I've always loved vector games of the 80's, and spent many a coin on Asteroids and Battlezone back in the day. Plus, the vector graphics looked ahead of their time back then, so that only made these games seem much more appealing.
Anyway, over this past summer I had an opportunity to buy a vector cabinet locally, and jumped at the offer, considering the game was in such great condition.
Space Duel is an interesting two player cooperative take on traditional Asteroids. Plus its a color vector game! There was only one problem I noticed with the cab, and that was a color blooming issue in the lower left corner of the vector tube. Actually it was more than just color, the convergence of the tube was pulling in that corner, but he adjusted the picture to be smaller in the center of the screen so the vectors weren't as affected as the colors were. This defect helped me in negotiating the price on the cab, and in my mind I thought it was really just a degaussing issue.
After getting the cab home, and using an external degaussing ring, the color blooming was not going away. I open the cab and inspect around the tube to make sure there was proper shielding, and noticed the original speakers under the control panel, and above the monitor were swapped out for larger size cones, presumably to give it better bass response. Larger speakers also means larger magnets attached to the back of the speakers, which were upsetting the magnetic balance the cab was originally designed for.
Since these are not high end car audio speakers with protective shielding, I would with have to either replace the speakers with original spec, or try to shield them myself. I chose the latter since the four larger speakers makes this cab sound tremendous!
A quick googling led me to Andy Rondeau's Do-It-Yourself (DIY) Speaker Project. Although at the top of the article, he states this information is now outdated (as you can now buy expensive speaker shielding kits), I liked his DIY approach with cheap Home Depot supplies.
So I measured my speaker drivers, and went to Home Depot to look for those same steel pipe cap/ covers (which were about $5 a piece). I also found some electrical boxes (for $1.50 a piece) with much thicker steel and approximately the same size, which fit quite snugly inside the cap covers.
I decided to return the more expensive cap covers, and just stick with the cheap electrical boxes as combined they didn't seem to add any additional shielding from my testing. The boxes were a bit larger than the two speaker drivers behind the marquee, but fit perfectly over the speakers under the control panel.
I used electrical tape to ensure the boxes didn't fall off, and to insulate the edge next to the speaker terminals. The results were amazing!