Mark Audio CHS 70A
The CHS-70 is another fullrange driver from Mark Audio - a manufacturer, well known to many DIY-ers. It is mechanically similar to the CHR-70 series drivers, but its major design features are more advanced chassis construction, improved suspension and new shape of the dust cap.
This is the manufacturer's brochure for the nearest CHR-70A model
My Measurements
| Driver Properties | Thiele - Small Parameters | ||||
|---|---|---|---|---|---|
| Chassis material | Glass fiber injected plastic | Parameter | Measured | Datasheet | |
| Membrane material | Aluminum Alloy | Fs | 70.5Hz | 67.9Hz | |
| Magnet System | Ferrite | Re | 7.0 Ω | 7.2 Ω | |
| Surround | Rubber | Qms | 2.07 | 2.40 | |
| Voice Coil Diameter | 20 mm | Qes | 0.65 | 0.69 | |
| Nominal Impedance | 8 Ω | Qts | 0.50 | 0.54 | |
| Sensitivity | 85.4 dB/W/m | Vas | 4.7 ltr | 5.5 ltr | |
| Rated Power | 20W | Le | 0.05 mH | 0.035 mH | |
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.
There a noticeable peak of distortion at about 1500Hz.
We can see corresponding impedance and phase bumps at the graphics
below.
Burst decay response, measured at 1m on axis
The impedance curve in 18 ltr sealed box
Conclusion
The CHS-70 sounds really smooth, with very good micro dynamics and without a trend for irritating overtones, some metallic-cone drivers have. This fullrange speaker will perform well with a properly designed open baffle or a compact TWQT construction.
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