No-seam seamstress?

spl Audio's Crossover is for users whose subwoofer either includes no low-pass filter because it's passive; or who wish to bypass what's built in for something superior. It's also for those who prefer full filtering to include their main speakers. Now their voice coils no longer heat up from attempting bass they can't do, thus don't drive up their impedance to choke dynamic range higher up. It's why there's a matching high pass which can be set for 12dB/octactve (sealed mains) and 24dB/octave (ported mains). spl's entire circuit is analogue to involve no redundant A/D/A conversion.

Because spl cross over to hifi from pro, their outputs are on XLR. You'll need matching balanced gear or adapters. The firm's trademark are their Voltair discrete operational amplifiers. They run on ±60V rails so far higher than the industry-standard ±15V. That's done for expanded dynamic range and lower distortion. It naturally relies on quality parts fit for such higher purpose. Below we see the linear power supply with toroidal mu-metal shielded mains transformer; 2 x 4'700µF Epcos capacitors to stabilize the DC voltages; orange relays which are 18-carat gold plated and gas encapsuled; and, in the left photo, vertically installed Supra balancing and Supra operational amplifier cards plus an RK27 'Big Blue' Alps potentiometer for the subwoofer's relative volume.

In the upper right photo, we see the now installed top board. It splits into the low-pass filter with Panasonic PAM Gold series caps on its left, the high-pass filter with Styroflex capacitors on the right. Both filters use precision metal-film resistors and one each blue custom filter-frequency switch. The next photo shows a few of the 120V Voltair cards of which this half-sized component runs 21 total.

For the listener who insists on high-quality external filtering in the analog domain, options are scare. Bryston and Pass no longer make their subwoofer crossovers. According to my canvassing of the web, we're squarely down to JL Audio's, Wilson Audio's, M2Tech's… and spl's. None of them offer remote control. All are priced  at ~3K and up. Only today's comes in black, silver and red.

For the right kind of user, this could be the ace they were waiting on to finally win their game of perfect mains/sub integration?