While working on an Econowave, I discovered the compression driver (Faital pro) had failed. Opening it up to investigate, I found the wire connecting the voice coil to the terminals had come loose. It was a simple quick repair job, but a little fiddly. In the process I had a look at the diaphragm and novel phase plug:
Here you can see the phase plug (orange). The centre hole does not let sound through. The radial slots around the outside allow the sound through.
Here you can see the diaphragm (lighter coloured part). The circumferential groove is the moving diaphragm, and you can see how the phase plug shown previously matches up. This unit was used in an Econowave.