Help with choosing sub-woofers please

@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?

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?

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.

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.

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 whathifi.com/reviews/kef-kc62 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.

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.