The Seas H1212 is one of the most highly regarded tweeters amongst DIYers… for good reason. You can check out some of its measurements at Zaph Audio’s tweeter measurement pages, and you can check out the manufacturer data at Madisound’s site. One of the things that everybody has an opinion on is the hexagrid cover. Some will not buy a tweeter without it (these are usually people with kids 
) but many find it ugly. Still others talk about the negative effects of the phase shield attached to the inside of the grid cover. I decided to see what happens when you take the thing off.
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.
Hi and thanks for the great post. What do you make of the droop from 5 to 8K in the graph without the phase grid? It would appear that this would be fairly audible.
@Armand
I think that dip is diffraction. The reason it does not fill in off-axis like the other diffraction effects is because the response is already falling off off-axis at the higher frequencies.
You might be right Chad as this tweeter usualy measures pretty flat in this range.
I’m going to try a comparison tonight. What positive differences did you hear without the plate? More detail I presume? You didn’t hear any premature roll-off off axis without the phase plate?
Thanks.
Armand
Hey, nice article, especially including distortion measurements.
However, to me this looks like a big difference! I guess that the FR plots are various degrees off axis, and at first glance they look pretty much the same. However the response without the grid droops off evenly from 5k if the light-brown line is 0 degrees (lowest line in FR without grid, and highest line in FR with). Its almost inverse of the FR with grid, as here the light-brown is almost flat. So it seems that without the grid you will have drooping on-axis response, while off-axis is flat? Might work well in a waveguide? Does the DXT tweeter have a phase-shield?