RTA 12 to 12B Conversion and Refurb
I picked up a pair of RTA 12's for a fair price on Craigslist a few months ago. I liked them, but heard that the 12B's sounded even nicer, so I picked up a pair of 12B crossovers, rewired the speakers, and yes, they certainly sounded better. Then I started reading about tweaks and mods on this forum, and found there was more that could be done.
Here is a picture of one of the original RTA 12's
I started by re-capping the crossovers, and then picked up an entire set up MW6600x drivers on eBay, along with a pair of the SW120 passives from an SDA. These do not have the dampener glued to the front like the original passives, and as you can see there was some separation on the front (of both) passives.
I picked up some Dynamat Extreme and Dynaliner on eBay to dampen the driver baskets and line the inside of the cabinets. Here are a few pictures of that work.
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I also rotated the passives and drilled new pilot holes in all eight spots, and used Mortite to set the passives. I have gaskets on the way for the MW's.
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How do they sound? The crossover upgrade was best described as taking cotton out of your ears. The subtle details were all much more noticeable. The bass seemed to be more defined as well. I did the crossover upgrades prior to the rest of the work to try and gauge the difference.
With the Dynamat Extreme on the driver baskets and Dynaliner in the cabinet, with about 50% fill, the mid-range has really seemed to open up. I read the expression "cupped hands" by another RTA12 owner, and that 'cupped hands' mid-range feel is gone.
What Next...... ? The plan is to strip the vinyl off the cabinets, and replace it with real Cherry Veneer in High Gloss. I am also making custom stands with spikes (also Cherry) which will look like part of the speaker and set them at the right height. The pair I have are actually for Monitor 10's and these sit a bit high. The base will be 5" high with 1" Spikes, and will be 3/4" wider all the way around than the cabinet. I am also making a custom hat, also in Cherry, that will be 5" tall and set 3/4" narrower than the cabinet itself. The tweeter will mount similar to a 12B, but will only have the silk dome and 4 inner mounting screws visible. The new 'hat' will angle away on each side of the tweeter at about 30 degrees. The back will be open to allow airflow and backside reflection (if any exist) from the tweeter out.
The 12B's employed a metal diffuser at about a 30 degree angle mounted under the tweeter. My plan is to do the same with some 1/8" Chery backed with Dynamat. If I can, I am going to burn the PolkAudio Logo into the cherry wood diffuser before mounting it. Since the tweeter will be removed from the back, I can permanently mount this diffuser.
I am still thinking about how to have a Cherry face instead of black - may laminate that as well and leave the grill covers off. When all is said and done these should look fantastic and sound exceptional. Total height should be 41".
First, I have an overhaul on a Carver M500t to finish!