The Hertz DCX 690.3 three way coaxial derives from the combination of a real woofer with a 60mm midrange and a Mylar dome tweeter. You get linearity, good off axis response and tonal accuracy which you can't normally have with a standard coaxial speaker.
Specs Hertz DiEci DCX-690:
Component: 3 way Coaxial
Size: woofer 6"x9" midrange 60mm tweeter 15mm supertweeter
2 x 180 watt max
2 x 90 watt RMS
Impedance: 4 ohm
Frequency Response Hz: 45-21k
Sensitivity: 93dB
Outer diameter: 165mm
Mounting hole diameter: 152mm
Magnet size: 80mm
Total depth: 88mm
Magnet: High density flux ferrite
Cone: Water repellent pressed paper