Meanwhile with 'normal' speakers, "I've experimented more on the path to subwoofer enlightenment. My current setup includes a pair of Nenuphar 10" monitors with one Cube Audio 12" sub positioned centrally facing me. Pál’s outstanding icOn 4SE takes care of preamp/xover duties. Your observations ring true. The biggest impact of the sub and filtering is the liberation of the monitors and their amps from the burden of low frequencies. This translates into a bigger soundstage, clearer transients and fuller/more articulated bass compared to the already very good Nenuphar 10" widebanders." That was reader Vincenzo Picone paralleling my experiments with different hardware.

"In which way might adding a second 12" sub improve things? My room is 5x6x3m WxDxH. Is it necessary to position the sub at the same distance as the monitors (sub is currently 1m behind)?" Though I'd not experimented with twin subs yet to have personal experience, the popular argument for them is twice the output hence lower excursion-based distortion. It's also said that placing subs in different locations loads the room more evenly. Arendal however advocate stacked corner placement to eliminate the two corner walls as late reflective boundaries; to make room interaction more predictable for easier EQ: and to generate line-source dispersion advantages. For music not movie purposes and using the same low 40Hz/4th-order transition I'm relying on, I didn't think Vincenzo would gain much if anything from going dual. It's with far higher transitions that the loss of stereo cues will become noticeable. As to how time alignment relies on path-length equality—additionally compensating for DSP latency where necessary—we already covered.

With the filter installed, Vincenzo's "bigger clearer" reaction syndicated in Westport for a rerun. But there was more. Particularly upper-bass dynamics gained snap and crack. And because I no longer set relative bass volume to wide-open mains which meant favoring more linear mid/upper-bass over low bass, I now had superior weight in the really low frequencies without suffering thickness in the next octave. Comparing sub solos between Dynaudio's and Pál's low-pass filters—same hinge, same slope, main amp muted—showed clearly less bleed into the 80-160Hz octave for the fixed filter. I don't know why or how but its attenuation action seemed sharper and more specific. The obvious price to pay is no more variability. But if you know your ideal filter value, going the superior fixed route seems a no-brainer.

Blessed relief.
• Cosmetic relief from compact monitors for a reduced visual footprint.
• Localization relief from a monitor's typical disappearance act.
• Acoustic relief from a fixed bass balance that can't be adapted to room, taste and occasion.
• Active relief from the lesser control of passive bass and its far less task-specific transducers.
• Relief from dynamic compression in the higher registers.
• Relief from bandwidth limitations.
• Financial relief from chasing similar bandwidth with passive towers where each 5 cycles gained could double expenditure.

In very unpopular 6moons fashion, that's seven good reasons for splitting the stereo job into sub/sat feeds, picking compact mains good to ~40Hz and doing active precision filtering of all participants. Feel free to disagree; but only if you've tried this. Wielding mere beliefs is just being argumentative without backing it up by actual experience. Without experience, you can't know the difference. That happens to be far from minor. If I were allowed just one word to describe it, I'd again choose visceral. With a properly integrated quality subwoofer which is appropriate for the desired SPL relative to room size, our music gains in gumption, groundedness, scale, venue cues, vitality and perceived realism.

Not half bad for a €1'390 addition considering how all other kit here is rather pricier. Thank you Dynaudio. Your 18S is making a sub.stantial difference to my upstairs installation. Add one happy punter to your feedback pages.

Postscript. Within an hour of publication, Greg Pasche wrote that "very interesting to read your various reviews on sub integration and ideal crossovers. I see that you tried the 18S augmenting the Vox with low pass set at 40Hz while waiting on your external filter. You said it would do in the meantime. Seeing as you did not mention it, I guess you did not try the 80Hz high pass i.e. taking the signal through the 18S using the variable low pass for sub 80Hz bass and taking over 80Hz line out to the Vox? On the off chance that you did try, is this significantly lower quality than augmentation? It is obviously a waste of the Vox's low bass capabilities but I was just wondering if for slightly lesser speakers this could be an interesting option?"

Greg is correct about this option and exiting line-out 80Hz would also bring Dynaudio's time-delay function into the loop whereby the mains can be delayed in DSP. But running my analog signal through additional A/D⇒DSP⇒D/A never appealed and indeed would waste Vox's force-cancelling woofers by driving up the handover frequency by a whole octave. In a different context, I do think it could be an interesting option and Dynaudio certainly think so themselves.

Postscript II. Half an hour later, Preston Lloyd wondered that "how you just wrapped up your new subwoofer review, I'm left to think that considering its price, you might just rate this as the most cost-effective upgrade you could have made considering your current system. Would that be a correct assumption by any chance?" I answered "very much so, Preston. Going out for a spot of sub proved to be the poshest dining experience I could have had now on a relative 'hamburger' budget. The proviso you rightly stated was the status of the system. With everything else sorted, nothing else would have given anywhere near this return for like coin. And in hindsight, that's really the point. If one planned a system from the get around a pair of good but certainly not über monitors to eye a ~40/50-ish -3dB point then added a Dynaudio-type sub, one would make guaranteed better sound from a rather less intrusive setup than going after really posh big passive tower speakers; and save nicely to boot."