Help with choosing sub-woofers please

Having survived more than 30 years using full-range electrostatics @clearthinker has finally decided to get sub-woofer(s).  Previously he was put off by the well-known difficulty in setting the cross-over to allow a seamless integration.  Modern sub design and electronic aids seem to have fixed that.

@clearthinker is pretty knowledgeable and experienced in most aspects of two channel audio. He has spent some hours researching sub-woofers but he's having trouble evaluating the benefits of differing design and application approaches.  Such matters are not dealt with qualitatively or comparatively in most postings and videos.  He has yet to listen to any and will be trying contenders in his system.  But it needs to be narrowed down as he can't try them all.

His Martin Logan CLX Anniversaries are -3dB at 56dB and driven by vintage Krell 200 KRS References.  The room is 23 x 15.5 x 8.5 feet, carpeted, plaster ceiling, All walls are deadened with French style fabric covering and 25mm of wool behind.  Symmetrical, no windows.  No furnishing save equipment, two chairs and a small side table.  Subs will be spiked to concrete floor.  @clearthinker  listens to two channel stereo all genres, no theatre in this room.  Cost is not the most critical issue.

Some of the issues that need evaluating (in no particular order) are:

*  Benefit of subs using two opposing drivers to reduce vibration, rock and roll

*  Floor firing vs. side firing

*  How much does size matter?  Small is better if all things are not too unequal

*  Benefit of two subs to create stereo image.  Many say bass isn't very directional below about 50Hz.  But bass heard above that on the MLs is certainly directional

*  To what extent will the sound deadening deal with room modes?  Some say bass waves go straight through wall treatments back to the hard surface behind and bounce right out again

*  Benefit of two subs (or more?) optimally arranged to cancel room modes.  The unlamented Miller who was rude but knew a fair bit about audio used to mention six and eight.  There is freedom to locate.

*  Taking unit price into consideration, is it better to have one hi-end sub, two decent ones or multiple smaller cheaper subs to deal with room modes?

*  Do wireless feeds work well or is good old wire better?  How much does wire  choice matter in feeding subs (that may be a long way from the amp.  Incidentally the Audio Research Ref 6 is fully balanced.

*  Is the KEFKc62 too good to be true?

*  Does it make sense to keep it simple and just to use ML subs and digital set up systems with ML main speakers?  If so, is it worth spending more to get the Balanced Force series?

*  What about REL?

*  Anyone else?


Thanks in advance for all your posts.  I'm hoping a discussion of qualitative and comparitive issues  will help others get to the bottom of optimal sub-woofer applications.



IMO the little kef sub(s) would run out of steam in your room. If you end up comparing those to a pair with 12" drivers I think you would hear how the small drivers just can't sound effortless in a good sized room. Same with the rel micros.

My room is smaller and probably not a good comparison, but before a storm knocked them out I had four subs,two 10" and two 12" SVS sealed subs (plus GIK panels) and they did indeed eliminate the worst room mode.Nobel100 who doesn't post much anymore, was my biggest influence to try that.

 Now I have two HSU ported subs that are almost perfect for me. The two things that are lacking are DSP and the ability to vary the phase in increments.Blending them in is simple but they need even more fine tuning. When the low and mid bass are just right regarding tone and texture the vocals are too textural.Tuning it back until the vocals are natural the bass suffers.IME wires and pcs don't seem to make a difference.So now I'm thinking one or two more with DSP and variable phase or start again. Anyway I'm looking forward to the responses here and what you ultimately end up with.

 The Balanced Force subs seem like a great option if you're sticking with ML.

Earl Geddes on Multiple Subwoofers in Small Room

This is from 2013 so the software has probably  improved but the theory is still very relevant.  According to Mr. Geddes the improvement of over three subs in minimal but the improvement from 2 to 3 subs is substantial.


Taken from a thread on another forum- my experience and continued enjoyment with a pair of REL t9i subwoofers in a room of similar size to yours- 

"REL T9is are tuned and ready to review.

Let me start by mentioning my experiences as they relate to common thoughts about REL subwoofers (myths vs. reality) as they apply to these T9is in my room and system.

Common thoughts-
REL subwoofers cannot play deep. MYTH. These T9is are measuring flat to 20Hz at the listening spot and play deep and sustained quite well.
REL subs are musical, fast and have good tonal definition, low distortion and emphasize quality- REALTY. So far I have heard many shades of bass and the notes are well presented and represented with dexterity. Zero bloating, bleeding and sluggishness.
REL subwoofers are easy to setup and integrate because of their quickness. MYTH. If you really care and pay attention to the sound, they are no easier to integrate than any other subwoofer. Proper technique and process are still required- however they are quite "integratable" even without variable phase control.
REL subwoofers are not punchy. MYTH! These t9is are punchy as heck !
REL subwoofers are a poor value. Leaning to MYTH. So far they sound better than any other subwoofers I have heard or owned and are a perfect compliment to my system. Previous subs include JL Audio D110 and Martin Logan Dynamo 800X. The RELs beat each of them easily. It seems like you get what you pay for. Note- I have heard but not owned SVS subwoofers so I cannot comment on their value. Right now I have no interest in them based on the sound I am hearing which is excellent.

Final comments- they do not harm the midrange! The clarity and transparency I have without subwoofers is still there with the subs engaged and tuned properly. Unlike previous subs I have owned.
I love the sound and they are keepers". 

Interesting video, thank you.Hearing instead of reading the facts and theory was really helpful.

Many say bass isn’t very directional below about 50Hz. But bass heard above that on the MLs is certainly directional

* To what extent will the sound deadening deal with room modes? Some say bass waves go straight through wall treatments back to the hard surface behind and bounce right out again

At 80Hz the waveform is 14 feet long.

The ear cannot know the sound is there until the entire waveform has gone past it.

It cannot sort out the frequency until 2-3 more iterations. By this time the waveform has bounced off of the rear wall (unless you have an enormous room!) and is making its way back- and has probably already passed the listening chair by the time you can even tell what the bass note is.

So in most rooms anything below 80Hz is entirely reverberant. So its not directional at all at 80 Hz, let alone 50Hz.

The other takeaway: if you have a room with the wall in front being roughly parallel with the wall behind you, there will be standing waves no ifs ands or buts. This is why there can be good bass everywhere in the room but the listening position, and this cannot be treated with room treatment or room correction.

If a standing wave is cancelling bass at the listening position, you could put 10,000 watts worth of correction at that frequency and it would still cancel.

This is why multiple subs (Distributed Bass Array) works. If properly placed (asymmetrically in the room) they will break up standing waves, resulting in evenly distributed bass throughout the room.

Audiokinesis makes a subwoofer system called the Swarm that is 4 subs meant for this purpose. Unlike most subs, they are designed to sit directly against the wall, taking advantage of the room boundary effect. This allows them to be more compact and easier to place, especially if space is limited. I have Swarm subs in my system- they work a treat!

The trick is to keep their output below 80Hz so they don’t attract attention to themselves. Stupidly easy to set up too.

How many times do we hear this one?

((((They need a VERY large room. Most homes don’t have the kind of space they need. They sounded best out a good ten feet from the back and side walls.))))

One of the best solutions we have found is a pair of Vandersteen Sub3s

They offer a unique solution for every room with its non DSP adjustable analog tuning from 22 hz to 130hz on each channel. One of the Martin Logan dealers at the time ran a pair of Vandersteen High Pass filters and Vandersteen Subs achiving fantastic results and got best sound at show with CLS. We have also sucsessfully paired many pairs of Vandersteen subs with Magnepans and other planar speakers

Taking full advantage of their unique High Pass/ bi amping allows lower distortion in the main panels or any speakers, dramatically improving the clarity and transparency of the whole system, while tuning out unwanted heavy bass that overloads most all rooms. This for me has always been the best solution. .

Best JohnnyR

Audio Connection

Vandersteen dealer

and if you want, you can always swarm the vandersteen subs. Also, it’s Stereo 101 to NOT place the listening chair in a mode…..

When housekeeper moves my chair back 6” towards the wall, my ears let me know she has been here…..

Best to all


Thanks y'all.

@danager     Early in his vid Mr Geddes says damping all the room boundaries is good for bass.  Then just after 17m he says it won't do any good at all.  Kinda put me off him, that and his whiny voice and condescension, including to members of his audience.

@avanti1960    Methinks you protest too much about REL.  They are good subs and already on my shortlist.  Do you represent them at all?

@atmasphere   The Swarm looks interesting in principle and good value.  Putting in 4 subs to cancel room reverberation is a bit like herd immunity.  I suppose 'herd' = 'swarm'.

But why are they two feet tall?  What's the other half of the cabinet doing?  They're not really 'compact' at 23x12x12 inches.  Why do we have to have old-fashioned wood veneer finishes?  Why don't they quote the frequency range between dB limits?  And, as @tomic says, any small sub can be 'swarmed'.

@atmasphere   The 14 foot wave takes 12 milliseconds to pass my ear.  Is that fast or slow?  My MLs are flat at 80Hz and the bass there is pretty tight, not an unrecognisable reverberating mush.  What's more I can hear it arriving from its source on the soundstage.  I await to hear how much worse it gets at 25Hz.  And whether it's really true my room boundary damping won't make any difference.

@audioconnection    What is it about the design of the Vandersteens that allow them to behave so differently as a stereo pair with essentially the same control systems?



Yes this video was more like the ones we record at our DIY meets but I believe he was talking about constrained layer dampening for bass which according to his comments later in the video do provide bass dampening.

This video was from 2013 almost 10 years ago. Before you make a judgement you should know who this guy is. Dr. Geddes (PHD in acoustics) has done extensive research, real scientific research on how we perceive sound, environmental reaction to sound and wave guide design. He and his wife worked together to design experiments to actually measure perception. I just saw another video regarding THD and how our perception of it varies at different volume levels and what harmonics we can detect and which ones are masked by the way our ears work. This reinforces my theories that measurements don’t really mean that much because we’re measuring the wrong stuff but I always like the people who agree with me more than those who don’t.

Dr. Geddes is now out of the stereo biz and makes stained glass windows but I bet his stereo sounds really good while he’s doing it.

Cheers, and good luck


Quested Subwoofers from the UK, Studio Accuracy at its best and easy to intergrate using a analog crossover control or DSP if you into DSP.

I added a second Rel this weekend and I'm very pleased with the improvements in in the depth and smoothness of the bass. Seems like the whole soundstage is more cohesive. I was going to sell my speakers and single sub and buy speakers with built-in subs but what I was interested in weren't available to listen to. Good for me. Too bad for them.

@danager   Thanks.  Yes near the beginning of his talk he said he has an acoustics PHD.  Most of what he said makes sense, but he was totally contradictory on the benefits of conventional room boundary damping for low frequencies.  My room is built so I can't alter it now.  Looking into constrained layer damping, it is said the effect is gained by attaching two different materials to each other, even though these may be relatively thin.  Other vids have suggested that short of mounting walls on springs (not very practical, it is impossible to damp low frequencies.  One said you need 5 feet thick material to damp a rear wall.  Not very practical either.

@dalims4     Noted.  Did you wire the two RELs separately for stereo or wire both sides into both?   And where did you site them in the room?

@clearthinker you are correct regarding passive bass dampening it's not a practical  strategy.   Nelson Pass made an active dampener that would listen and then apply a 180 degree phased mirrored sound to compensate much like noise cancelling headphones but it either didn't work or was never marketed correctly but I like the concept as it could easily be place in the rear of the room without the hassle of running wires or futzing with wireless connections.

I now read in an REL spec that their wireless has’ delivery latency’ of 16-20 milleseconds.  Wonderful term ‘delivery latency’.  Might sound benign but it just means ‘delay’.  A 20ms delay is the equivalent of the length of a 50Hz wave, or around 25 feet.  So the sound takes 20ms to get to the speaker and then perhaps another 10ms before it gets to my ears.  The kind of digital tech we don’t need thank you.  OK perhaps for the end of the world on a video extravaganza; I don’t mind if the end of the world is delayed 20ms.  But not for a symphony thanks.  Not just with REL who are honest enough to give this spec; the tech’s all the same so I guess they’re all like that.

Pity, I had been thinking of the benefits of losing the wires/cords to 3 or 4 subs around the room.  But a signal travels along a wire at nearer the speed of light.  As someone said, no such thing as a free lunch.  Especially with digital, I said that.

Hell, this is even more complicated than I thought.

They’re wired separately for stereo through the high-level inputs and set inside the speakers facing each other pushed close to a hearth.

The 14 foot wave takes 12 milliseconds to pass my ear.  Is that fast or slow?  My MLs are flat at 80Hz and the bass there is pretty tight, not an unrecognisable reverberating mush.


Don't worry about the speed- that has nothing to do with it.

You don't hear reverberant bass as mush! In fact it might sound quite taut, like you are already hearing at 80Hz (that's reverberant as well)!

You'll have to ask Duke why he did it the way he did. But having played with a few subs I find that if you want them super small if they go down to 20Hz they won't be capable of much dynamic range, or they simply won't go anywhere near 20Hz!

Buy a pair of XLR cables from Mono Price or Blue Jeans cables long enough to circle more than half way around your room. When the cables arrive order at least two sealed app equipped SVS subs which come with a convenient free trial period.

Use one of the subs to Crawl Test map your rooms loudest modes. Locate a sub in the loudest two modes. Follow the manufactures instructions for multiple sub usage. In no time at all you should have a good idea of what suits your low frequency taste.  

Subwoofer remote control = fun. 


2 is better then 1,

4 is better than 2

6 is better than 4

8 is better than 6


:-)  good luck

Hi @phantom_av   Are you selling 'em?

More interestingly your post suggests there is a problem with odd numbers.  Perhaps irregular formations will cancel standing waves more effectively.  In which case an odd number of subs would be good.

@m-db    You and others advocate the crawl test as if all standing waves are bouncing around along the ground.  Surely they are present throughout the room, in which case we should also test whilst standing?  Would save my knees as well.


no affiliation with REL or the audio industry.  after trying several subwoofers and never able to fix their integration issues to my satisfaction i decided to try REL. they did the trick.  

it took a few weeks instead of months to integrate them.  

they have solid enclosures that do not resonate and color the midrange.  they play deep enough, they are fast and their bass has a nice quality- not too fat or not too dry,  just nice and right.  i also like the crossover and level click stops so you can log your settings as you fine tune.  

just keep them at least 12 inches or more from any walls to avoid peaks and you will love them.  excellent for music which is all i play.  peace. 

@clearthinker the "crawl"  shows you where the bass sounds weak and where it's stronger in your room. It can be heard while standing close to the walls too.When you find the spots that are strongest getting down close to the floor finds the exact spot where the bass is tightest and not muddy.In my room there are two corners with bass build up and the two other corners have nulls.Out of curiosity I placed subs in the spots with the weakest bass firing towards the hot spots,which didn't work well at all. What sounded best to me when I had four subs(sealed) is when the best spots were located, was to place the subs there firing towards the wall.

  The two HSU subs I have now are a different beast and sound better placed along the side walls on either side of the listening position, left firing towards the back corner, right firing towards the front corner(hot spots) with both ports open, Q set at .3,crossover 40hz.Possibly because the steeper slope matches the slope of the speakers. I didn't like the sound when both were sealed or even one of the ports were open.Surprised me, but I'm glad I chose them for the multiple settings to experiment with. I enjoy the tweaking,so I find the thought of the SVS subs with the app intriguing to be able to change the settings from the listening position.



I'm not sure that's true.


2 is better then 1, 4 is better than 2

is true 3 is almost as good 4 properly placed and EQd beyond that its just spending  money that could have been spent elsewhere for to actually improve the sound.

If you wanna do it right and your room/budget will allow, do a swarm as @atmasphere recommends.  It’s the gold standard.  If that’s not in your budget, get a pair of SVS SB1000 Pros that offer integration software and will help deal with room modes better than one bigger sub.  I also agree with @audioconnection that Vandy subs are awesome, and if you can get a couple of used 2Wq subs you’ll have an awesome experience for both music and movies on the cheap.  FWIW, and best of luck. 

Rather than a wireless sub and dealing with the network delays and active bass trap would effectively kill the reflection node


Post removed 

Whilst picking up the really helpful comments from all who responded, I have also been continuing my research on the net.  I think I have made some progress and am ready to do my first set up and listening trials if I can borrow the kit.

@jtcf     Thanks for your post earlier.  I am not sure you're right the KEF KC62 won't deliver the goods in my room.  There's a lot of new tech in there.  I've read four pretty positive reviews.  The fullest is at in Australian Hi-Fi, an offshoot of the UK mag What Hi-Fi.  This describes the technical innovations in some detail, which include two co-axial drivers and a cast aluminium box said to be very rigid - easier to make it rigid at this 10 inch scale. 

As to output it is true the KC62 is limited to 115dB and won't often be able to deliver all that.  But I will be listening to music only at reasonable levels, not cinema, so I certainly don't need gut-sickening boom.  There is 1000w of amplification to power its two small drivers; that should be plenty of volume for what I need.

One thing that alarmed me at first with the KC62 is that KEF claim it goes down to 11Hz.  This didn't seem possible for this very small size.  Nor do KEF specify how far down the output is there.  But the Australian reviewer did a lot of testing and publishes five graphs.  In the main one the frequency response is plotted for each of its 10 roll-off rates.  For rates between 40-60Hz - I am likely to start with 60 or 70 - the output at 15Hz is down only 8-9dB.  At 20Hz it is only 2.5dB down.  Even compared to much larger subs this is superb.

The KC62 has two co-axially driven drivers, mounted in opposition.  Two drivers firing 180º from each other not only damp vibration and rock and roll.  It also seems to me they will be capable of better room mode cancellation than a single driver.  I am going to start by trying two KC62s.  As well as experimenting with location, turning the orientation of each in each position should offer a lot more variability to experiment with.  If two work well over extending listening, then I may try adding one or two more.  Whilst not dirt cheap (R&D has to be paid for) these are priced at only about 40% of the Martin Logan Balanced Force, where I wouldn't really want to pay for more than two.

At just 10 inches cubed, probably in white not black, even four are not going to get in the way or degrade room aesthetics too much.

I will be reporting back and sharing.

One thing that alarmed me at first with the KC62 is that KEF claim it goes down to 11Hz. This didn’t seem possible for this very small size....At 20Hz it is only 2.5dB down.

Uh, yeah, I’d check that. If the company doesn’t specify a -3dB lower level, well, there ya go. I’d just say you can get a pair of SVS SB1000s that will get you down to an honest 20Hz for under $1000 for the pair. And, they offer a generous and truly risk-free, in-home trial including shipping both ways . And, they also offer an integration software app — not sure if KEF offers that, but that’s huge. Lastly, SVS is a business based primarily on subwoofers — KEF, not so much. Best of luck.

Thanks @soix 

The independent test by Australian HiFi covers this.  It may be a a fair bit down at 11Hz (in fact -22dB on that graph), but I will certainly take 8dB down at 15Hz and 2.5dB at 20Hz.  As good as anything out there and better than nearly all.  No-one else quotes figures at 15dB.  Not that there's much to listen to down there apart from rumble on your old Thorens and Garrards, ho ho.

By the way, the max output is 105dB not 115 as I typoed  Sorry.  But 105 is plenty loud.  One reviewer says that is eviction level.  Maybe.

You are correct, KEF doesn't currently offer digital set-up.  Looks like I'll be crawling around a while.

I am in UK so don't get US deals on SVS.  Some reviews report that the SQ is poor on SVS.

Yeah, I'll let you all know in a few weeks.

[clear thinker]   You and others advocate the crawl test as if all standing waves are bouncing around along the ground.  Surely they are present throughout the room, in which case we should also test whilst standing?  Would save my knees as well.

Your absolutely correct. Crawl Test is a misleading term / title used to search the net for directions and examples. My subwoofer manufacturer suggests the test near the beginning of the setup procedure. 

In my limited experience I usually elevate one subwoofer onto a sturdy table or side table at the listening position. Using the sofa or chair should be fine. While playing my subwoofers included Sweep Tone CD simultaneously through the main speakers and the subwoofer I walk the room listening and making note of the rooms nulls and modes. I measure the modes slightly varied levels using a Radio Shack SPL meter. I found actually crawling the room will yield slightly varying intensities and locations that I consider overkill.

As a result my two twelve inch subwoofers are asymmetrically located in the rooms two loudest modes. They're mounted on MDF platforms with 2 inches of high density foam using extra soft rubber casters rolling on a suspended wood floor.

Since every aspect of every room and system is unique, like speaker placement the Crawl Test is simply a starting point that I've found indispensable for any new installation. Best of luck with your project.

I had been using a single 15" woofer for about 45 years, either sum L+R or just use R.  Neither are correct as each channel should have a woofer or more. The electronic filter for low pass was 36Hz at 18db per octave.  Full signal went to the Quad ESL 63.

Recently I replaced the single woofer with two JL Audio E112 subs.  The important points here are there is a woofer for channel, the sub has a built in low pass filter currently set at 50Hz, and the signal to the main speakers has a passive high pass single order filter, 3 db down at 80 Hz.  Perhaps other crossover frequencies would be better but that is what I have.  I tried the high pass filter in the E112s, the flexibility would have been nice, but the ESLs are not forgiving to E112 electronics.

You will likely need test gear to setup subs. When I am close I listen to a string bass recording to adjust and confirm.  I use Room Equalizer Wizard software and a MiniDSP UMIK-2 microphone.

Use yer earballs for setup...a test CD (I use one of the Stereophile CDs) helps but really that's all the technocrap needed unless, can't hear. Also, listening to music is always a good idea. I have 3 RELs bought used over the years and they're great...two for hifi and one for video (different rooms). 200 bucks of so each. One monster Mackie in my music studio also...that one goes down to 19hz and weighs a ton (Mackie HRS 120, no longer made but a way cool 92 lb. beauty). Subs add reality to the show as life (remember that?) is full of natural lowness (frequencies, not "low lifes" although those exist uncle Phil was which is why your main speakers will sound happier with subs. 

 ((((( @audioconnection    What is it about the design of the Vandersteens that allow them to behave so differently as a stereo pair with essentially the same control systems?))))

Its real simple every room is different and the Vandersteen Sub 3s adapt first by not having to play around with DSP processing that also spoils mid range. The Sub 3s feature their 11 analog adjustable pots for the left Channel and 11 for the Right channel achieving a far better in room response then other designs allowing the whole system to perform well in any room at its best!


Vandersteen Dealer NJ

[JohnnyR]  Its real simple every room is different and the Vandersteen Sub 3s adapt first by not having to play around with DSP processing that also spoils mid range. 

Vandersteen systems provide wonderful results.

Full system Digital Room Correction such as Anthem ARC, Trinnov or Dirac Live can affect the midrange and / or the entire frequency bandwidth. 

Digital Signal Processing subwoofers with onboard automatic processing such as JL Audio, SVS and Velodyne, to name a few, are limited in their high frequency to somewhere well below 200Hz. Even so, many experience an enhanced midrange using most subwoofers not spoiling it.  

Methods of subwoofer equalization / optimization, including the Vandersteen manual EQ vary greatly. Despite these differences its widely accepted in terms of system integration and ones desired low frequency presentation they far exceed those subwoofers equipped with only basic switched crossover and phase selection.