Gentle reader,
As promised in the first part of this post: The Robb Collections: Installing the upgrade kit for Minimus 7 speakers Part 1 . I have received the woofers I bought via ebay that were once in Optimus Pro LX-4 speakers. They are made of woven Kevlar which is the main bullet-stopping material in bullet proof vests and also is used in military helmets. Stronger than steel, but much lighter.
As you can see, above, they are the same frame as the paper-coned Minimus 7 woofers. So, they are an exact fit. Kevlar looks so much cooler, doesn't it?
Each magnet seems to be the same size. They were made in different countries. The M-7 has a bump on the bottom for some reason only the designer knows. Note that the LX-4 models have a hole clean through the middle. This is to vent the inside of the center cap. Perhaps it also cools the voice coil.
The bump is more obvious from the angle below.
Below, you can see it installed in the Minimus 7W speaker.
Above and below is my idea and result to hold all four pairs of speakers on one bracket. In case you haven't seen my listening room before. I bought two brackets designed to hold a small, say 13" conventional (CRT) TV. They mount to wall studs and thus provide a steady solution for speakers. I bought them originally to hold my BOSE 301 speakers that my loving wife bought me years ago with hopes I would get rid of the large (15" woofers) speakers I was using. At the time, the stereo was in the living room.
The upper photo is the right bracket and above is the left. Note that all four speakers are in the same order on both shelves.
Oh, forgot to tell you, the original shelves are made of sheet steel, so they are not wide enough for more than two speakers. I acquired some 1/4" Lexan sheet which happened to be dark tinted. Lexan is a brand name of a poly-carbonate sheet that is often referred to as "bullet-proof-glass". Not when it's this thin, but it IS unbreakable.
Back to why I put both pairs in the same order. My thinking is that it keeps each pair the same distance apart. The room is too small to detect any shifting of the sound stage in either direction.
I secured the Lexan sheets to the steel shelf with Blu-Tak a form of putty that is sticky, but doesn't leave residue or parts of itself. I also used four pieces of it under each speaker as you can just see through the Lexan.
These shelves are adjustable in many planes. Originally made for hospital rooms or a small bedroom TV, perhaps.
So, how do these vintage Radio Shack Minimus 7 speakers sound now that I have put so much money and effort in to them? VERY good!
When I first tried them, stock, so to speak, I was unimpressed. I'd read about the ebay seller and his upgrade kit, so I decided to give it a try. I can't tell you exactly what difference the Kevlar woofers make, but rigid cones are what the better speaker makers seek, so Kevlar verses paper seems to accomplish that.
Good luck trying to get a pair of these woofers. Optimus Pro LX-4 speakers have a cult following for their amazingly clean sound. The have the front mount version of the top-mounted Linaeum tweeters on the Optimus Pro LX-5II speakers next to the M-7s.
In case you missed prior blogs, the left speakers are current model AR PS-215 speakers. They too have quite the following and have amazingly deep bass for 5" woofers.
Next is the Minimus 11 die-cast speakers I upgraded with Dayton Audio ribbon tweeters and woofers from Parts Express.
Next, the aforementioned LX-5IIs which I also used the same woofers in. THEY have the full 360 degree Linaeum tweeters atop them. All have their unique sound and all are keepers!
Thanks for looking!
Scott
