What does a subwoofer solve?

I'm going to be very skeptical that the M900u is shy of bass.  Are you sure you didn't change anything else?? Speaker placement for instance?

Subwoofers usually have their own amps to drive them, and they are easy to integrate into a system. My Paradigms, at least, have several pots in the back to home in on what you need. Buy something like a stereo test CD and let your ears do the walking/talking.

Subs are meant for low freq extension. They "solve" nothing on their own.

Subs will make your entire system run better. They will lower the distortion in your mains when using a highpass filter. They will give your system more dynamic range (output). They will most likely add bass extension depending on your speaker. Subs done right are always better than no subs. 
 

not to mention you can place the subs for bass while not effecting the soundstage negatively. I can’t recommend subs enough but and a big but is you need a highpass filter to sound right. 

Your loudspeakers are -6db at 28 hz. I can't guess the 3db point but a good sub will be flat into the low 20s. There still is some information down there that is worth exploring. 

do you need a subwoofer ifd your source does'nt have the lows that a subwoofer would produce??

g_nakamoto

  I think that your question answers itself. 

 In my case, I was appreciative of the difference in performance that a good sub made. In a few recordings, I knew that the subsonic signature was there, but didn't experience it until the was in place. Yes, partially due to the fact that main speakers were not burdened with the task, but also because the information was there and is now being reproduced to a higher degree. 

I do not use any crossover to limit the main speakers. Instead, I play them out as far as they will go (Avantgarde Duos- older) and match the integrated woofers to the midrange for coherence. That means the speaker is bass-shy. I did a couple things when I moved from NYC area to Texas: I installed a pair of 15" sealed subs, tuned to match the integrated woofers in the Avantgarde (easy, given phase, gain and crossover frequency and slope)-- and not crazy expensive- Rthymik -: I also added DSP, on the cheap (DSpeaker 803_ II or whatever), It kills the peaks.

And it is improved by a change in cartridges- alas, that wasn’t cheap. Koetsu stone mo’fos. They have some seriously tonal, dimensional bass. I was using Airtights before, and LYras before that. As they say, -----

search bar is your friend...  this question *might* have been asked before, just maybe ... 😂

If you listen to rap I guess.. boom boom boom...subs are for home theater...never find one in my system, no way...my speakers go plenty low for me....

How many hours have you logged on the Luxman? Sure it’s broken in? 
 

Those BHK 300s look pretty beastly. Maybe they just have better bass control?

Properly integrated sub can sound amazing. Kinda difficult to get there but not impossible. If the room allows maybe consider a swarm type setup. Never heard one but from most accounts it’s a great way to get amazing evenly distributed bass. 

I too am skeptical that the Luxman doen't provide enough bass.  So I'll make a blind suggestion, which may not be the answer but is something to look at.

Every amp has different power requirements.  It is possible that whatever power cords, power filters, etc you have feeding your amp are adequate for the old amp but not adequte for your new amp.  If there isn't enough instantaneous power availble it will show first in the bass.  This has nothing to do with the nameplate ratings on the amp and conditioner.

Thanks for all of the input.  I found a local dealer who will let me borrow a pair of subs for a couple of days, so will probably take that route to start.

As to comments about doubting the Luxman doesn't have enough bass, I've seen it mentioned elsewhere, by other owners, that they too wish for a bit more in the bass.  Perhaps if I hadn't heard it right after the BHKs, I wouldn't know the difference.

But on several recordings, what was clear and dynamic in the bass on the BHKs isn't here with the Luxman.  I've had it almost a year, so completely settled by now. I made no changes to anything except swapping the amps.  The BHKs draw more power than the Luxman, so I don't think that's the issue either

lldd, 

PM sent.

Luxman M900u.  Very happy with the new amp, except for disappointing bass performance.

My experience with Luxman was the same. That was in the late 80's. I hated every minute with the Lux. It had no bass line , just a constant thump from the bass drum. And it didn't sound correct.. I  cringe even today when I see the name yet it seems to be popular. I think this is because there was a great push for midrange clarity back in the 80's at the expense of the bass. Indeed the bass was often over blown prior to that. And maybe the mids weren't as prominent as many are today. But  the problem with change is often the pendulum swings  to the opposite extreme.That's where we are today IMO

IMO, the question becomes can the subwoofer put out what is Not fed to it? NO. And if you have the same issue that I had, where there was very little to no bass line at all, then I don't know if the sub will give it to you.. I sold my Lux  within 6 months. Good luck

BTW a good sub will enhance all the frequencies of the music and make the main speakers sound bigger.

Dear @lldd : " BHK 300 mono blocks. The bass they provided for my Monitor Audio PL 300ii speakers was exceptional. ..................... Luxman M900u. Very happy with the new amp, except for disappointing bass performance. "

Well, both amplifiers are way different designs Where the BHK is an hybrid design with MOSFET output devices the Luxman is all SS design with bipolar output devices.

I think that you are comparing that " bass..exceptional " that in reaslity is more a colored/distorted sound coming from the BHK against the accurated and less " colored " Luxman design that between other characteristics play in pure class A for its first 12 watts that due to the Monitor Audio specs permits that you have in reality better sound with than with the BHK. Yes, I know that you like more that frequency range in the BHK but this fact is other kind of matters.

In the other side you are talking of " bass " in your speakers when the crossover in the MA comes at 500 hz and the speaker goes down around 32hz. It’s really dificult to to pin-point true bass range when the woofers/ports handle that really wide frequency range. Btw, you can play/test too with ports open/closed and the like and due that both amplifiers are so different you need to play too with little changes in the speaker position in your room: backward/foreward and its angles at your seat position you are accustom to. Even you can play too with changes in your seat position.

My take is that that Luxman is a superior amp but you are the best judge about because you know what you like.

Looking that wide woofer frequency range ( 32hz-500hz handled at the same time and those " long " excursion of the woofers say at 35hz affects directly to the remaining frequencies handled by the woofers: increment its distortion levels. ) that 500hz at the speakers crossover and other than the true bass frequency range adding a pair of powered subwoofers crossing at around 80hz using lo and high pass filters will improves the overall quality listening room/system against what you have to day and against with what you had with the BHK due that when you liberates the speakers woofers of bass frequencies below 80hz suddenly your main speakers will goes way lower in its today high IMD levels. This is the main positive contribution/improvement of subwoofers with the speakers you own and additional to that now you will have the true bass range handled by woofers and amps with dedicated units that were designed in specific to fulfill the true bass frequency range reproduction needs. Your main speakers will performs and shines better than ever, its clarity/transparency/dynamic/headroom and lower colorations will be amazing to listen it from top to bottom.Obviously you need a good integration of those subs where what you listen be a unity.

You do not mentioned if your system has a room treatment that almost always is mandatory for better quality performance levels.

Regards and enjoy the MUSIC NOT DISTORTIONS,

R.

My experience with Luxman was the same. That was in the late 80’s. I hated every minute with the Lux. It had no bass line , just a constant thump from the bass drum.

I can’t comment on something 40 years ago, but in my recent memory, of the past 3 years or so I’ve never ever heard the Luxman’s be bass shy.  The Luxmans I know of have extension in spaces both in the treble range as well as in the bass.  I am more likely to believe the BHK lacked treble, and that Luxman is more well balanced. 😁

But seriously, if the effect the OP describes is so severe it makes him want to suddenly add a sub I’m going to question whether this is really due to an amp swap. Room acoustic issues like adding more reflective elements in the room, or taking away bass traps are the sorts of things I’d suggest first. Next, if this really really is happening, swap your cables for some Mogami 3106s. On my Luxman I had to turn the bass DOWN after I put this cable into my system.

OP,

I think that it is great that get to audition a sub or two in your listening room. I am anxious to find what you think.

According to manufacturer specs M900u balanced input impedance 34 kΩ and BHK 300 mono blocks balanced input impedance 200 kΩ. If the preamp has high output impedance that may explains the Luxman doesn't has enough bass.

While @imhififan brings up a very probable cause, I can assure you that the BHK300’s don’t lack treble, or some other frequency anomaly.

I’m using them with a very revealing speaker, the TAD CR1.  I’ve never heard the speakers sound better, even against TAD’s own electronics (though that was from models ago)

Just curious why you got rid of the BHK’s?  Especially with some tube rolling, they are an amp I don’t believe I’ll ever get rid of, and know of one person who thought they sounded better than his Constellation amps, which were also designed in part by Bascom King, but are fully solid state.  Perhaps someday an amazing GAN amp with tube input stage may better them.  
 

Brings more problems than benefits. Get a good full range and use the sub for HT only

a properly matched system will not make you aware of "missing bass" 90% of the time, but i have at least 3 pipe organ recordings that are fairly palpably loud below 20 cycles per second [locks the air in the room with a vigorous pulsation of air pressure] that NO standalone stereo speaker system i’ve heard can touch, not even Snell type As or KEF 105.2s with monster amplification. for those 3, a great sub is MANDATORY. i know of a retired doctor whose large house contains a massive digital pipe organ - to reproduce those 32’ contra bombarde pipes he uses 8] twin-12" acoustic suspension subs in massive cabinets. that amount of speaker enabled the visceral pulsating room-shaking sensation of real 32’ organ pipes to fully manifest.

It is very unlikely that any hifi source will not provide enough base, bad base perhaps.  An amplifier may well be bass shy or lack bass control and certainly speakers are likely to have the biggest effect.  However a vital component affecting bass is the room. I have a small(ish) room with smaller floor standers and a 150 watt per channel hybrid power amp.  No source problem, no amp problem, no speaker problem but huge room problems. In the end stereo subwoofers and a minidsp have solved it, together with lots of room treatment.

Most likely issue is the room/speaker placement. Maybe no need for lots of purpose-made room treatment if you can move a few things around and there are not a lot of hard/shiny surfaces in the room. 

Keep in mind that we listen to our systems THROUGH the room.

Thanks again for all of the input.  I'll stand down on the subs for now and investigate some alternative placement of the room components, especially speakers.

One example of what I mean when I say they amp is shy on bass is Max Richter's Blue Notebooks album.  Second song (On the Nature of Daylight) just after the 1:30 mark on the song there is a sustained series of deep notes that you feel as much as hear.  With the BHKs, this was very present and audible.  On the Luxman, it's there, but barely.  This example translates to various other music.

I ditched the BHKs due to quality issues.  Three sets and they couldn't send me a pair that worked as advertised, so I gave up.

One more thing: The front end is a Linn Klimax DSM Katalyst (I know I'm in the land of mostly Linn haters here, but I can live with that).  Output impedance is listed at 300 Ω.

If you mean,’" What potential problems can a sub-woofer solve with regard to sound?" I would say many. And I would say in my own system, when properly integrated they supplement the low frequencies and allow me to hear lower frequency sounds. They add and enhance those lower frequencies because the sub-woofers I had chosen are flexible and designed to do just that. They can add lower level detail and allow my speakers to simply produce the frequency range they are designed to reproduce. I also think the allow my amplifier to work easier. in the end it’s a matter of your flavor of equipment and sound. Sub-woofers are just another way to get quality sound. But not always the best way. BTW even full range speaker systems have been known to benefit from quality sub-woofers. IMHO

If you don’t have at least 1 - 2 subwoofers you are missing a lot of low frequency energy that you didn’t even know was present 

fiesta75,

"If you don’t have at least 1 - 2 subwoofers you are missing a lot of low frequency energy that you didn’t even know was present ". There are no absolutes in audio. Not too long ago I was a big proponent of using dual subwoofers, not just for bass, but I experienced improvements across the audio spectrum. I recently changed amps and in my system/room I prefer  my system with the new amplifiers, minus the subwoofers over my system with the old amp and dual subwoofers. Based on my experience, I may never own subwoofers again for 2-channel.

Some manufactures of exotically large speaker systems and even some of those who include self powered subwoofers within their speakers often display them with outboard subwoofers. The location of the speakers optimized for the listening position is quite often in a rooms null which can choke the low frequency response. Adding outboard subwoofers in the rooms modes is the solution. 

A host of individually unique room issues can easily be solved depending on the flexibility and level of control of low frequency processing which is not generally focused on by this community. 

@m-db "A host of individually unique room issues can easily be solved depending on the flexibility and level of control ..."

100% agree. And I've experienced it first-hand with a DBA. Getting this right brings a night and day change. It is that big. 

I will say adding a sub done RIGHT makes a huge improvement in not just rap.  Getting to mix right is no easy.  I ended up with the JL Audio CR-1.  Not cheap.  But since the intro digital music a good external cross over is getting hard to find.  this did HT integration as well which was another Issue I had.  

I do have a BHK 250 recently upgraded from Krell KAV 2250.  It does have much more impact than the krell.  

I think you will find adding a sub especially if you can get the load of the mains with xover you will find it works so much better.  

May I ask what PS Audio could not get to work as advertised?

Some of my observations on using subs, in bullet points:

*It highly depends on your expectations, on how you listen to, and what you listen for.

*If you are looking for power delivery and just more (deeper or stronger), the sub will give that to you.

*When the sub amplifier is quite different from you main amplifier(s) driving your main speakers, on the long run this will cause a disconnect, and you will feel the strong urge of the upgrade bug without consciously knowing what drives this need.

*Adding a sub often compromises the harmonic structure of the music.If you listen for violin, piano, cello, then this might be a huge issue. For most people this goes unnoticed (or is not a priority at all), but if you are one of those (like me) that tone and timbe & violin means everything, then you might end up like me (never found a sub that integrated well - they did good things for certain material, but on the long run they failed at what I want most: natural tone).

*Be extremely careful with subs, just because we can, we always set them at higher levels than needed. There's the temptation, and I have not seen any of my friends deny extra bass..... result: unequivocal decline in hearing faculties. Of my longtime audio friends (been on the audio journey for 20-40 yrs), those without subs all have keen hearing, usually quite better when they were young, and the sub users had massive hearing decline.

*Even when you set the sub level (and resist temptation to boost bass), it will still increase listening fatigue. 

*Room / loudspeaker placement / amplifier matching is everything. Want better bass? Work on these, and it will give the most natural fully integrated sound. Adding a sub is a quick shortcut around these issues, and only you can tell whether it worked for you, or you need to take the long road.

Any choice you make, you will learn from it, and will enjoy it tremendously. This is all fun, and a great experience. Just be VERY mindful of your hearing faculties. You can undo any change to your stereo gear, but you can't undo damage done to your ears.

A subwoofer compensates for a human ear’s reduced sensitivity to the bass frequencies as demonstrated by the Fletcher & Munson curves.... as was the 'loudness' control of the older vintage amplifiers.

Perhaps try an amp that doubles down in wattage from 8 ohm to 4 ohm. Then again to 2 ohm. There are not a huge amount of options out there but there are a few.

I just cannot understand how a single speaker can help to improve my appreciation of the stereo sound. I have tried a subwoofer and all it did was confuse me.              I have two Audiolab mono 8300 amps. I use a Naim dac to organise the sound and produce a very good system. My Aria 926 speakers do a good job and the stereo separation is wonderful. However, when I add a sub-woofer, the sound is confused as all of a sudden , I can`t tell where the sound is coming from. To me a sub woofer makes up for the poor response that the speakers do in low frequencies. But when you add just one extra speaker, the result is ruined by a lack of separation. I can understand 2x sub -woofers, but not just one. Can someone comment on this., as I just don`t understand the reason for one sub-woofer.

When I listened to my system without a subwoofer I was pleased and could clearly hear stereo separation. But I had heard other systems whereby I heard much deeper frequencies in the music. In those systems I could not always place the lower notes/sounds/instruments but I was surprised I heard that musical information I was missing on my own stereo system. Once I bought one, then two subwoofers I had that same effect. But I do agree, at some point, usually when one spends over $5 to $8k you can get true full range sound from stereo speakers. I do agree with many people commenting here that proper integration with sub and speakers that play well together is key.

Assuming that a quality subwoofer is properly set up as it is added into your system: 

- it will 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 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

What does a subwoofer solve? That’s a good way to put it, ‘solve’.

The thing is, doing without subs is simply doing without the low register; it simply isn’t there, nothing bad added, so I can understand that some ask why use them, and I too did without them for a long time.

I chose subs for speed and accuracy, not boom boom, and went with the philosophy that says, it’s a stereo, so bring both sides up to spec, so to speak, to fulfill at least 20Hz - 20KHz: and more so, you can’t tell from which direction 18Hz is coming from, but one can sense from where the higher sounds emanate, where the subwoofer’s contribution syncs with the speakers, so two subs make the sync more accurate and thus the soundscape is more accurate.

Since none of my speakers go below 32Hz, a pair of subs brought the floor down to 18Hz.

What they ‘solved’: they contribute the content my system could not previously recreate; they enable the system to transmit more towards the total of the available information.

Adding two subs fundamentally transformed my sound: I’d been building the system for three years and all the care I’d put into it ‘bloomed’ into a higher perfection with them; I felt foolish that I hadn’t prioritized them earlier considering they were some time and work to hunt down, but didn’t cost much.

Before the pair, during the months when I had only one, it clearly helped, but never sounded ‘just right’; it sounded like half the promise of what two could do.

I have a very dynamic system that is in a long room with high ceilings my old speakers "Dunlavy 4's" did a good job with the bass extension.

I now have the brand new "Carver ALS" speakers they don't have bass drivers so a Sub is mandatory

I was asked to demo some "Sun-fire Signature 12" subs I have listened to the Golden Ear's they were very muddy I tried Rel not enough oomph I tried Velodyne they sounded good but a little pricey and they seemed very happy playing movies.

I brought home 2 of the12 inch Signature Sun-fires and was completely blown away my room has a lot of air to fill well let me tell you something those subs are angry! They have so much energy its like there alive! Now I have (4) subs I use 2 of them at around 40 Hz the other 2 around 80Hz, two of the subs are not the original Carver Sun-fires Bob sold the company and a company called "Core brand" screwed them up basically they de-tuned them for liability reasons the Signature puts out about 1,700 peak watts and that's why they are so responsive they have an enormous driver and with the design of the sub-woofer being a 12inch by 12 inch sealed box it takes a lot of power to make the driver push out but even more energy to pull back according to Bob Carver who has become a very good friend of mine he is so passionate about high end audio I love that guy.

I have not heard anything that touches the Sun-fire very tight deep bass the cabnet is only 12 inches by 12 inches they have a nice black finish on them so if you can find a set grab them also because they are older you would be smart to have the drivers re-coned there is a company called "U Robot" there online the owner is very knowledgeable and actually made some modifications to the driver that made a noticeable improvement for I believe $125.00.

I am very grateful I have got to know  Bob Carver he's intense at times after getting his new flagship speakers which he put a lot of time into I decided I wanted to play around with a digital crossover It required a quad amp set-up so I purchased the "Mini HD DSP" and added two more amps that I had it took some time and lots of patience but the end results were beyond my expectations I had no idea what I was getting myself into.

Bob's best friend Dave is very smart he gave me quite a bit of advice along the way he told me "your gonna be getting up and down a thousand times messing with that thing!" Well he was right I made adjustments for months and just couldn't get the high end frequencies to smooth out without killing the super highs those speakers like to play. Dave suggested I try a "Dbx 234 xs" analog crossover the Dbx is Pro audio equipment that's been around a long time its very well built and the price was right,

After playing with the Dbx for a couple of days the system came alive in a whole different way it is incredible, the high's that were very scratchy are silky smooth now.

I don't listen to vinyl I have a "Bluesound" streamer and use "Tidal" According to Bob Carver he says that "Tidal" streaming music is better than his $15,000.00 stylis Thats a statement for Tidal! The subwoofer is what ties the whole system together. The "Sunfires" blend into the system like there a part of the towers they are a very important part of the equasion I personally believe the more power the better the sub doesn't have to work as hard its cleaner and not boomy.

My girlfriend was taking a bath one day she didn't know I had returned so I downloaded an earth quake sound track! The track started out with alot of wind sounds then breaking glass with the house trembleing and I mean trembling it was kind of spooky down stairs I cant imagine what she felt upstairs lol all I know is she was calling my name with a very scared voice.

So my answer to the subwoofer question is try the sunfire Signuture!

Robert Purdy

Even for "full range" floor standing speakers, the optimal placement for bass response may not be the optimal placement to produce a big soundstage and clear imaging.  For the latter, you may need to pull them out into the room and away from the walls.  Unfortunately, that probably will reduce the bass response.  A sub(s) allows you to get it back (and then some, if you like).

["purdy, I tried Velodyne they sounded good but a little pricey and they seemed very happy playing movies."]

Do recall the model of the Velodyne subwoofers you auditioned?

After a decade of not knowing who designed the pair of Phase Linear 400's that I beat the crap out of in  a PA rack and sold in working order I became a Bob Carver fan. I'm enjoying is tube mono's right now and regret not purchasing a pair of ALS's.     

If your ever in Las Vegas look me up I will demo my system for you according to Bob's Carver wife "Peggy" Bob said the following day after being at my house "Peggy" said to Bob, "Purdy's system sure sounded good you better step it up!

I love it!

Your question is “What does a subwoofer solve?”

Answer: your midrange. If you can still borrow those subs, set the XO frequency between 100 & 110.  Yes, depending upon its F3 it can extend your system’s low end and [should] improve your low end’s SQ. 

I’ll wait for the tomatoes.  
 

Tony 

I've taken a somewhat unconventional approach to bass.  I have rebuilt Maggie 3.3s and they're actively bi-amped with a Marchand crossover and Krell on top and Classe on the bottom.  Then I have two REL Britannia subs running from the Classe. 

Just this biamp-2-sub setup sounds very good.  I don't find myself "missing" bass per se.

But on Friday nights after a couple beers I prefer my stereo to sound a bit more like a club.  So I have 2 DWM woofers (match the speed of the maggies -- these are not subwoofers) and 2 more subs - another REL and a Sunfire True SuperJunior, which is both very fast and has a nice sharp thump! if you want it. 

I run the signal to this additional bass subsystem through a DBX 120X-DS, which synthesizes additional bass at one octave lower than the sample for the 4 lowest octaves in the band.  Now this would crapify the sound if I rain the Maggie 3.3s from that signal, but I don't. Instead it's the second output from the preamp into the DBX box and then to the two woofers and two subwoofers. Don't crank the volume too much or the bass is overloaded...subtlety is better. 

With this, I can have a relatively "clean" sound or one that preserves the mids and highs of the clean sound but with a thicker club sound.  The DBX can make the subs growl.  

Subwoofers can solve a few problems (and create more), depending on how they are used. My preference is to use subwoofers to add pressurization to the room and ensure even response at the listening position. Even with full-range loudspeakers with deep low-end extension, the best place in the room for imaging is almost never the best placement for bass. Separating concerns enables the best of both.

This has probably already been said but a sub, or subs, can solve the problem of placement.  The best location for bass is unlikely to be the bast place for the rest of the spectrum. 

In my opinion the ideal situation is to have large speakers with big woofers that provide a lot of punch and upper bass energy, but that roll off the deep bass gradually starting around 80hz.  Speakers that have deep bass extension flat to 30hz almost always have negative room interactions.  These would be greatly reduced if they had a -3db point at 60hz and typical sealed box roll off.  The deep bass is ideally filled in by multiple subs placed where they provide the most even response.  Taking deep bass duty away from the main speakers and amps reduces distortion and the amount of power required.

Are you using a power conditioner? Sorry didn’t read every post. I own some PS Audio monos and it seems they prefer power conditioners to perform there best in my system. Cleaner bigger bass. I run passive conditioners. Some of my other solid state and tube amps the conditioners take away the bass and full presentation. With those amps I  go straight in the wall. The difference is not subtle.

I tried subs long ago, didn’t know how to dial it in so had to let them go, since then haven’t been a fan of subs. Maybe if I knew how to set them up I would have a pair now.

For those that have tried subwoofers in their systems and didn't like them, the usual reason for this is improper placement and integration.  They can take quite a while to set up properly and incremental changes can yield great results but could also make a mess of things.  Any easy was to visualize what is happening in the setup is to use a laptop and REW, Room EQ Wizard.  It's been around for many years and is quite a helpful tool in subwoofer setup. 

Keep in mind that without knowing how your particular room reacts with bass and your seating position, you could be chasing your tail for weeks or longer growing more and more frustrated with the setup experience.  In our last house, I spent a whole weekend setting up 2 subs in our family room, running dozens and dozens of sweeps in REW, each time altering settings in the preamp or the phase settings on the subwoofers, or the physical locations of the subs, volume settings, etc., etc. to get it right.  But once I had that done, with the subs properly married to the system and the room, it was fantastic.  You just can't plop a subwoofer or subwoofers down any old place in your room and expect good results.  Patience is key to unlocking what they can do for you.