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Fostex FF 105 WK

Pair of Fostex FF-105 WK 4 inch Fullrange Drivers

Fostex new FF series has several improvements. New developed two-layer cone consists of long-fiber wooden pulp for the basic layer and short-fibred kenaf for the surface layer. The center cap has a special ridge dome shape. The cone paper, the spider and the voice coil were glued at one point for high-frequency response enhancement.

This is the manufacturer's brochure  Link To Fostex FF-105 WK Manufacturer's Datasheet

My Measurements

Driver Properties Thiele - Small Parameters
Chassis material Stamped Steel   Parameter Measured Datasheet
Membrane material Two Layer Paper Fs 79Hz 75 Hz
Magnet System Ferrite Re 6.7 Ω 6.7 Ω
Surround Cloth Qms 4.9 4.2
Voice Coil Diameter 20 mm Qes 0.49 0.46
Nominal Impedance 8 Ω Qts 0.45 0.41
Sensitivity 88 dB/W/m   Vas 3.9 ltr 4.85 ltr
Rated Power 10W Le 0.06 mH 0.041 mH

SPL Responce of Fostex FF-105 WK at 1m on axis and 15 30 deg off axis

Frequency response at 1m with 2.83 V input RED - on axis, BLUE - 15 º off axis, GREEN - 30 º off axis. Very good off axis performance. The peak at 7500 Hz is not annoying enough to be treated with crossover.

Second, Third and Fourth Harmonic of Fostex FF-105 WK in 18 ltr sealed box

The second, third and fourth harmonic curves measured at 2.83V input RMS.

Burst decay Responce of Fostex FF-105 WK at 1m in 18 ltr sealed box

Burst decay response, measured at 1m on axis

The impedance of Fostex FF-105 WK in 18 ltr seled box

The impedance curve in 18 ltr sealed box


This driver was designed for bassreflex applications. It can be successfully used in a Transmission Line or Onken constructions too.

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