Subbing out. Immediate pleasant surprises were zero hum on the woofers, zero mechanical buzz through the cab. I was fully prepped to intercede with a DC blocker. That's what the early Hypex plate amp on our big Zu needs to behave. The Dynaudio could plug straight into the wall with the provided power cord—the Danes actually include three to cover UK, US and EU plugs—and just sat there like a church mouse: in perfect stealth mode but ready to hustle. At my SPL, even the enclosure itself was shockingly passive. Given the compact cubic volume and internal pressure, one expects some resonant fallout despite force-cancelling drivers. Yet hands on during ambient synth bass workouts, the vinyl-wrapped black box with the satin beveled end caps betrayed precious little vibratory action. I was impressed.

Once my relative bass volume was right, I muted the main amp for some sub solos. A 4th-order 40Hz low pass hits -24dB@100Hz. Naturally there was faint bleed beyond. This is no brick-wall filter. Important was no impact debris. When dry bass beats struck like projectiles, they pounded dirt without causing raining spray that would take time to settle. This showed nice woofer control. Bass textures didn't linger. They stopped where they should. With the main amp un-muted, I had the expected one-piece blend. Nowhere did it betray the sub's location despite looking straight at me from not far away. I simply had a bit more 2nd than 1st octave weight. In full filter mode with mirror-imaged mains, that would equalize perfectly. When really low bass occurred which I knew was beyond the monitors' reach, I naturally heard a good subwoofer in the mix. Paying close attention to bass timing, I perceived no high-level blur from behind-the-beat bass, just normal room reflections lower in level. To minimize those would require a RiPol sub with lateral self cancellation or serious room treatments. In short, I was perfectly happy with my purchase already. I only looked forward to Pál's filter escaping the Brexitan customs misery of early 2021 to land on our Irish west coast a week later and finalize this installation. It's lovely whenever papery specs and associated propaganda overlay personal expectations to a 't'; especially since I'd inquired about latency only after the fact. That's a vital spec. Most makers of DSP subwoofers simply don't publish it because it's not exactly a point of pride. If you buy one, make sure to ask. You should want to know before you commit. If you don't, the notion of slow bass—which really is bass that arrives late—needn't be a myth. It could be very real.

UI. When the 18S first powered up, its display just went bright blue. It showed no commands. After powering down and unplugging the mains cord for a reboot, an error message showed in an unknown language. I persisted. Eventually a boot loader appeared with the numbered firmware version. Now the initial weirdness disappeared and everything worked. After your last input command, the display soon dims. Then it re-awakens whenever you prompt the push/turn control. Once all other values set as desired, you'll probably only use the control to fine-tune volume. That's in the top menu layer. It remains immediately accessible. Otherwise the only control you'll operate is the power mains; unless you set the 18S to timed auto on/off. I prefer not to accelerate circuit aging by leaving stuff permanently on. I turn off the sub from its switched UK wall outlet without any burps. Truly, the 18S is a well-engineered pert package for a very fair price. Because it's small enough to sit well out in the room, it works where the Zu Submission wouldn't have; and better at that. For my purely musical purposes, I noticed no sacrifices in extension or power. If anything, the Dynaudio goes lower. Again, it ticks off all my boxes. Why pursue a monster sub when this compact does the same job? Indeed.

On HifiStay Gyrotension isolators.

Why pursue filtering the mains with a precision high-pass filter? Because not doing so doesn't do the same job. It just doesn't. We'll get there next. First, the numbers again. Our ported monitors are -3dB/36Hz. That makes their -6dB figure ~25.2Hz. The lowest on can set the 18S is 40Hz. For that, the monitors would want to be -3dB/57Hz. Anything lower than that begins to cause unwanted overlap. That doesn't yet factor that stitching together mains run wide open with a sub won't guarantee a phase-consistent patch. Nor does it remove any stress from the mains' mid/woofers or woofers. Just bolting on a sub can't improve their dynamic range. That's at least two if not three calls against augmentation mode to favor dual filter mode – if said filter is of high quality to not compromise 90% of our bandwidth. For a truly invisible/seamless patch, dual filter mode is a guarantee, augmentation mode a less likely possibility. For dynamic gains above the sub's bandwidth, dual filter mode is a prerequisite. That's for when the main speakers lack their own beastly woofers. A costly 4-way or 5-way could already operate well beyond any untapped dynamic headroom. Now the equation changed. It's simply unlikely its owner would or should consider a subwoofer in the first place. Really, the equation goes away entirely. Stating that just keeps us honest to avoid blanket claims.