Fostex FP 203
![Pair of Fostex FP-203 8 inch Fullrange Drivers](images/Fostex_FP_203_pair_view.jpg)
The Fostex FP series is unique with its large voice coil
diameter, in fact the largest one of all known eight-inch full-range
drivers . It looks a bit unusual with its distinctive whizzer cone
made of a special paper with thin carbon fibers. In Europe it was
branded ACR.
This is the manufacturer's datasheet
![Fostex FP-203 Label Early version](images/Fostex_FP_203_old_label.jpg)
The early production has rated power of 15W, whilst the later drivers were labeled 35W. In fact both versions are completely the same.
My Measurements
Driver Properties | Thiele - Small Parameters | ||||
---|---|---|---|---|---|
Chassis material | Vacuum-molded aluminum alloy | Parameter | Measured | Datasheet | |
Membrane material | Paper | Fs | 37.8Hz | 40 ± 8 Hz | |
Magnet System | Ferrite | Re | 7.4 Ω | N/A | |
Surround | Impregnated Cloth | Qms | 4.6 | N/A | |
Voice Coil Diameter | 42 mm | Qes | 0.22 | N/A | |
Nominal Impedance | 8 Ω | Qts | 0.21 | 0.30 | |
Sensitivity | 95 dB/W/m | Vas | 61 ltr | 40 ltr | |
Rated Power | 15/35W | Le | 0.24 mH | N/A |
This driver is suitable for back-loaded horn applications.
That's why I included a measurements in so-called "Universal" Horn.
More details about this project can be found
here.
![SPL Responce of Fostex FP-203 at 1m on axis and 15 30 deg off axis](images/Fostex_FP_203_15_30.png)
![SPL Responce of Fostex FP-203 at 1m on axis in the Universal Horn](images/Fostex_FP_203_UNI_0_15_30.png)
Frequency response at 1m with 2.83 V input RED - on axis, BLUE - 15 º off axis, GREEN - 30 º off axis
This driver has flattest membrane of all the speakers in the
measured BLH group and it is no surprise that it has the best off-axis
response.
![Second, Third and Fourth Harmonic of Fostex FP-203 in 18 ltr sealed box](images/Fostex_FP_203_THD.png)
![Second, Third and Fourth Harmonic of Fostex FP-203 in the Universal Horn](images/Fostex_FP_203_UNI_THD.png)
The second, third and fourth harmonic curves measured at 2.83V input RMS.
![Burst decay Responce of Fostex FP-203 at 1m in 19 ltr sealed box](images/Fostex_FP_203_BD.png)
![Burst decay Responce of Fostex FP-203 at 1m in the Universal Horn](images/Fostex_FP_203_UNI_BD.png)
Burst decay response, measured at 1m on axis
![The impedance of Fostex FP-203 in free air and in 18 ltr seled box](images/Fostex_FP_203_Z.png)
![The impedance of Fostex FP-203 in Universal Horn](images/Fostex_FP_203_UNI_Z.png)
The impedance curves
Conclusion
Fostex FP-203 is a driver for audiophiles, who love bright and in the same time non-intrusive midrange performance. Some audiophiles describe its sound as noble and delicate. It is suitable not only for back-loaded horns, but also for BVR and even bass-reflex constructions. It is a good idea to support FP-203 with a supertweeter like Fostex FT-96 or similar. This driver is well compatible with most of SE tube amplifiers.