SCA Penultimate

A 15” cone moves roughly three and a half times the air of an 8” cone at the same excursion. That difference is not subtle — it is audible, visceral, and present in a way that smaller full-range designs, however accomplished, cannot fully replicate. Bass from a 15” single driver is not an approximation; it is the direct output of a cone that has the surface area to reproduce low frequencies at full scale.

The SCA Penultimate is a bespoke, handmade loudspeaker built around a single 15” full-range ferrite driver. No tweeter. No crossover network. One driver, one voice coil, one unbroken signal path — and the spatial coherence that only a single-driver design delivers across the entire frequency range. Each pair is built to order in the Blue Mountains, NSW.

Sensitivity

At 96.7dB, the Penultimate is among the most efficient loudspeakers in the SCA range. A single watt produces output well in excess of normal listening levels. The rated input is 50W — but with this sensitivity, most listening sessions will draw single-digit watts at most. The result is that even a low-powered single-ended tube amplifier operates comfortably within the cleanest, most linear portion of its power curve.

Driver

The 15” ferrite driver uses a paper cone on a cast aluminium frame, with a fabric surround and Conex damper. An aluminium phase plug with gold centre cap replaces the conventional dust cap — distributing high-frequency output more evenly across the listening space and extending treble response toward 16kHz without a dedicated tweeter.

A copper shorting ring (Faraday ring) in the motor assembly reduces inductance variation across the voice coil’s range of motion. The practical effect is reduced intermodulation distortion and improved linearity at higher frequencies — a refinement that becomes particularly audible on a driver of this size, where the voice coil gap is substantially larger and the motor forces involved are correspondingly greater.

The driver’s 8Ω nominal impedance (Re 6.8Ω) and Qts of 0.322 are well-suited to bass reflex loading. The very low Fs of 31.7Hz — unusually low for a full-range driver — combined with the large Vas of 337L means the driver is designed to produce genuine bass extension in a suitably large enclosure. The 228L bass reflex cabinet provides exactly that.

Cabinet

Bass reflex enclosure. 228 litres displacement. The Penultimate is a large cabinet — designed to load a 15” driver correctly, not minimised for convenience. At 1100mm tall and 42kg assembled, it is a significant piece of furniture as much as audio equipment. The proportions are calibrated to the driver’s Vas, and the port tuning extends low-frequency output below Fs.

Tube amplifier compatibility

The Penultimate’s 96.7dB sensitivity and 8Ω impedance make it an exceptional match for single-ended tube amplifiers. At 1W input, output is already at a level that fills most listening rooms. At 2W, it is authoritative. The amplifier spends the entirety of most listening sessions operating at a fraction of its rated power — exactly the operating region where a single-ended triode design is at its cleanest.

Recommended amplifier power: 1W–50W. The Elekit TU-4523, running 45 or 2A3 output tubes at 1–2W, is more than sufficient. Other well-matched amplifiers in the SCA range include the Elekit TU-8400 and the Spotfire SE5.

Finish

The Penultimate is finished in genuine timber veneer (Woodgrain). Given the scale of the cabinet — 1100mm tall, 42kg — it will be present in the room in a way a smaller speaker is not. The finish reflects that.