RADIO SHACK 40-1271 SPEAKER
The Radio Shack 40-1271 is an 8" fullrange driver with a dual cone (whizzer). It features an accordian style surround and the cone is curvilinear. The frame is stamped steel and the motor (magnet) is rather small considering the size of the driver. Photograph 01 below shows a front view of the speaker.
Photograph 01: Radio Shack 40-1271 Full Range Driver - Front View
The specifications listed on the Radio Shack box of the driver are: Impedance 8 ohms, Magnet Weight 81 g, Freq. Response 75 - 20,000 Hz, Sensitivity (SPL) 88 dB, Power Handling (RMS) 5 W, Power Handling (MAX) 10 W, Cone Material Paper
Table 01 below shows an average of the driver parameters as measured from fellow DIY'ers. The driver data has been collected from the Fullrangedriver archives.
| Fs | 82.9 Hz |
| Vas | 1.16 cu. ft. |
| Qts | 2.43 |
| Qes | 3.3 |
| Qms | 9.45 |
| Re | 7.9 Ohms |
| Le | 2.1 mH |
| Mms | 7.5 grams |
| SPL | 89.5 dB |
Table 01: Average T/S Parameters - Radio Shack 40-1271
As you can see from the measured driver parameters, this driver will work best in an open baffle or aperiodic enclosure combined with a low frequency driver or subwoofer to fill in the bottom end. The ultra high Q causes a considerable peak in the frequency response between about 60 and 160 Hz. In an open baffle configuration, the 40-1271 driver needs a baffle width of about 34" in order to flatten the frequency response to about +/-3 dB up to 2 kHz. Above about 2 kHz, the driver begins to beam.
Driver Tweaks
The Radio Shack 40-1271 will need the usual cheap driver tweaks for best performance. Damping the basket, gluing the motor to the frame and the $0.98 whizzer tweak.
Photograph 02: Radio Shack 40-1271 Full Range Driver - Rear View
If you knock on the stamped steel frame, you hear that it rings, so it needs to be damped with ductseal. See the Radio Shack 40-1197 (FE103) for a good example of how to damp the driver frame using ductseal. The legs of the frame are wide, so stick some ductseal on the inside of the legs to reduce reflections back through the cone. Also, the motor is not attached very well to the frame, so fill the gap with ducseal or better yet with an epoxy.
The whizzer resonates at about 2 kHz and creates what many refer to as upper mid-frequency "shout". You can try listening to the speakers off axis (about 15 to 20 degrees) from your listening position. Also, there is Marc Wauters 98 cent whizzer tweak. This tweak consists of placing a lightweight piece of foam between the outer edge of the whizzer and the main cone. This tweak help reduce the resonance peak of the whizzer. Unfortunately, Marc has removed this tweak from his site.