Polk RTA 12 B Overhaul
Michael8it
Posts: 192
Here are a few pictures of my overhaul project. I started with a pair of Polk RTA 12 cabinets that were in average condition. The plastic laminate covering was torn off one side of one cabinet, but other than that they were in good shape. I decided to finish the cabinets in Cherry, and build custom bases for them to sit on. I also decided to move the crossover inside the cabinet and make customer mounts for the tweeters, leaving them uncovered. I also did all the 'standard' modifications such as hurricane nuts to mount the drivers, extra bolts in the PR, dynamat on the driver baskets, new seals all around, rebuilt crossovers, dynaliner in the cabinets, new posts on the back, and JB weld on the magnets. I'm probably going to bite the bullet and buy some Black Hole 5 to place behind the drivers as well.
For the cabinets, I wanted to go with a furniture look. The cabinets are a box, and all they are ever going to be are a square box. So I took my design cues from Mission style furniture, which I like, and which deals nicely with a square box look.
In the pictures below, we have finished all the rough work and have them stained. I have yet to decide if I am going to fabricate a speaker grill of some kind, or if I am going to just leave them open. I don't have any kids running around so that is not a major concern.
The next two phases will be a few coats of sealer, then several coats of lacquer. I'll post more pics as we progress.
For the cabinets, I wanted to go with a furniture look. The cabinets are a box, and all they are ever going to be are a square box. So I took my design cues from Mission style furniture, which I like, and which deals nicely with a square box look.
In the pictures below, we have finished all the rough work and have them stained. I have yet to decide if I am going to fabricate a speaker grill of some kind, or if I am going to just leave them open. I don't have any kids running around so that is not a major concern.
The next two phases will be a few coats of sealer, then several coats of lacquer. I'll post more pics as we progress.
Carver C-1, M-500 MKII, Yamaha HTR-5835, Polk RTA 12BM's (M-for mod'd).
Comments
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Polk Mission editions.....nice.Don't take experimental gene therapies from known eugenicists.
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Very cool.
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Well that is unique and stylish. Will the bases be attached or will they just sit on them? Do you have room on the feet for spikes?
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The speakers will sit on the stands on a very thin piece of open cell foam ( so I don't tear up the base and to keep it from sliding around. The were designed to have spikes. Holes have been drilled but I will install those at the last step.Carver C-1, M-500 MKII, Yamaha HTR-5835, Polk RTA 12BM's (M-for mod'd).
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Why not attach them to the base? I think they look good together. Won't the foam inhibit bass transfer to the floor?
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The foam is 1/16th on an inch thick, just enough to prevent scratching. I added 3/4" plywood to the bottom before I started finishing them to add some mass at the bottom. The spikes will de-couple the speakers from the floor so permanently mounting the speakers to the base to get bass to transfer to the floor would seem to be a moot point. The base is completely open underneath so if it turns out that permanently mounting them to the base is the best way that is still an option.Carver C-1, M-500 MKII, Yamaha HTR-5835, Polk RTA 12BM's (M-for mod'd).
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Nice! I like the false through tenons on the bases.
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Nice! I like the false through tenons on the bases.
That was my brother Tom's idea. I liked it!
I could not have done this project without him. Plus a friend works at a fabrication shop and was able to cut the tweeter mounts on a CNC machine so they are perfect.Carver C-1, M-500 MKII, Yamaha HTR-5835, Polk RTA 12BM's (M-for mod'd). -
Very nice, anxious to see the finished product!
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Very impressive!!
Follow your heart, and do what makes you happy. Looks great. -
Sweet! Tweeter mounts look awesome. Whole project is awesome. Nice shop also. Lol.
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Wow! I never thought of that. I have a pair but they're the "A" version. I was planning on moving them on but I might reconsider.
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If you can get B/C crossover you can convert them, which is what I did.Carver C-1, M-500 MKII, Yamaha HTR-5835, Polk RTA 12BM's (M-for mod'd).
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Beautiful.
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Nice woodwork.
I assume you are mounting the tweeter exactly the same as stock since these are a "real time array" speaker? Also I wonder about the fact that tweeters now have a bezel around them with a lip, might affect dispersion.
If the dispersion and tweeter characteristics are altered they will no longer be time aligned and that could hurt the awesome performance of these speakers.
H9"Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass Pass Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Pangea AC14SE MKII | Legend L600 | BlueSound Node 3 - Tubes add soul! -
Enough to decouple the speaker from the stand.Michael8it wrote: »The foam is 1/16th on an inch thick, just enough to prevent scratching.
Spikes couple, not decouple.Michael8it wrote: »The spikes will de-couple the speakers from the floor
Ideally the speakers are coupled to the floor, to prevent the speaker cabinet from moving due to the motion of the driver(s). Adding a sheet of foam is a mistake. -
Great idea and first class work. I can't wait to see the finished job.
Schurkey is correct about the spikes.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
Nice woodwork.
I assume you are mounting the tweeter exactly the same as stock since these are a "real time array" speaker? Also I wonder about the fact that tweeters now have a bezel around them with a lip, might affect dispersion.
If the dispersion and tweeter characteristics are altered they will no longer be time aligned and that could hurt the awesome performance of these speakers.
H9
Yes, I took several measurements to make sure the tweeter wound up in the exact same spot. I knew moving it would be an issue.Carver C-1, M-500 MKII, Yamaha HTR-5835, Polk RTA 12BM's (M-for mod'd). -
Schurkey, thanks for the info. I will have to find a way to mount the base to the cabinet and allow for disassembly for transporting. I think I have that figured out. I'll also need to finish the plywood on the bottom so it does not tear up the base when I mount/dismount it.
Carver C-1, M-500 MKII, Yamaha HTR-5835, Polk RTA 12BM's (M-for mod'd). -
Looks great ! I especially like the tweeter mount and diffraction plate. Makes me want to do this to my 12C's."Science is suppose to explain observations not dismiss them as impossible" - Norm on AA; 2.3TL's w/sonicaps/mills/jantzen inductors, Gimpod's boards, Lg Solen SDA inductors, RD-0198's, MW's dynamatted, Armaflex speaker gaskets, H-nuts, brass spikes, Cardas CCGR BP's, upgraded IC Cable, Black Hole Damping Sheet strips, interior of cabinets sealed with Loctite Power Grab, AI-1 interface with 1000VA A-L transformer
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Here are some updated photos. I had some issues with the veneer bubbling up that I could not resolve, so I will live with that for now. Finish is not quite what I wanted but again, I will take it for now. Working on the internal wiring and waiting for my polyfill to arrive. The cabinets are not currently mounted to the base, but there is enough weight on them for now, and I will look at how to bolt them together later.
I'm particularly happy with the tweeter mounts. These were made from reclaimed cherry and I think they look fantastic.
I also put in t-nuts on the drivers and the passive woofer. I think I will do this for the crossover on the back as well. I upgraded the posts and the wiring as well.
After looking at them assembled I wish I had made the base a bit taller. Still happy with them though as they stand a few inches taller that the original 12B's.
Carver C-1, M-500 MKII, Yamaha HTR-5835, Polk RTA 12BM's (M-for mod'd). -
They look very nice! I'm curious what effect the edges you've introduced will have on the sound.
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They look very nice! I'm curious what effect the edges you've introduced will have on the sound.
Hopefully none. The original grill these came with was raised the same distance, it was just covered in cloth so you could not tell. I hope to finish the wiring this weekend and fire them up.Carver C-1, M-500 MKII, Yamaha HTR-5835, Polk RTA 12BM's (M-for mod'd). -
Very nice!
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Beautiful work. You inspire us all with your greatness! Peace. DMIT Magnum MH-750, Monster HTS 5100MKII, Sony 77" Class - A80CJ Series - 4K UHD OLED,PS4, Def Tech 15” sub,LSIM 706c, Sunfire Signature Grand 425 x 4,Parasound hca 120, LSiM 702 x 4, Oppo 103D, SDA SRS 1.2, Pioneer Elite SC63 , Pioneer Elite BDP-05 “Why did you get married if you wanted big speakers?”
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I'm having a challenge re-wiring these. The schematic I have shows the + side as black wires, and the - as white, but that does not appear to be how these were originally wired. If someone who has a pair could take some photos of where the leads are coming off the top crossover for the mid and tweeter I would appreciate it.
I know the tweeter is wired out of phase because of the distance to the drivers, but the driver wiring does not seem to line up with the schematic either.
Thanks,Carver C-1, M-500 MKII, Yamaha HTR-5835, Polk RTA 12BM's (M-for mod'd). -
yes, the black wires are + in the vintage polks like my CRS+'s & SDA 2B's and the monitor 10's. and on all 3 of these the black wire is positive for the tweeters also.
I don't know about the others like yours.
my crossovers
2 ch- Polk CRS+ * Vincent SA-31MK Preamp * Vincent Sp-331 Amp * Marantz SA8005 SACD * Project Xperience Classic TT * Sumiko Blue Point #2 MC cartridge
HT - Polk 703's * NAD T-758 * Adcom 5503 * Oppo 103 * Samsung 60" series 8 LCD -
Black is positive. I believe that the tweeters get reversed in the XO so that is why they are wired out of phase at the tweeter.
At least that was my understanding.
I could 180* wrong
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I did a quick peek inside my 10a and I noticed one black wire connected to a white wire! Didn't have time to trace where everything went yet but that was definitely confusing. I hope no one was messing with the internals.
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I did a quick peek inside my 10a and I noticed one black wire connected to a white wire! Didn't have time to trace where everything went yet but that was definitely confusing. I hope no one was messing with the internals.
I think I'm running into the same issue. I am going to go with what the schematic shows and ignore the wire colors I see.Carver C-1, M-500 MKII, Yamaha HTR-5835, Polk RTA 12BM's (M-for mod'd).
