Victory lap or lag? Perusing Daniel Lee's Ultrumax descriptions, he believes that his driver's new 200Hz reach simplifies system assembly because ordinary popular subwoofers can easily add the missing bass. Having experimented along these lines, I'd call them potential fault lines. Truly seamless integration in the frequency and time domains isn't quite so simple. For a linear-phase handover, one ideally wants to high-pass the mains in a mirror image of the sub's low pass. The higher the system's overall quality, the more the chances that a fixed analog filter will be superior to what's on a plate amp. Next comes typical latency from modern subwoofers which convert their analog input signal to digital, perform heavy DSP, then convert back to analog. With our dual 9" Dynaudio S18 below, that delay is a blessedly low 2.5ms. A just 86cm physical offset now locks in time-coincident arrival with the remaining frequencies. Other subs might have 9ms latency or more. That requires 3-or-more meters to compensate. It quickly gets impractical. Who can or wants to set up their sub three meters closer to the chair than the mains? Yet late-arriving bass is slow bass. It's not what critical listeners should accept.

Augmentation mode runs the mains unfiltered to sneak in the sub below. To come off seamlessly requires matching the mains' acoustic roll-off with the sub's roll-in. The latter's low-pass usually reflects a 4th-order Linkwitz-Riley filter expressed as a -6dB value. That should match the speaker's which is usually not published. It can often be estimated by multiplying a published -3dB figure x 0.7 for a ported speaker, x 0.6 for a sealed speaker. The latter then wants a 2nd-order subwoofer low-pass to reflect a sealed box's shallower roll-off. Then there's the question of the transition frequency. In the above system, it's fixed at 40Hz. The mains start to roll off at 100Hz and are -24dB at 20Hz. Now there's sufficient stereo bass to make the sub's entry and location entirely inaudible. Shift up to a 200Hz filter hinge and that changes.

"The name Ultrumax derives from maximization of ultra bandwidth for AMT drivers. Our economical U-series monitors and active bass boxes are mainly designed for AV purposes and aim at our domestic market. The M1/M1-ST monitors plus passive bass enclosures are the hifi-grade proposition for the global audiophile market. You'd make great sound combining the Ultrumax M1 and Sub-IIps.

"Unfortunately during these economically challenged times, we can only afford to ship you monitors and stand. The Sub-IIps enclosures are too expensive for 2-way shipping and export/import fees. Any active sub you might have on hand won't have problems with our Ultrumax M1/M1-ST monitor as long as its SPL are sufficient for the room and it can be taken to 190-200Hz preferably with a phase adjustment for fine-tuning.

"A pair of monitors and mono sub are sufficient to build a true hifi system. Any serious audiophile understands this. Why I designed a pair of active/passive Sub-II enclosures was mainly because floorstanders look better, better conform with the traditional image of a quality hifi system and lock in the same physical distance for the monitors and woofers. The Ultrumax M1 has a rather sophisticated 190Hz hi-pass filter to present your amp with an about 4-6Ω load which increases a lot below the filter."

Our Zu sub's highest low-pass value is 110Hz, that of the Dynaudio 120Hz. Both use standard 4th-order Linkwitz-Riley filters. Could the -6dB point of Daniel's satellites match theirs? If so, I'd be in biz to run with the assignment. If I couldn't sub high enough, I'd be out. Daniels' response made it so. "The -6dB point of Ultrumax-M1 is ~170Hz. Your subwoofers won't be suitable." I'd suspected as much. Now synchronicity intervened when Canadian contributor Glen who proudly calls a pair of Mark & Daniel Maximus MkII monitors his own reported that his SVS SB3000 sub has an upper low-pass limit of 200Hz. "To do a preliminary test, I disconnected the woofer feed on the Maximus monitor and ran the sub at the 200Hz filter with the AMT. Yes there was obviously a gap but I was quite shocked. My old huge Paradigm subwoofer could never be taken beyond ~60 cycles without showing character. The SVS stays clean to 200Hz. The damn thing is fast and clean. Even with the response gap, it kept pace with the AMT drivers so not only had subsonic weight but responsive woofer properties. Clever bunch, those SVS people." As such our Ultrumax review was back on by handing over to Glen. – Ed.

… to be continued…