[dket]

In my X5's particular application the answer is yes.

To start with I have an open floor plan with the living room itself larger than 450 Sq. Ft. / 10 Ft. ceiling and opened to 3 other rooms with only 2 small separate backwalls totaling 44" wide.

I think we all can agree on that vibration is an enemy of quality sound reproduction.

In my case to get any decent bass required turning the woofer volume up to clipping levels (red Lt. blinking).  Any amount of clipping causes the baffle to vibrate a lot more than the midrange is doing.  Put your hand on the bottom of the baffle or mounting bracket.  You'll be amazed at what you feel, I certainly was.  Even turning the dial down to just below clipping, the bass woofer's vibration is still more than what the mid exhibits.

From looking at GR Research and Linkwitz speaker (which I was considering as replacements) design concept, I decided to add a pair of subwoofers to the mix.  I have a common single 15 amp circuit feeding my entire playback system.  I was afraid adding the subs would overload the circuit with the X5's power requirements.  But, everything worked with no issues.

After tuning the subs and the X5's setting down to 1 notch above the 1/2 mark, I'm now a happy camper.
I'm hearing not only greater bass but a more fuller, detailed, musical presentation from top to bottom.  The baffle's overall vibration is now, I believe, the lowest it can possibly get.
 
P.S.  a great album to listen to for bass analysis is "Ten New Songs" by Leonard Cohen

[morganc]

I had the same experience with X-5's in a large apartment and now have X-3's in an open floor plan and am considering Sub options. Which ones did you choose and how did you go about the integration process? 

[dket]

Morganic, I'm using the small GoldenEar's SuperSub X subs left over my previous Magnepan's 1.7i's days.
You definitely need pairs for best sound resolution.
There are a lot of videos on you tube for setting up sub pairs.  Every room is different.  The biggest thing is not having them pointed at same area on the same wall.  The more diverse reflection the better the implementation. REL Acoustics has info on setups.
Speaking of REL, they have their T/9x's on sale right now which are winking at me.

[Tyson]

I have the X3's in a 2500 foot split ranch home (semi-open floor plan) and for the large majority of music I'd say no need for a sub.  But when I listen to something like electronica or hip hop at high levels, I'd say yes. 

[morganc]

Morganic, I'm using the small GoldenEar's SuperSub X subs left over my previous Magnepan's 1.7i's days.
You definitely need pairs for best sound resolution.

Yes am looking at a pair of GR Research Triple's!  Going big!

[morganc]

I have the X3's in a 2500 foot split ranch home (semi-open floor plan) and for the large majority of music I'd say no need for a sub.  But when I listen to something like electronica or hip hop at high levels, I'd say yes.

Thanks Tyson, that is about what I have sf wise and yes on most music no need at all, and this is certainly borderline gluttony, but I believe that extra bottom end will be better than any other upgrade I could make. I have positioned the speakers well so far, eliminated nodes, and boy it is sounding great.

And I can get a used pair of the Triple GR Research already made in white to match my X-3's for the same price as the kit would cost and I am not a good painter!

[Tyson]

Thanks Tyson, that is about what I have sf wise and yes on most music no need at all, and this is certainly borderline gluttony, but I believe that extra bottom end will be better than any other upgrade I could make. I have positioned the speakers well so far, eliminated nodes, and boy it is sounding great.

And I can get a used pair of the Triple GR Research already made in white to match my X-3's for the same price as the kit would cost and I am not a good painter!

Nice!!  Yeah triples in matching white would be a very big upgrade.  In my downstairs system I have the GR Research Super 7's and those use double servo OB subs, and the difference in low bass slam and quantity is substantial vs the single 15" woofer in my X3's.

[morganc]

Yes agreed Tyson.  How much of a challenge if any will it be to integrate the subs ? 
My partner loves the idea (she's a keeper!) and my only hesitation now is on the integration question.

[Tyson]

Yes agreed Tyson.  How much of a challenge if any will it be to integrate the subs ? 
My partner loves the idea (she's a keeper!) and my only hesitation now is on the integration question.

The simplest way is to run the subs in parallel with your speakers and just let them fill in the low bass between 20 and 40hz.  If it were me, I'd also build a small in-line filter to put between my preamp and my main amp (a single capacitor is all you need) that would cut the really low bass from the X3's. 

Nice video explaining how to make an in-line filter - https://www.youtube.com/watch?v=65eFr2rKy3M

[dket]

I just use a spare of set of RCA output outlets from my pre amp for the subs.

[Early B.]

I have the X3's in a 2500 foot split ranch home (semi-open floor plan) and for the large majority of music I'd say no need for a sub.  But when I listen to something like electronica or hip hop at high levels, I'd say yes.

Even when you think you don't need subs, you need them. Add more OB subs and you won't go back. Remember -- subs do a lot more than fill in the low bass.

Similarly, you often hear audiophiles say, "Since I have high-efficiency speakers, I only need a few watts to power them." Higher power is doing more than feeding your speakers. Not always, but often you can literally hear the benefits of higher power.

So the real question should be -- "Will adding more subs improve the overall sound quality?"

[Tyson]

I just use a spare of set of RCA output outlets from my pre amp for the subs.

That's what I meant to say, too.  One RCA output goes to the sub and one RCA output goes to the main amp.  The RCA output going to the main amp, I'd put an in-line filter there so the main speakers don't produce any bass below 50hz. 

[morganc]

Got it. Thanks makes a lot of sense with the in line filter and yes I've been thinking the same Early B:   This will create a massive improvement across the board.   

[Tyson]

Got it. Thanks makes a lot of sense with the in line filter and yes I've been thinking the same Early B:   This will create a massive improvement across the board.   

Are you still running the Don Sachs preamp?

[dket]

Not being a wiring techie, the pot adjustment on the X5 bass works for me.  I got rid of that awful baffle issue and got better sound at all volume levels.

[morganc]

Are you still running the Don Sachs preamp?

Yes and he made it for me with an rca out for a sub

[Tyson]

Yes and he made it for me with an rca out for a sub

Well, there you go

[mrotino332]

I'm in an odd room in the basement 11 feet wide, 6 1/2 foot ceiling and 21 feet long so medium room and have my X5s on the short wall five feet out. 
I did previously use two rel storm III subs with my previous monitors in stereo mode, speaker level inputs and was happy with the bass quality.  But when I received the X5s I definitely preferred the bass quality with the X5s alone as compared to running them with the two rel subs.  In my setup with bass traps in all four corners the bass with the rels was not as fast and detailed as just the standalone X5s.  I've found I prefer the open baffle bass signature and do have the bass knobs up near maximum on the plate amps but have no issues at that level and am satisfied in my size room.  If I ever move my system to a larger room I would consider open baffle subs but not box subs.

[Bingenito]

Everyone has different experiences however and I have made this mistake myself.

What might seem like the need to add a sub or 4 is at times due to speaker placement relative to walls and distance to your listening position being in a null. I would try to walk around with a consistent bass track playing and see where you have much more bass (likely peak) and then where the bass sounds the most accurate. See if you can move your chair there (slightly closer or slighter farther away) 6-12" can make a difference and within 4ft you might be surprised.

Advice like this is often ignored because people love the idea of buying new gear but it is like having an injury and thinking that an anti-inflammatory is the cure... nope just masking the issue. When the new subs hit the room you have to overcome the same issue so get it right with the main speakers first.

[lazbisme]

how about placing the subs in the listening chair and crawl around on the floor until you find the "best" spot for the subs?