Sehring's S903 isn't just a multi kulti on chambers but settings, too. Here I'm not even referring to the alternate resistors which a dealer can easily roll into the filter to accommodate particularly challenging acoustics or special tastes. I'm talking of three toggle switches plus a non-stepped potentiometer on the speaker's back. Clicks above 10kHz—one or two dB up from neutral—address the super treble's airiness or subliminal freshness. The middle toggle affects the 300–3'100Hz band between the 2nd-order hi/lo pass filters of our short 3-way and again offers the same stops. The third toggle addresses +300Hz damping. This influences transient steepness to either tune for crisper cooler freshness or rounder warmth. Particularly during the break-in period, I experimented extensively with these tuning options. The S903 starts off quite bassy which mostly normalizes with use. After about 200 hours of action, I thus preferred all switches at their neutral position.

Below the toggles we find a rotating control log-scaled from 1-100 for visualization help, not to represent actual values. What do we massage here? Let's back track. The lowest driver is a passive radiator, thus without a motor or connection to the xover. That replaces a standard bass-reflex port. This 22cm membrane is passively driven by the active woofer through the mechanical spring action of a shared air volume. It eliminates port chuff and undesirable midrange contributions over common bass reflex vents. Enter the paralleled pot. It behaves like a load generator for the passive radiator. Position '0' equals a short circuit for maximal load, '100' represents 50Ω, above '100' to full stop means an open switch for limitless resistance aka minimum loading.

Theory turns sonic sense when you envision how higher values here mean easier membrane motion. That equals higher output and more extension/pressure particularly -50Hz. Sehring only advocate settings below 100 for close-boundary placement. In my less bass-critical room about 1 meter from the wall, I found '70' best but that's also relative to personal taste. Yet that still wasn't the end of playing doctor in the audiophile sandbox. One can even unscrew the center plug of the passive radiator to access stacked metal discs beneath. By removing some, one alters its moving mass, hence resonant frequency. The end points are 21Hz and 27Hz. Lighter means less extension but more power higher up. The upshot is obvious. Keep your twitchy fingers clenched and live with things as they are. Only on a rainy Sunday afternoon many moons later, perhaps with a good cuppa, think about the final tuning. But even then don't change more than two discs per session.

Time for an intermediate assessment? No matter what, a Sehring is a Sehring is a Sehring. We'll get to details in a moment. For now, I'll already say that these passive radiators are as unusual as they are massively practical. The toggle switches respond to personal bias or a particular amplifier to possibly decommission future hardware swaps. But the adaptive bass loading effectively counters side effects from enforced speaker positioning or room acoustic issues. And that solves actual problems rather than caters to preferences to be worth an early round of applause!