Fostex FF85WK Fullrange Speaker Driver Transducer
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Fostex FF85WK Fullrange Speaker Driver Transducer
The new Fostex FF85WK speaker drivers replace the Fostex FF85K driver. The Fostex FF85WK is a 80 mm diameter fullrange speaker driver. The FF85WK fullrange speaker drive unit employ a "double-layer" paper cone, rigid aluminum dust-cap and a pocket neck damper for high-quality sound reproduction. The 65 mm diameter ferrite magnet weighs almost 190 grams. The FF85WK can be used in a wide variety of enclosures specifically bass reflex and sealed enclosures and also with open baffle speaker systems. The Fostex FF85WK full-range speaker driver is capable of an extended frequency response that can cover from about 130Hz to 20kHz+.
Photograph 1: Fostex FF85WK Fullrange Speaker Driver
The Fostex FF85WK speaker drivers came neatly packaged in a cardboard box which indicated the speakers were manufactured in China. Inside the box is a foam gasket, four wood screws with washers and a datasheet with the driver specifications and speaker enclosure plans.
Photograph 2: Fostex FF85WK Fullrange Speaker Driver Box Contents
The Fostex FF85WK drivers are built on a stamped steel frame chassis. The lightweight stamped steel frame can "ring" and efforts made to "damp" and deaden the frame will improve performance from this little inexpensive driver. There are a number of possible modifications and tweaks that can be applied to this driver and some of them are shown on the modifications and tweaks page for small inexpensive fullrange speaker drivers.
The Fostex FF85WK drivers has a smooth and well extended response. I prefer the high frequency response of the Fostex FF--WK series of drivers over that of the FE-xxEn drivers which can impart their own coloration to the sound. This improved high frequency response seems to be the result of the aluminum dust cap for the FF--WK speakers. The Fostex FF85WK speakers are relatively inexpensive and have a high performance to price ratio.
Thiele/Small (T/S) Parameters - Fostex FF85WK Speaker Driver
The Thiele/Small Parameters of the Fostex FF85WK speaker drivers have been measured using the Dayton Audio Test Systems (DATS). The T/S parameters from the small signal speaker testing as well as the parameters noted on the FF85WK datasheet are summarized in Table 1. The measurements were made at about 18 degrees Celsius.
Table 1: Thiele/Small (T/S) Parameters - Fostex FF85WK Fullrange Driver
| Parameter | Fostex | Driver 1 | Driver 2 |
| Fs | 115 Hz | 135.9 Hz | 136.6 Hz |
| Vas | 1.036 L | 0.959 L | 0.963 L |
| Qts | 0.55 | 0.65 | 0.66 |
| Qes | 0.683 | 0.816 | 0.831 |
| Qms | 3.29 | 3.28 | 3.32 |
| Re | 7.2 Ohms | 7.13 Ohms | 7.17 Ohms |
| Le | 0.032 mH | -- | -- |
| Le @ 1 kHz | -- | 0.458 mH | 0.454 mH |
| Le @ 10kHz | -- | 0.237 mH | 0.236 mH |
| SPL | 86.5 dB | 86.6 dB | 86.6 dB |
Notes:
- SPL estimated with Radio Shack 33-2050 SPL Meter.
- T/S parameter measurements made with Dayton Audio Test Systems (DATS).
Figure 1 shows the impedance sweep of the Fostex FF85WK speaker driver produced using the Dayton Audio Test Systems (DATS).
Figure 1: Fostex FF85WK Speaker Measured Impedance
The frequency and impedance response plot from the Fostex FF85WK datasheet is show in Figure 2.
Figure 2: Fostex FF85WK Frequency Response and Impedance (from Datasheet)
Datasheet - Fostex FF85WK Fullrange Speaker Driver
- Fostex FF85WK Datasheet - (PDF 1MB)
Fostex FF85WK Recommended Bass Reflex Type Enclosure
Figure 3 below shows the Fostex Recommended Standard Bass Reflex Type Enclosure for the FF85WK speaker driver. This speaker box plan is from the Fostex FF85WK driver datasheet.
