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As you can see, the 3rd harmonic doesn’t change apreciably. The 2nd on the other hand increases dramatically with each doubling of the SPL.

The cover is not hard to remove, or replace for that matter. All you need to do is grab it with some small pliers and pull… that’s it. It is held on by some tacky glue and can be replaced with just the power of the magnet and the tackiness of the glue. The only thing to watch out for is the possibility of the cover being pulled into the delicate dome by the magnet, so just be careful and make sure you have a good grip. These measurements were taken on a poorly planned baffle and therefor include some serious diffraction effects.

Frequency Response with Grid

Frequency Response without Grid

As you can see, the phase shield effects the top octave dispersion pattern and not much else.  Personally I don’t see the reason for the shield from these plots, the response without the grid looks better to me, but I have heard it argued the other way too and obviously SEAS thinks it is better with the shield, or they wouldn’t have put it in there.

So does the phase shield effect any other aspects of the driver?  Here are some distortion plots with and without the shield:

Inter-modulation Distortion with Cover (30 degrees off axis)

Inter-modulation Distortion without Cover (30 degrees off axis)

Swept Distortion with Grid (on axis)

Swept Distortion without Grid (on axis)

Swept Distortion with Grid (30 degrees off axis)

Swept Distortion without Grid (30 degrees off axis)

So, what does it all mean?  It means I wasted a lot of time!  The only difference I can measure is the FR difference above 10k.  So leave it on?  Take it off?  I would take it off.  Testing with my ears is always part of the process too, and there is definitely an audible difference between the two.  I prefer the sound without the phase shield.  The good news is that it is the little sticker inside of the grid that acts as the shield, so if you want you can remove the sticker and keep the shield on.  The even better news is that since it really doesn’t change the frequency response below 10k you can do this with any of the available designs that use this popular tweeter and not have to worry about ruining the crossover.