The SCA Seamless Sub extends the low-frequency performance of full range and open-baffle loudspeakers without disturbing what makes them special. Upward-firing, sealed, and powered by a 250W plate amplifier with a 4th order variable crossover, it adds true low-end foundation — tuneable to the room — while the speed and transparency of the main driver remains intact.
The plate amplifier
The 250W plate amplifier delivers 156W RMS into 8Ω (0.1% THD) and 252W RMS into 4Ω. A variable low-pass crossover spans 40–180Hz at a slope of 24dB per octave (4th order), allowing precise frequency matching to any main speaker. A switchable +6dB bass boost at 35Hz adds low-end weight for smaller rooms or recordings that call for it. Variable gain, 0°/180° phase adjustment, and a 90dB signal-to-noise ratio (A-weighted) complete the integration controls.
An auto-on circuit activates the amplifier the moment a signal is detected and returns it to standby after 10–15 minutes of silence — no separate power management required. Soft-clip circuitry provides clean output at high programme levels and protects the driver from overload.
The amplifier accepts both high-level inputs (speaker binding posts) and low-level inputs (RCA). When connected via the high-level inputs, a built-in 6dB/octave 125Hz high-pass filter is applied to the main speaker outputs, providing a degree of bass load relief for the main amplifier.
The driver
The Seamless Sub is built around the Peerless by Tymphany SLS-P830667 — an 8-inch, 8Ω driver from the SLS line, specified for subwoofer and bass-reinforcement applications. A coated paper cone, rigid steel basket, ferrite magnet motor and aluminium shorting ring combine low moving mass with controlled distortion performance. The paper cone’s speed and light weight are the reason the Seamless Sub integrates convincingly with fast, high-resolution main speakers rather than muddying them.
The driver has a resonant frequency (Fs) of 42.19Hz and a maximum linear excursion (Xmax) of 8.4mm, producing the depth and authority the format demands without overhang or bloom. Sensitivity is 86.67dB @ 2.83V/1m. Rated to 90W input. Available in black or white to suit your installation.
Room integration
Gain, crossover frequency and phase controls allow the Seamless Sub to be adjusted for the room and the main speakers independently. As a starting point, set the crossover to 60–80Hz for full range speakers with good bass extension, and use the phase switch to find the setting that produces the most seamless transition at the listening position.
A pair of Seamless Subs connected via low-level (RCA) inputs can be individually driven — one per channel — for improved stereo bass imaging and precise left/right level matching.
Whether your preference is John Bonham in full flight, jazz double bass or full orchestral, the SCA Seamless Sub delivers a serious lift in overall system performance — the kind that is felt before it is noticed.
Specifications
| Plate amplifier power | 156W RMS / 8Ω (0.1% THD) • 252W RMS / 4Ω (<1% THD) |
| Signal-to-noise ratio | 90dB A-weighted |
| Low-pass crossover | 40–180Hz variable, 24dB/octave (4th order) |
| Bass boost | Switchable +6dB @ 35Hz |
| Phase adjustment | 0° / 180° |
| Inputs | High-level (binding posts) + low-level (RCA L/R) |
| Auto-on | Signal-activated; standby after 10–15 min |
| Driver | Peerless by Tymphany SLS-P830667, 8-inch, 8Ω |
| Resonant frequency (Fs) | 42.19Hz |
| Max linear excursion (Xmax) | 8.4mm |
| Sensitivity | 86.67dB @ 2.83V/1m |
| Driver finish | Black or white |
| Power requirements | 115/230VAC switchable, 400W |
Compatibility and cabling
The Seamless Sub is a recommended addition to any SCA loudspeaker system and integrates directly with the SCA tube amplifier range. It is equally suited to any system with a preamplifier output or speaker-level output.
The Elekit TU-8900 is a particularly well-matched partner. Equipped with twin pre-out jacks, the TU-8900 allows a pair of Seamless Subs to be connected via individual low-level RCA feeds — one per channel — without splitting or adapting the signal. Each subwoofer receives a dedicated channel, preserving left/right separation at low frequencies and delivering bass imaging that reinforces rather than diffuses the stereo presentation of the main speakers.
Cabling can be prepared to your length specifications — see SCA_SS_CABLE/1.