Improving Radio Shacks vaunted Optimus Pro (Linaeum ribbon tweeter) LX5II speakers with Dayton Audio woofers.

Gentle reader,

You may recall my finding old Radio Shack Minimus 11 die-cast aluminum stereo speakers:

The Robb Collections: NOW finished: Upgrading old diecast Realistic Minimus 11 speakers Part 2.5

Well, you may also have seen that I scored a pair of Radio Shacks vaunted Optimus Pro LX5II speakers with Linaeum ribbon tweeter for only $25.00 via ebay.

Like so many older speakers with foam surrounds (the ring of material that attaches the front edge of the woofer cone to the metal framework that is screwed to the cabinet baffle) had started to tear. BTW, "baffle" is what the front panel of a speaker cabinet is called.

While testing the SONY six-channel preamp (that is now on it's way to the next steward) I heard a buzzing sound in the left channel and blamed the SONY. Only later did I see that the foam had torn on that speaker. Oops.

Some years ago, I came up with the idea of a preventative step that would hopefully stop any future failure of foam surrounds in this post: The Robb Collections: Rubberize your woofers!  I plan to coat the famous red foam surrounds on my Cerwin Vega speakers next to save them from failure.

So, I thought, "I have left over speaker glue, it should repair the tear and then I can coat both sides with RTV* and that should fix it." Well, I did so and when applying the RTV Silicone glue to the inside of the foam, it tore through at the same spot. 

*Room Temperature Vulcanizing Silicone rubber glue. Great stuff, but it puts out nasty fumes so use it with a small fan blowing away the fumes, or outside. BTW, no matter what the actual temperature is, it IS room temperature. I learned that from "Real Facts" inside of a Snapple bottle cap.

Now, there are lots of people that will gladly sell you new foam for your old speakers. I have had mixed results with this process, so did not want to go that route. Remembering how great the Dayton Audio five inch woofers sound in the Minimus 11 speakers (link above and shown below, as well as a link to Parts Express' page) so did some measurements and decided they would work.

Above is one of the completed speakers with the new Dayton Audio Designer series five inches (5") woofers which have rubber surrounds. Here is a link to their page for these woofers:
Dayton Audio DS135-8 5" Designer Series Woofer Speaker  

Now, below is a picture of the original woofer installed in the cabinet:

See the difference? The fact that the surround is made of foam is obvious. Foam is much cheaper than rubber but over time it degrades. 

Next is photos showing the process of replacement. As you can see, the woofer is installed from the rear, but how to get to it? I had to figure out how to open these cabinets. Unlike the Minimus 11s, these have a molded plastic front piece for the baffle. I looked on line for and found images that showed me how: Pry out the rubber plugs on the front that conceal the four philip's screws. Careful prying after removing the screws and the front baffles came off easily. 

Here is what's inside:

Note how the designer used different kinds of material to direct or absorb the rear sound waves from the woofer. I have left it as is with the new woofers. Later, I may try adding more polyfil material.

I have heard of, but had never seen a crossover that uses a light bulb as a resistor. But here is one. The yellow device is a non-polarized capacitor used to stop all music below a predetermined frequency from reaching the tweeter. The round item is a coil that does the opposite; block all music above a predetermined frequency from reaching the woofer. That's what crossovers do.

The Dayton Audio woofers have both terminals the same size. They are 1/4" so I bought a bag of 1/4" and a bag of 1/8" terminals via ebay for this and future speaker projects. Cut off the old ones, strip the wires and crimp on the new terminals. Just remember, red is positive. Polarity is important.

Above and below is the new woofer in place. I know it is not centered. I repeatedly got it centered and when tightening the screws, it always moved. The OCD part of me hates that, but the rational part overruled and it accepts that it doesn't affect the sound.

I used an electric die grinder to turn the mounting holes on the woofer to notches. I did not measure the screw spacing, the woofers may have fit fine without doing that, but I didn't think of it at the time. The flat washers help hold it securely. 

As you can see, these woofers have huge magnets.

Now for some pictures of the old woofers which have steel shields over their magnets so that these speakers could have been used near a traditional television set. Modern flat screen TVs are not affected by speaker magnets.

Above is my attempt to rubberize the foam, but it failed. The tear can be seen at about the one o'clock area above. Note that below these are marked as 6 Ohm resistance. That has become the middle ground between the traditional four and eight Ohm choices. I do not know whether that makes a significant difference in the speakers performance with the new 8 Ohm woofers.

Below is the steel shielding cup over the magnet assembly. Note also that they have custom made mounting frame, unique to these speakers which came out in 1999 and sold for $149.99 a piece. That was a princely sum for small speakers, especially ones from Radio Shack. That's about $214.00 in today's money. Ever hear or see the word "bespoke"? That's British for custom made.

Now, for some comparison photos of the completed Radio Shack Optimus Pro LX5II speakers as well as the Minimus 11 units and the AR PS-215 which have traditional tweeters but also sport five inch woofers.

Note how much smaller these cabinets are than the other two. More in line with the Minumus 7s that have four inch woofers and came with either a small bass reflex port on the back or were sealed cabinets. The also sold with the Optimus Pro brand and as RCA models sold via Radio Shack.

You may be wondering what that convoluted foam is doing in the corners? Room boundaries can trap some frequencies or increase bass. I use the foam to prevent the former with speakers like my Cerwin Vegas that have rear bass reflex ports. 

And now some close up of the three different models.

I have yet to reinstall the rubber plugs that also hold the front grilles in place. LX5II is above, Minimus 11 below. Both have die cast aluminum housings. The Minimus' rear panel is steel and removable. Both now sport the same Dayton Audio woofers.

Below, the AR models (PS 215) which I believe are still being made. They also have had rave reviews as to their sound. And I agree, they sound really good.

A note on the trees. Back in the late 20th Century, I got interested in bonsai trees and had a number of them that I was tending to. They all died eventually. However, one can buy realistic looking ones such as these and they never need anything except the occasional dust removal.

Oh, yes, and how do the newly overhauled speakers sound? FANTASTIC! I put some classic rock CDs in the Nakamichi player and sat back. WOW! Do they sound great!

So, if you have or have always wanted to have a pair of these legendary speakers and the foam is bad, try what I did. You won't be disappointed.

Thanks for looking,

Scott