Fostex FE-208
A full-range driver that asks you to give up the crossover, and pays you back for it.
Overview
The FE-208 is one of the drivers that built Fostex's reputation among single-driver purists. The appeal is simple. No crossover, no network losses, no phase weirdness at the crossover point. One driver, one signal path, and whatever the cone can do is what you hear.
What the cone can do depends largely on the motor. Fostex's published Thiele-Small data for the FE208X lists a free-air resonance of 45 Hz, a Qts of 0.21, and a Vas of 36.9 liters. Those numbers describe a fairly stiff, well-damped driver with a strong motor. The low Qts is the figure that counts most here. It means the driver wants a horn or a properly tuned vented enclosure, not a sealed box. In a closed cabinet you get lean, thin bass. Put it in a back-loaded horn or a quarter-wave pipe sized to that 36.9-liter Vas and 45 Hz Fs, and it reaches down with surprising authority for a driver with no woofer behind it. The 8-ohm nominal impedance suits tube amps and low-power solid-state alike, which is the crowd this driver was aimed at.
Sensitivity is the other headline. Fostex rated the FE208 Sigma at 96.5 dB, so it makes real volume from a handful of watts. Pair it with a 2A3 or 300B single-ended amp and it plays louder than the numbers on the amp's faceplate would suggest. The tradeoff comes with the format: a single 8-inch cone covering 45 Hz to 20 kHz will beam at the top end, and the extreme highs roll off in a way a dedicated tweeter would fix.
The driver was sold both as a bare component and as part of Fostex's kit and enclosure lineup. Madisound offered the Fostex Sigma Series of full-range transducers as ideal for purists who don't want a speaker encumbered by caps and coils (Audio-Express, August 2001, p.8). The split between a bare X-model driver and a finished Sigma pair shows how the line was sold: the X for DIY builders rolling their own cabinets, the Sigma as a more finished proposition. Either way, the FE-208 was never a plug-and-play speaker. It was a component for people who wanted to design the box themselves or buy a proven Fostex plan.
The spec sheets show where the driver sits in the Fostex lineup. The FE168 is the 6.5-inch sibling, with a 60 Hz Fs and 92 dB (FE168X) or 94 dB (FE168 Sigma) sensitivity. The FE208 is the bigger, lower-reaching option at 45 Hz and 96.5 dB. The FE108X sits below both at 4 inches and 80 Hz.
Specifications
The X-model data gives an Fs of 45 Hz, 8-ohm impedance, Qms 4.03, Qes 0.23, Qts 0.21, Vas 36.9 liters, and an Mmd of 12.0 grams. The Sigma sheet lists the same 45 Hz-20 kHz response and 8-ohm impedance, but quotes sensitivity at 96.5 dB, and gives a diameter of 20 cm with a 100-watt power rating. The sensitivity figures differ between the two sheets. It may reflect different measurement conditions or a real difference between the X and Sigma versions, but the source documents don't resolve it. Buyers comparing the two should treat the 96.5 dB figure as specific to the Sigma version, since the X-model sheet does not list a sensitivity value.
The 12-gram moving mass is light for an 8-inch driver, which is part of why the FE-208 sounds quick and articulate rather than sluggish. Combined with the low Qts, it points to a driver designed for horn loading, where the enclosure does the bass work and the cone stays controlled. The 100-watt power rating is generous for a full-range driver and reflects the sturdy voice coil and motor structure. A 96.5 dB driver doesn't need a big amp anyway.
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