Original RTA-12 Upgrades/Tweaks
Jazzhead
Posts: 533
Hi Folks, I'm new to this forum, although I have checked it out in the past. Back in 1980 I bought my pair of original RTA-12's with 12 inch "Polk Stands". I started making some improvements to these several months ago, and after contacting Polk on a related matter I was told that they would greatly benefit from a crossover upgrade. That got me in contact with westmassguy (DHS Speaker Service), who has been extremely generous to me with his time, knowledge and advice. I'm sending the crossovers to him after the holidays (gotta have our tunes) and am looking forward to hearing new Sonicaps and Mills resistors etc.
I have the original Polk sales flyers/materials and the RTA-12 User Manual in case anyone is interested. Here's what I have done so far:
I upgraded the binding posts by mounting some Cardas silver/rhodium posts in some thick 6 inch aluminum discs that I had fabricated at a local machine shop. I sprayed the discs black and used the screw holes from the stock binding post cups as the screw template. I didn't use the original cups as they were cracking at the screw holes (35 years - yikes). The results were audible, dynamic and positive, with speakers that sounded pretty good to start with. The stock binding posts were connected to the internal wiring with lugs that were bolted to the posts (not soldered) and hot glued. Apparently the connection had degraded/oxidized over time.
These speakers have the crossover/tweeter assembly that sits on top of the speaker. The Peerless tweeter is positioned back a bit for time alignment purposes. The crossover sits on a thin layer of foam affixed to the top of the cabinet. I wanted to further isolate the crossover from cabinet vibrations so I cut identical sized sheets of 1/8 inch damping material from Herbie's Audio Labs (the same footprint as the foam) and placed this between the foam and the crossover. This cleared up some of the "smear" in the music. A definite improvement.
The Polk Stands I filled with dense sand, and then epoxied them together (they originally bolted together), and gave them a new coat of paint. They work very well with this speaker as they position the tweeter at ear height when sitting. A tweak that is definitely worth mentioning is that these speakers really like sitting on four Herbie's Audio "Big Fat Dots" (between the speakers and the stands). They just come alive. Especially in the lowest frequencies. The speaker stands themselves are sitting on four Herbie's Gliders, which use the same decoupling material as the Dots. My house has a wood floor over a full basement and the Herbie's stuff prevents the low frequency sound from traveling through the floor, reaching the listening position and muddying things.
I pulled the drivers last weekend and epoxied the magnets. I wanted to get that done before I got the crossovers back. As I wrote westmassguy - I didn't want Art Blakey to shift a magnet while I was breaking in the new caps...
I am planning to install Blackhole5 or Sonic Barrier behind the woofers, Dynamat on the PR and drivers, re-seal the cabinet, install new gasket foam, and westmassguy has also advised me to get all the polyfill re-positioned above the passive radiator. I am intending at some point to replace the internal wiring with heavier gauge UPOCC wire as well. I'll share what I learn along the way, and would appreciate any and all advice. Thanks.
I have the original Polk sales flyers/materials and the RTA-12 User Manual in case anyone is interested. Here's what I have done so far:
I upgraded the binding posts by mounting some Cardas silver/rhodium posts in some thick 6 inch aluminum discs that I had fabricated at a local machine shop. I sprayed the discs black and used the screw holes from the stock binding post cups as the screw template. I didn't use the original cups as they were cracking at the screw holes (35 years - yikes). The results were audible, dynamic and positive, with speakers that sounded pretty good to start with. The stock binding posts were connected to the internal wiring with lugs that were bolted to the posts (not soldered) and hot glued. Apparently the connection had degraded/oxidized over time.
These speakers have the crossover/tweeter assembly that sits on top of the speaker. The Peerless tweeter is positioned back a bit for time alignment purposes. The crossover sits on a thin layer of foam affixed to the top of the cabinet. I wanted to further isolate the crossover from cabinet vibrations so I cut identical sized sheets of 1/8 inch damping material from Herbie's Audio Labs (the same footprint as the foam) and placed this between the foam and the crossover. This cleared up some of the "smear" in the music. A definite improvement.
The Polk Stands I filled with dense sand, and then epoxied them together (they originally bolted together), and gave them a new coat of paint. They work very well with this speaker as they position the tweeter at ear height when sitting. A tweak that is definitely worth mentioning is that these speakers really like sitting on four Herbie's Audio "Big Fat Dots" (between the speakers and the stands). They just come alive. Especially in the lowest frequencies. The speaker stands themselves are sitting on four Herbie's Gliders, which use the same decoupling material as the Dots. My house has a wood floor over a full basement and the Herbie's stuff prevents the low frequency sound from traveling through the floor, reaching the listening position and muddying things.
I pulled the drivers last weekend and epoxied the magnets. I wanted to get that done before I got the crossovers back. As I wrote westmassguy - I didn't want Art Blakey to shift a magnet while I was breaking in the new caps...
I am planning to install Blackhole5 or Sonic Barrier behind the woofers, Dynamat on the PR and drivers, re-seal the cabinet, install new gasket foam, and westmassguy has also advised me to get all the polyfill re-positioned above the passive radiator. I am intending at some point to replace the internal wiring with heavier gauge UPOCC wire as well. I'll share what I learn along the way, and would appreciate any and all advice. Thanks.
Comments
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Which midwoofers do the originals use? I wonder if you could have had the crossovers modded so that the two drivers roll off at different frequencies like the later RTA-12s to reduce comb filtering.afterburnt wrote: »They didn't speak a word of English, they were from South Carolina.
Village Idiot of Club Polk -
The B & C revisions have a split crossover, the main crossover is on top, with a separate Low Frequency Module behind the Binding Post Cup. Inductor and Capacitor values or different as well.Which midwoofers do the originals use? I wonder if you could have had the crossovers modded so that the two drivers roll off at different frequencies like the later RTA-12s to reduce comb filtering.Home Theater/2 Channel:
Front: SDA-2ATL forum.polkaudio.com/discussion/143984/my-2as-finally-finished-almost/p1
Center: Custom Built forum.polkaudio.com/discussion/150760/my-center-channel-project/p1
Surrounds & Rears: Custom Built forum.polkaudio.com/discussion/151647/my-surround-project/p1
Sonicaps, Mills, RDO-194s-198s, Dynamat, Hurricane Nuts, Blackhole5
Pioneer Elite VSX-72TXV, Carver PM-600, SVS PB2-Plus Subwoofer
dhsspeakerservice.com/
