Pioneer PIM-8L
Pioneer PIM-8L/PIM20A is a product of Fukuin Electric Ltd and can also be found under brands Hamlins and Lafayette. This driver is in production from the late fifties. Some audiophiles call this driver "The poor-mans Altec 755A" or even "The Japanese answer to 755A". However the construction of the PIM-8L and its performance are completely different from 755A. Actually PIM8L is a dual cone driver. The upper frequency range cone has firmly connection to the voice coil in its center and flexible connection to the LF cone at its periphery. That's why the manufacturer called the construction "Mechanical 2-way". The LF cone was perforated at the back as a way to avoid sealing an air volume between two membranes. The surround is a part of the cone and it has a lubrication, that seems to be hardened by ages. That's why the resonance frequency is higher than specified by manufacturer.
This is the only manufacturer's brochure that include PIM-8L
I found.
This a manufacturer's SPL graphics of PIM-20A
My Measurements
| Driver Properties | Thiele - Small Parameters | ||||
|---|---|---|---|---|---|
| Chassis material | Stamped Steel | Parameter | Measured | Datasheet | |
| Membrane material | Paper | Fs | 87Hz | 55-70Hz | |
| Magnet System | AlNiCo | Re | 12.4 Ω | N/A | |
| Surround | Impregnated Paper | Qms | 8.4 | N/A | |
| Voice Coil Diameter | 29 mm | Qes | 0.86 | N/A | |
| Nominal Impedance | 8 Ω/16Ω | Qts | 0.78 | N/A | |
| Sensitivity | 94 dB/W/m | Vas | 17 ltr | N/A | |
| Rated Power | 6W | Le | 0.61 mH | N/A | |
Frequency response at 1m with 2.83 V input RED - on axis, BLUE - 15 º off axis, GREEN - 30 º off axis.
The second, third and fourth harmonic curves measured at 2.83V input RMS.
Burst decay response, measured at 1m on axis
The impedance curve in 18 ltr sealed box
Conclusion
Maybe due to its age this driver needs support in the lower frequency. It has clear and detailed middles and a notable lack of trebles. The best application to my opinion is as a wide midrange in high-efficiency multy-way system.
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