integrate with the many varied speakers offered. Additionally, why wouldn’t any audiophile first choose a speaker with a well designed bass driver designed, engineered and BUILT INTO that same cabinet? If anyone’s speakers were not giving enough tight bass, why wouldn’t that person sell those speakers and buy a pair that does have tight bass?
2psyop
@2psyop - perception, cost, wow-factor etc...

Having said that - I do not have sub's, because I chose speakers that have pretty good bass performance, certainly good enought for most recorded "music"

Whereas - if you like to hear LFE's that are present in music, then subs are required
e.g.
  • if you like pipe organ music then sub's will convey those really low wall shaking frequncies
  • also some artists have recorded trucks and other sound effects that require them
  • electronic music can also go to very low frequncies

Some peoples speakers may require augmentation of the lower frequencies  e.g. bookshelf/monitor speakers

They can be more affordable than upgrading to a speaker that has comparable bass perofrmance .

There may be a perception in some peopled minds that without subs they are missing something.

And a big 12" or 15" sub certainly look impressive (throbbing away in the corners)

I do have a sub on my A/V system and I agree that it is complex to...
  • find the right match (size and performance) to your system
  • get the sound perfectly balanced

 It's a personal preference and not suited to everyone on every system - but they can add to a performance if the L/R speakers are lacking.

Regards - Steve
It really is personal preference as ww states.I find it easier to get deep and articulate bass by using subs that can be positioned and adjusted  to work with my room.
Many speakers that are "full range" are either

1) placed in a space that is too large for them to pressurize properly

and/or

2) inadequate setup of gear in front of them.

Subs help fill out the bottom octaves if listening to music that has "music" in the bottom octaves.

That’s been my personal experience.

As to subs being difficult to integrate, I must have just gotten lucky (you can look at my virtual system). My Kef R400b sub perfectly compliments my R11's, which i believe only go down to 32Hz. I run the mains full range and cross over the sub around 60Hz. It fattens up the bass guitar and gives the kick drum and lower tom toms a little girth.

I can't tell where the sub is located in the room if I close my eyes. I also don't feel like I need another sub either, as I've heard multiple subs is preferrable to one sub.

To each their own. I happen to enjoy the music with sub added. YMMV



 
I guess I understand why any audiophile would want to hear more tight bass in their audio system, but why add a subwoofer to an existing audio system when they don’t always perform well, are costly, and are difficult to integrate with the many varied speakers offered.

its not tight bass its low bass. Most floorstanders cant go flat to 18hz. Subs will help to achieve that. Human hearing is 20~20khz. 



Some peoples speakers may require augmentation of the lower frequencies e.g. bookshelf/monitor speakers

They can be more affordable than upgrading to a speaker that has comparable bass perofrmance .
My case precisely. I like very few speakers but fell in love the sound of EgglestonWorks speakers but could only afford the Fontaines, not their bigger brother the Andras. The Fontaines require LF augmentation, the Andras, with their 12" woofers, do not. So I did what I could - added a pair of 12" powered subs, moved them to optimal positions within the room for smoothest bass response ... and voila! Andras sound on the cheap (relatively).

And contrary to the OP’s opinion, they (ACI Titans) perform very well, were not costly (relatively), and were not difficult to integrate.
very very few speakers put out 20hz bass at realistic volume levels 10 feet away; even if they are rated at low bass levels, that is at inches away and at very low volume...subs add a lot, not just bass, but make a huge difference to mids and highs...they can be difficult to place and integrate, therefore much debate and discussion...my speakers are rated at -3db at 29hz, and a single REL S/5 SHO has made a great difference, though my room fortunately made for easy placement of a single sub...
One problem with full range systems is that standing waves often exist in the listening room. This can mean bass in most areas except the listening chair. The solution isn't room treatment, its placement of several subs in such a way as to break up the standing wave.

The Audiokinesis Swarm is thus one of the best sub systems made.

My speakers (Classic Audio Loudspeakers T-3) go down to 20Hz flat no worries. But I still have to employ subs to break up the standing wave else the bottom octave is not audible at the listening position although it certainly is everywhere else in the house. 
2psyop
why add a subwoofer to an existing audio system when they don’t always perform well, are costly, and are difficult to integrate with the many varied speakers offered.


Why indeed? I sure never would. That would be crazy. Instead I would add one that performs well, is affordable, and integrates well.
See what you did there? Built a straw man in the guise of a question. Don’t do that.

Additionally, why wouldn’t any audiophile first choose a speaker with a well designed bass driver designed, engineered and BUILT INTO that same cabinet?

Many do try to do just that. Look around however, it quickly becomes very obvious the hardest most expensive thing you can find is two quality speakers with true 20 Hz bass. They essentially do not exist. Turns out (read on) that for reasons of physics they cannot exist. Which is why they don’t.

If anyone’s speakers were not giving enough tight bass, why wouldn’t that person sell those speakers and buy a pair that does have tight bass?


Well now you’ve confused tight bass with extended bass. Tight responsive bass is not all that hard. Tight responsive deep bass, that is so hard it borders on impossible. In fact it turns out that thanks to the particular combination of physics and human hearing that rules the lowest frequencies there’s really only one good way of doing it.

Also your question ignores the fact there’s more to music than low bass, and a lot of people love the way their speakers sound, and just wish for that plus really nice solid low bass extension.

Add to that, the cost of adding a really good distributed bass array is far less than a new set of speakers, at least ones that will get you anywhere near as good bass response.

Finally, they say you don’t know what you’ve got till its gone. In this case though its more you don’t know what you’ve been missing till its there. So its the unknown. Nothing more fascinating than that.
+1 millercarbon

There’s a lot music happening below 40 hz. Very few systems can reproduce it properly. With most, it sounds like a muddy goulash. The complexity of reproducing a 96 piece orchestra is quite different than that of a singer/songwriter. Beethoven might be disappointed if the audience wasn’t hearing what he composed. Sting would be also if you couldn’t hear the opening of ’A Thousand Years.’

" . . . why wouldn’t any audiophile first choose a speaker with a well designed bass driver designed, engineered and BUILT INTO that same cabinet?"
As @atmasphere pointed out, the sound waves coming from the speakers significantly interact with the room. The key is to get all those sound waves to arrive & integrate coherently at the listening chair. Bass sound waves are particularly challenging. Separate powered subwoofers, offer the capability to deal with room nodes - via their physical location within the room - along with EQ & phase controls. With built-in passive woofers in floorstanders, there is minimal ability to correct for room anomalies. Several speaker designs have built-in powered woofers in their floorstanders to help compensate - such as Legacy and Vandersteen. Years ago, Verity Audio, built their Ovations with a bass cabinet that could be swiveled in a different direction to compensate for standing waves. Now, room correction built-into the preamp/processor is becoming popular.


" . . .and are difficult to integrate . . ."
Sometimes, yes. Sometimes, no. It takes considerable effort to get the over 40hz working well. Why not invest the time to the under 40hz working well along with it.


It’s no fascination, but rather a measured extension of your speakers limitations

Here’s an edited précis from one of a buzzilion prior posts on this subject

“.... A crossover is inserted into your signal path in order to remove the lowest frequencies (the deep bass) from your main speakers so that they no longer have to do all of the dirty work. The deep bass will instead be dealt with by the subwoofer.

The #1 benefit of adding a high quality subwoofer to your system is not how it further extends the bass response, but how it can dramatically improve the sound of your existing power amp and main speakers from the midrange on up. That, my friends, is by far the most compelling reason to add a sub to your high-end music system. Once your main speakers are freed from the burden of making deep bass, they will sound cleaner, faster and clearer, especially in the midrange and midbass.

They will also image way better because there will be far less air pressure and therefore resonance and vibration affecting their cabinet walls.

And since the power required to make the deep bass is provided by the subwoofer’s built-in amplifier, your main power amp will be free from that burden and begin to sound like a much more powerful amplifier.

The one big problem with all of this is that you need a good crossover to roll off the deep bass in your system and achieve all of these benefits...”

Dear @2psyop : Here are some reasons why I use two self powered subs wired in stereo fashion:

https://forum.audiogon.com/discussions/do-you-think-you-need-a-subwoofer/post?postid=310058#310058


You only needs two subs.

Regards and enjoy the MUSIC NOT DISTORTIONS,
R.
Because they work.
People that are into them are into them, and I have no issue with that, but I don't want to be bothered with all of the mess myself, and I feel my main speakers give me all of the bass that I need. 
Subs are simply just another very flexible and cost effective way to get extended bass when needed or desired , often in combo with smaller speakers with less bass extension, of which there are many very good quality affordable ones otherwise.

I use a fairly compact but extended 8" sub in one room which has tight quarters and with very high quality smaller speakers with limited bass extension that benefit.

I don’t use one, though I could, in others where the larger main speakers used do extended bass quite well alone.

I also don’t use one out on the deck where I run another pair of good quality smaller outdoor speakers with limited bass extension, mainly because I do not care about bass extension out there.

So like most things it all depends. Many ways to skin the cat, if needed.
@akg_ca 
The one big problem with all of this is that you need a good crossover to roll off the deep bass in your system and achieve all of these benefits...”
So, I gotta ask, where do I get that crossover?
Vandersteen makes their M7-HP, which looks like a high quality unit (pricy) and I would be interested but unfortunately the 100 Hz high pass is higher than the (40-50 Hz range) frequency that I would want.  Also, based on the images of their unit, this seems to be a bit more complicated than an in-line capacitor so maybe not achievable as a DIY project.

Back to the OPs question, I would look at one sub for an HT set-up and two or more for music.  By using mains with excellent sounding bass that is limited to a cut-off at about 40Hz, and then rolling in subs for their greater control at the lower frequencies below 40 Hz, I have eliminated low frequency room interactions and greatly increased bass drive. 
Generally people would be probably be better off using vibration isolation for the front end, in terms of getting more detail and slam in the bass as well as avoiding interference in the midrange. There are many ways to skin a cat.
1) Most speakers get to maybe 40Hz at reference levels. Even if they state say 30Hz +/-3dB, that’s at only 1 watt, many will dynamically compress.

2) Many songs go down to 30Hz or 35Hz. Some music with pipe organs go to around 16Hz. Movies have gone as deep as 10Hz.

3) Alleviating the bass from your speakers and amplifier(s) will ease their burden, thus usually allowing them to get louder, and thus be more dynamic.

4) Subwoofers have far more headroom, thus you can do a lot more DSP on a subwoofer at 60Hz than you can for a speaker at 60Hz.

5) The best place for baseball in your room is most likely not where the speakers are, having subwoofers allow you to find their best place in the room for where you sit. Of course, if localizability is an issue, keep them near the speakers.

6) People over-estimate how much bass they currently get. I was content with the bass from my cheap 8” sub, I thought it went decently deep and went decently loud, but I was so wrong, once I got a decent 12”, it was night and day, more of a difference than upgrading from $400 speakers to $40,000 speakers.
Thanks @mapman 
I am not necessarily looking for affordable but rather something that would be absolutely transparent since I would be high passing the entire signal above 40 or 50 Hz that is going to my main speakers.  That is one reason I have been curious about the Vandersteen model since I suspect it is about as transparent as these things get and plus it is simple, and another plus is that it is balanced, which is how the cabling is in my system.  I have thought about the Marchand units and they do make a balanced passive unit with poly caps and "high quality" inductors, at a reasonable price but I have not pulled the trigger since my roll-off/hand-off at around 40 Hz seems to be working and my amps are powerful enough that inserting the crossover might be creating issues to solve an issue that doesn't exist.  Maybe I should give one a try just to see. 
@mitch2 ,
I am glad you are considering the Vandy subs.
To me, they are the best way to add lower frequencies to a speaker- A simple 1st order crossover that eliminates frequency overlap and allows you amp to function at peak performance.
Once I sell my 2w and 2wq subs, I will be getting the new Sub 3 model.
Bob
I match a pair of Paradigm Servo 15's with my Apogee Duetta Sigs to pick up the 30 hz below the range of the Sigs. Sounds great on all music genres and did not cost a fortune. Got them used on Agon.
Sub(s) make listening a fuller richer experience. Even when not optimally placed they help. They don't take too much messing about to get them sounding/feeling right. 

For watching movies with explosions then a big and loud sub(s) add a lot. For music more nuanced is all that's needed. 

For young men in cars it's essential to have one that annoys other drivers and people in their houses. Not!
...and then, there are the few of us that do not have the financial means to afford such all-inclusive systems and add sub-woofers in an attempt to add depth & resonance (due to inferior equipment) for more listening enjoyment. We make due the best that we can.
I like to feel the bass and adding a sub (or pair in my case) which is designed solely to provide bass, I have found with experience that adding a sub or subs is the best solution. Not everybody can afford or accommodate bigger more costly stereo main speakers.

You can place a sub pretty much where you want, nice and tucked away in a corner behind your main speakers. I use two RELs, 1 Stentor and 1 REL Studio, and cannot imagine a main stereo speaker that would produce such low deep tight bottom end, unless I had the money to buy much bigger more costly main stereo speakers.

As for integration the REL subwoofers are unique in that you connect them from the amplifiers speaker terminals to the RELs high level input, so the subs receive the same signal as your mains, the RELs have various crossover and volume settings, to perfectly integrate with your room and main front loudspeakers.

The only loudspeakers I have owned that provided similar quality bass was the JBL Everest (65,000) and Nola Grand Reference (150,000) and both required adequate power amplifiers Edge NL Reference (170,000), my pair of RELs cost me 1500 and have built in 200 watt and 300 watt active mos-fet amplifiers, its a know brainer for me nowadays. I get excellent bass you can feel, they really have opened up, and added scale and depth to the soundstage. Adding a touch of warmth and body to the mid range, which I love and could not live without.
but why add a subwoofer to an existing audio system when they don’t always perform well, are costly, and are difficult to integrate with the many varied speakers offered.

This is a question I often have to ask before answering a poster's question about full range vs. sat/subwoofer systems, or adding a subwoofer to an existing system.


Fortunately, room correction matters and is getting better and more automated, so simple it's almost ready for cavemen.


On the other hand, honestly, half of all "audiophiles" have no ear at all and for them more is just better.


Additionally, why wouldn’t any audiophile first choose a speaker with a well designed bass driver designed, engineered and BUILT INTO that same cabinet? If anyone’s speakers were not giving enough tight bass, why wouldn’t that person sell those speakers and buy a pair that does have tight bass? 

A sub, well integrated, has a number of advantages. Can go deeper, can be optimally placed, and can be EQ corrected.


Going back to your first point, you are better off with a bass limited (45Hz or higher) speaker which is not going to wake the dragons, than a big speaker that can go low which you don't know what to do with.


Best,
E

I had been low-passing at 40 Hz using a pair of Velodyne HGS-10s with acoustic room correction by an SMS-1 to supplement a pair of KEF Ref 1s.  With some trepidation I recently introduced a fully balanced passive Marchand 80 Hz 24 dB/octave filter between the Ayre KX-5/20 and VX-5/20, reset the subs to 80 Hz 24 dB/octave, and reran acoustic room correction.  First consideration was that the filter do no harm to the Ayre sound, and it doesn't -- an active Bryston 10B had.  At first I doubted the filter had any perceivable effect, but with further listening to a wide variety of music I perceive more detail since the introduction of the filter.
If you have good speakers, you don’t want a sub-woofer. In my opinion, it “rapes”your music. 
I completely agressie with Millercarbon and Roxy54.
And , Kenjit: Human hearing is 20 hz-20 kHz for a your child. Till 18 kHz for a young adult. An older person: till 16 kHz.
subwoofers are not my cup of thee.
If you have good speakers, you don’t want a sub-woofer. In my opinion, it “rapes”your music.


A well integrated sub is a glorious thing. Absolutely amazing.


About 1% of all subwoofer systems I've heard were properly integrated. 

This is the problem. There's nothing inherently wrong with subs, it's how absolutely incredibly difficult it is to integrate them into the right room and with the main speakers unless :

1 - You have kick ass room correction/ calibration
2 - You are already a speaker maker.



Best,

E
Hello 2pyop,

I think a better question is why would anyone expect 2 full-range floor standing speakers, no matter their quality or price, to be able to provide both good bass response and good midrange/treble response at a designated listening seat when the low frequency sections of the speakers are not able to be independently positioned in the room. This makes as little sense to me as the use of subs apparently does to you.

It’s well known that bass soundwaves behave very differently in any given room than midrange/treble soundwaves will behave in the same room, mainly due to physics. The frequency of soundwaves are directly related to their length, the lower the frequency the longer the sound wave. This equates to a 20 Hz deep bass soundwave being 56 feet long and a 20,000 Hz treble soundwave being .056 inches long.

Humans are very adept at determining the originating location of midrange/treble frequencies but very poor at determining the originating location of bass frequencies at or below about 80 Hz. In other words, midrange/treble frequencies are very directional and deep bass frequencies are not.
All soundwaves, once launched, continue to move forward and bounce or reflect off any room boundaries (floor, ceiling, walls) they encounter along the way until they run out of energy. This regularly results in direct and reflected soundwaves meeting/colliding which causes frequencies to be perceived at these spots (called room modes) in the room to be exaggerated, attenuated or even cancelled.
Midrange/treble room modes are generally perceived as a sense of ’airiness’ and ’liveliness’ and the modes can be significantly reduced in any room via room treatment panels. Bass room modes are generally perceived as a sense that the bass is not smooth and natural and the modes can only be reduced, according to traditional thinking, via expensive and large bass trap room treatments.
There is another proven alternative method, however, that takes a very different approach called a distributed bass array (dba) that utilizes the principles of psycho acoustics to provide excellent perceived bass response throughout the entire room, not just at a single dedicated sweet spot. These complete dba systems can be purchased for $2,800 from Audio Kinesis as either the Swarm or Debra system. The main difference being the Swarm subs are a bit shorter and wider than the Debra subs.
Both systems include four 4 ohm subs with 10" aluminum long-throw drivers and a single class AB 1K watt amp that drives all 4 subs. The subs are strategically distributed within the room and their purpose is to create many bass modes (peaks, dips and nulls) in the room with the knowledge that our brains will process these numerous varying modes by averaging them out.
I’ve used the AK Debra dba system for about 4 years now. This concept works like a charm and provides bass that is very accurate, natural, detailed and smooth throughout my entire 23 x 16 x 8 foot room. It provides what I consider sota bass performance that is able to reproduce whatever bass the content calls for; rhythmic, taut and detailed bass for music as well as sudden, deep and powerful bass for ht and music. Here’s a review from the Absolute Sound on the A K Swarm system:
www.theabsolutesound.com/articles/audiokinesis-swarm-subwoofer-system/

Tim
I too was happy with my sound and thought it was great. I later added 2 subs and wow. It is not about deeper bass it is about realistic bass, you can feel the kick of the drum and it is how it sounds at a concert, tight and defined. The main reason for subs however has nothing to do with bass it’s all about soundstage. Adding subs makes whatever soundstage you currently have much better and deeper, it is much more 3D like. I was sceptical but boy was I wrong. I would say that if you don,t try subs you will never know what you are missing, go into an audio shop and get a demo it costs nothing. I thought I was happy with my system but trying subs meant I had to have them in my system and they are the best single upgrade I have ever made. My system is a £60k system with full range speakers but without powered bass they are not and can never be full range. You owe it to yourself as an music listener to give it a try, if it’s not to your taste then great 

I love extended bass woofers. I'm not so crazy about the sound of subwoofer drivers per say, but bass extension drivers are wonderful to have in a system. Not only do they give you great bottom end but also balance out the harmonic structures in the room making the highs smoother and the midrange fuller and more life like.

Michael Green

http://www.michaelgreenaudio.net/

It's affordable to add a sub to your system, versus buying full range.  You do not have to spend big bucks to get a sub now.  What full range speakers are you referring too?  It all depends on your mains, if your speakers are flat down to 20 hertz, you really don't need a sub, unless you listen to some rap or other bass heavy tracks.  If you want to get low, you need a sub.
My system sounded much better after removing the subwoofers.  A friend of mine asked what subwoofer should he be looking at to replace a dying one and I told him that his speakers had dual 8" woofers and his room was rather smallish so he absolutely didn't need a subwoofer.  He took it out, listened for a while, and realized he just saved a few thousand dollars.
Many people today like loud rock music.  Live, these songs are aided by towers of lousy speakers driven by even worse amplifiers that the move so much air the stadium shakes. 

People who have grown up with this thumping noise and gut-punching "music" want to reproduce that in their home and car systems; subs help IF they are efficient enough to work with their internal amp (powered) or your external amp--needs to be rather powerful unless you have Cerwin-Vega or other very efficient bass-heavy speakers.

Orchestral music that features actual music or sounds and harmonics (cannons, for example??) that enter the lower frequencies that humans can hear also require speakers that reproduce those frequencies accurately.

Systems that incorporate large bass cabs, like the old Mark Levinson HQD system, which used 24" Hartley speakers in huge cabs, actually CAN reproduce those frequencies given enough CLEAN amplification and the proper crossovers, etc.  Such systems not only give the listener the "live" experience, but also provide (as accurately as possible in a reproducing system) the live orchestral experience.

Finally, film buffs who have exotic home theater systems use them to reproduce the artificially-enhanced soundtrack of their fav films showing buildings blowing up--not really in the 20HZ range, but ENHANCED is the key item here--and other loud, gut-punching sounds that are really in the lower mid-range, but who's quibbling when your room is shaking and your stomach is pounding?  

Soon, we will have holographic films where the action will take place IN YOUR ROOM, or seem to, anyway.  Sound in those cases has to envelop the viewer/listener, and the love of the gut-punch or explosion at 120db is what people seem to want.  Well, until their ENT doctor gets ahold of their hearing tests, anyway...

Cheeers!


IT's probably true subwoofers get a bad rap with audiophiles because in many cases they are set up in a manner that adds too much bass which can also obscure the higher frequencies.  

But like anything else, its just a matter of doing it right, using the right sub set up the right way.    

The best setups do all frequencies in music one might hear well, generally accepted as being from 20hz to 20000hz.   Older ears will lose their ability to hear the higher frequencies over time  but not the lower.
Interesting comments from all. I see that a carefully chosen low frequency subwoofer can be potentially helpful. I have some Vandersteen speakers and I could supplement them with Vandersteen sub(s) as an experiment to see if I am missing something. Thanks for the responses.
@gdnrbob 
I am glad you are considering the Vandy subs.
Hi Bob, you responded to a second post that wasn't clear on its own.
I am not considering Vandy subs but rather I considered the Vandy M7-HP passive crossover, which costs about $2,500.  I probably would have already tried it except my main speakers do great bass (twin 9-inch woofers in a sealed, i.e., acoustic suspension, enclosure) down to about 40 Hz, so I really need to cross over lower than the fixed 100 Hz design of the Vandersteen passive crossover.  Currently, I am using twin Aerial SW-12 subs which sound great and utilize a remote control that can be used to easily adjust the output level for different recordings. 

I am considering adding a third SW-12 sub to the existing two, which are operated as single stereo channels and are placed in the front corners outside of my main speakers.  I will place the third sub along the rear wall or in one of the rear corners outputting a summed bass signal.  I cross them over between 40-45 Hz and keep my baseline output level (0 position) at a low'ish level to just fill in the lowest frequencies rather than to "shake the building."  IMO, if subs sound bad, this is where most sub users have made the mistake - the level is too high. I sold bass reflex (i.e., ported) speakers that went lower but excited room vibrations on about half of the recordings I listen to.  Adding one sub did not correct that situation but switching to speakers only going down to about 40 Hz and adding two subs absolutely corrected it.  Bass is now solid and controlled and rarely interacts with the room.

If I were starting over, and didn't already own the Aerial subs, I would look very hard at Duke's Audiokinesis Swarm Subwoofer System (four subs) as a reasonably priced alternative to obtain great bass.
Many do try to do just that. Look around however, it quickly becomes very obvious the hardest most expensive thing you can find is two quality speakers with true 20 Hz bass. They essentially do not exist. Turns out (read on) that for reasons of physics they cannot exist. Which is why they don’t.
@millercarbon
This statement appears to be false.


My speakers at home are made by Classic Audio Loudspeakers. They are the model T-3.3.


They have a pair of 15" woofers. One of the them is the TAD 1602, which has a free air resonance of 21 Hz. Are you really trying to say that a speaker like that in a properly tuned bass reflex cabinet (my speakers are the size of refrigerators) can't go to 20Hz?? They seem to have plenty of undistorted output at 20Hz in my room.




There are phase reasons to use subs but anyone who has to ask this question is not an audiophile anyway, and this poster is only baiting and so one worm is all you get...
Great subject. Right now I am in the process of doing room treatment and my bass sounds great. But I will still add 2 subs. I have demoed a few in my room and they really open things up.  My mains have excellent base, but the lowest of frequencies are missed and I want them also. Thanks for all the info, helps alot.
++++on adding subs.
I have one of my subs near a wall and under a window in my listening room, and when I want sound on the deck I put a pair of speakers in the windows with that sub. The deck specific speakers (old KEF Q10s...great sounding things) are powered by a separate amp (a trusty 100 watt Adcom) getting its signal from the main preamp, and the sub's signal is from the indoor mains little tube amp so I have to turn the window sub up a little...I have a volume control on the outdoor amp as it's way hotter than the indoor speaker's amp...all of this works very well, and unlike mapman I get my deck bass goin' which is good for the plants and lets my neighbors know I'm having more fun than they are. 
Full range cabinets are going to be rather large.  It can be much more convenient to go with smaller speakers plus a sub in a less conspicuous spot in the room. 

My understanding is that having the deep bass coming from more than one speaker invites phase cancellation.  

I assume that taking the deep bass out of the speaker handling the low mids and bass frequencies will help to make the audio clearer. 
@atmasphere 

Hello Ralph.

I see you use a SWARM system, so the sub woofer frequencies play in mono on a distributed basis. Similar to Earl Geddes approach/theory. Geddes argues for 3 to 4 subs playing the same signal to flatten frequency response at different locations in the room. I was wondering if you are using this approach for the same goal, for flattening at the main listener seat, or other?

I have a pair of 12" sealed subs playing mono and been wondering about adding one or two more with the goal of flattening at the main seat. Would love to know your take on this.

Regards 
Horacio

     Since bass sound waves behave so differently in any room versus midrange/treble sound waves in the same room and good bass performance is more difficult to achieve in any room versus midrange/treble performance in the same room, I'd suggest it makes sense to consider our system as 2 systems,a bass system and a midrange/treble system, and it's logical to deploy and optimize the bass system prior to deploying and optimizing the midrange/treble system.
     Starting from scratch, the best method for deploying and optimizing bass performance in any room that I'm aware of is a 4-sub distributed bass array system.  
     For those already owning high quality full range floor standing speakers that are capable of outputting accurate deep bass down to at least 20 Hz, however, I believe it may be the exception to the general strategy of getting the bass performance optimized first.  This is because these types of high quality speakers are unique since each speaker, in effect, already contains a high quality sub due to the exceptionally good deep bass extension of each speaker's bass section.   
     In these scenarios, I would suggest first positioning the floor standing  speakers to optimize the midrange/treble response as well as the stereo imaging at the dedicated listening seat.  Once this is done, the positions of the first 2 'subs' in your custom 4-sub dba system are established.  From here, it's just a matter of buying 2 more subs and positioning them in the room so that bass response is optimized at the dedicated listening seat. I even believe the 2 additional subs don't need to be of the same quality level or size of the main speakers' bass sections for the dba concept to work effectively. 
     This method is a bit of a compromise from a complete Swarm type dba system but I believe it will provide very similar results.  I believe this because the main dynamics involved in the very effective dba concept would still exist; 4 asymmetrically positioned subs with each creating bass room modes.  At the listening seat, the brain processes the multiple room bass modes (bass peaks and dips) by summing and averaging them which results in the bass being almost magically perceived as detailed, natural and smooth. 
     Voila, psycho acoustic principles at work. The dba concept absolutely produces the best bass performance I've ever had in my room and system.  I was initially very skeptical and I know just my words will likely convince very few but I also know even a brief demo would convince everyone.

Tim
Human hearing below 20Hz is described in this paper:
Hearing at low and infrasonic frequencies Moller H, Pedersen C S - Noise Health

Good site with audio tests including subs:
(this direct link also tells when you are hearing sub overtones- not good)
Low Frequency Harmonic Distortion Subwoofer Sound Test

In the end there is the human. For me a system reproducing music is sufficient
with 30Hz at -3dB. For electronic and movie sound effects the rotary sub might
be useful ;)
Rotary woofer - Wikipedia

PS. I stood once next to a 16Hz organ pipe and all I could experience was wind.

+1 @millercarbon The wide unknown is a fun place. Someone was asking about a cheap good crossover, check out Mini DSP. With a digital crossover you get exact slopes and have the option of doing room correction with Room EQ Wizard and can have even more fun with Multi Sub Optimizer. I prefer a Mini DSP with IIR over FIR filters as the IIR filters operate at 24/96.

I’ve heard my Magnepan 20.1 speakers full range with no subwoofers and they sound great. I added two properly integrated stereo subs and listened a year like that and it was even better. I added two more subs and measured/corrected the room and the “WoW” happened. Nothing is boomy, just accurate full range bliss. I don’t have to turn up the system nearly as loud to hear full range. In the end I’ve spent almost as much in subs as my mains which by all accounts are SOTA. That’s how important I feel the lower octaves are in music.
Jump on 2 subs asap dude!!
LISTEN to @hifidreams.  He knows what he hears, and it is all good.
This is a very timely topic for me as I am about to buy some new speakers. I have listened to both the Vandersteen Treo CT and the Quatro Wood CT at Audio Connection in Verona NJ. I was very impressed with both. These demos however were performed using John Rutan's house Aesthetix amps.
My amp is a Pass X-250.8. It is powerful and has very good bass control. I would love to bring it in and demo the speakers with my electronics but the problem is that it's so heavy to put in the car along with my pre and drive for 1 1/2 hrs to Audio Connection to do a more proper comparison between the two speakers. Also, my wife and I will be moving in a couple years when she retires so my listening rooms will change over time.
My two questions are:
1) Is it better to get the Treo CT and add a Vandersteen sub that can be positioned in appropriate locations as we move or just get the Quatro CT and not bother with subs?
2) What's the consensus on adding an AR REF 6 pre in the future to compliment my Pass amp, or could anyone recommended a different similarly priced preamp?
Thanks so much for any advice.
Bruce