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  1. #1

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    Default RTA15 Modifications

    I am less than excited to see that none of the images work in my post. Anyway, you can head over to my Picasa album to see the pictures that are mentioned in the post.

    http://picasaweb.google.com/jimiles/PolkRTA15Rebuild#

    Thanks to everyone on the forum for inspiring me to get serious about modifying my pair of RTA15TL speakers. I am the original owner of these speakers. I bought them in 1994 at Great Sounds in Muncie Indiana while I was attending Ball State.

    Disassembly

    There are approximately one billion screws in a pair of RTA15s, so getting everything out of the cabinet is a non-trivial affair. I cannot begin to stress how important it is to label everything before you take it apart. I also highly recommend only disassembling one speaker at a time, so you have a fully assembled, functioning reference. Here is what the cabinet looks like when empty. You can see the tape I used to label every connection, and the bowl I used to collect the screws.



    Secret Sauce

    The first modification to the cabinet was to paint it the interior with Cascade VB-1X damping compound.



    This attenuates panel resonances nicely. One gallon is more than enough to do both cabinets. Shave your arms or put on a long sleeved shirt before applying this substance! Be patient, and let each coat dry before applying the next. Trust me, you'll want the break!



    Crossovers


    There is an intermediate step not pictured in which you pour over the Polk forums and Tony Gee's cap shootout on the internet at work for weeks trying to decide what brands of components to use. It's vastly superior to doing actual work while you are at work. ;)

    Here are my components on scrap piece of MDF. You need to decide on a layout. Obviously your new components are multiple orders of magnitude larger than the old ones, so they aren't going on that tiny little PCB screwed to the input cup. In a later step, we'll rip that off and throw it away!


    Remember that the cutout for the front passive radiator is only 9 inches, and your crossover has to fit through that opening. The input cup is in the back, and the drivers are in the front, so try to arrange the input and output sides of your crossover with that in mind.

    I mounted my components to a piece of maple 1x6. I probably obsessed over the stain on my board a little too much considering that it goes inside the speaker never to be seen again! There are more high-tech ways to fasten the components to the board, but I got-back-to-basics with my hot glue gun.



    Wiring

    Though I didn't take a picture of it, remember to connect all of the pigtails that go to up to the drivers and out to the terminal cup when you are wiring the crossovers. Now would be a good time to assemble your new wiring harnesses, also. Use the old one as a template to create the new one. The original Polk factory instructions for assembling the harness can be downloaded from forum if you'd like an additional technical reference.

    I used Neotech solid-core teflon insulated wire to make new harnesses. I used exactly the specified gauge for the tweeter. I slightly increased the gauge of the woofer harness, since they see far more power on average than does the tweeter. I used exactly the specified lengths.

    Terminal Cup

    This requires more attention than you might think. First you need to remove the old crossover. There are four screws holding it in place. Remove those, and then snip all of the wires to get it free. Then comes the fun part; removing the binding posts from the cup. The nuts on the back are covered by a giant dollop of hot glue to prevent them from turning when the binding posts are tightened. Scrape away the glue to expose the nuts. I opened the binding post all the way, inserted a small screwdriver through the speaker wire opening, then used my socket to remove nut inside the cup.

    Depending on how insane your new binding posts are, you may need to drill out the holes in the terminal cup to accept them. My Cardas rhodium posts fell squarely into that category.

    After tremendous profanity and a half gallon of Diet Dew, the binding posts were installed as pictured below.



    Do not tighten the nuts down with your nuclear impact wrench! Later, you'll need to remove the nuts to mount the ring terminals of the crossover pigtails.

    Though I lacked the vision to do it; I hope that someone out there is man/woman enough to use the extra space on the terminal cup to mount a second set of binding posts. Since you are wiring the crossover point-to-point, a second set of posts is the only thing standing between you and all of your wildest bi-wiring/bi-amping fantasies!

    Cabinet Part II


    I lined the inside of the cabinets with a 1.125 inch foam/vinyl barrier product similar to BlackHole. This provides even more panel damping, and the works to attenuate flutter echo inside the cabinet. Most importantly, it absorbs some of the woofer's backwave. Remember; there's just as much energy radiating off the back of the speaker cone as the front. The backwave bounces around inside the cabinet and eventually passes out through the cone. This delayed copy of the signal wrecks accuracy in the time domain. Attenuate the backwave with the foam/vinyl barrier panels as pictured below.



    The vinyl layer has the consistency of floor tile, which makes the panels fairly rigid, and your knife fairly dull Panels are self-adhesive, and the adhesive is serious stuff. Test fit each piece before removing the backing to expose the adhesive. If you had any arm hair left after the VB-1 application, its about to come off during this step :( Here's one cabinet very nearly complete.



    Final Assembly

    Slide your crossover into the bottom of the enclosure first. Connect the pigtails to the terminal cup, then begin installing and connecting the drivers. When complete, use a 9v battery to confirm that all of the drivers are wired in phase. Do NOT connect the speaker to your amplifier until you verify the impedance of the speaker. Use your multimeter to confirm that it is approximately 7.5 ohms. Once you are satisfied with the phase and impedance, then connect the speaker to your amplifier. Start at a very very very low volume and increase it gradually until you are satisfied that nothing is going to explode.

    Your speakers will sound like smashed dog turds until everything burns-in. Do not do any critical listening at this point. Now would be an excellent time for you to travel to your neighborhood mini-mart for a cola product of your choice. :D

    Mods not pictured

    I also installed the new silk dome tweeters from Polk If you have the SL3000 tweeter like my RTA15s, it'll be a tasty little improvement. If you have one of the older tweeters, it'll be like God reached down and healed your speakers.

    My RTAs now ride on Vibrapods mounted to 2 inch Cusinart end-grain cutting boards. This serves to uncouple the speakers from the floor. When the speakers are spiked to the floor, bass travels through the cabinet walls, through the spikes, and into the floor. The floor is a very efficient bass radiator, because it has massive surface area coupling it to the air in the room. A very small amount of cabinet resonance can produce significant output through the floor. This is a way, way, way bigger deal than it might seem. If you are looking for something you can do without opening up your speakers, the Vibrapods are cheap and the improvement is massive.

    Thanks for all of the support, and good luck to everyone who decides to take the plunge and modify their vintage Polks.

    Let me know if I can help in any way

    Party On!
    Jake
    Last edited by jimiles; 09-26-2008 at 01:11 AM. Reason: Image links don't work

  2. #2

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    I am interested in Neotech solid-core teflon wire. Where did you find it?
    Nice complete write up.
    Thanks Ben
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben

  3. #3

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    Default Neotech

    Quote Originally Posted by ben62670 View Post
    I am interested in Neotech solid-core teflon wire. Where did you find it?
    Nice complete write up.
    Thanks Ben
    Hi Ben,

    I got the Neotech from PartsConnexion. It's great stuff, and you won't be disappointed

    I wish I knew more about inserting photos into my post. I used the insert picture button, and pasted the URL for pictures in my Picasa web album that I wanted. Obviously that's not how it works

    Thanks!
    Jake

  4. #4

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    Default

    I just went to PartsConnexion and checked it out. $3.29 a foot for teflon solid copper 16ga. I really want to rewire these.
    http://www.polkaudio.com/forums/showthread.php?t=53273
    I have 16 MW's in each cabinet:( It's a lot of stinken wire!
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben

  5. #5

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    Default

    If you preview, you'll lose the pics.

    Anyway, a few thoughts. Make sure you recover the backside of the binding post plates with hotglue to help prevent air leaks. That same backwave is what drives the PR's, so damping it will likely reduce bass output.
    '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 turd by the clean end."

  6. #6

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    Default

    Quote Originally Posted by ben62670 View Post
    I just went to PartsConnexion and checked it out. $3.29 a foot for teflon solid copper 16ga. I really want to rewire these.
    http://www.polkaudio.com/forums/showthread.php?t=53273
    I have 16 MW's in each cabinet:( It's a lot of stinken wire!
    Your custom SDA Polkensteins melted my brain. I'd estimate that you'll need approximately ten miles of wire for those. Periodically, PartsConnexion will have a 20% off sale, but 20% off of a bagoogagillion dollars, is still a ton of coin for wire. It took 50 feet to do my RTA15TLs.

    Party On,
    Jake

  7. #7

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    Default

    Quote Originally Posted by F1nut View Post
    If you preview, you'll lose the pics.

    Anyway, a few thoughts. Make sure you recover the backside of the binding post plates with hotglue to help prevent air leaks. That same backwave is what drives the PR's, so damping it will likely reduce bass output.
    I previewed....I lost the pics. :p

  8. #8

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    Default Parts List

    Here is a parts list of everything I used and where I bought it.

    Jantzen Z-Superior capacitors from PartsExpress
    Obbligato capacitors (copper-case version) from Diyhifisupply
    Obbligato capacitors (film/oil version) from Diyhifisupply
    Jantzen foil inductors from PartsExpress
    Duelund silver-graphite resistors from PartsConnexion
    Neotech solid core teflon wire from PartsConnexion
    Cardas rhodium plated binding posts from PartsConnexion

    Once again, I apologize for the misfire on the pictures in my main post.

    Thanks!
    Jake

  9. #9

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    Default Pictures!!!

    Well crap...still no pictures.

    <table style="width:auto;"><tr><td><a href="http://picasaweb.google.com/lh/photo/v8zR9XxXx3Q3LdmMsQerFw"><img src="http://lh6.ggpht.com/jimiles/SNxPU4KuJwI/AAAAAAAABMk/RlqdE6jHtxY/s144/DSC00225.JPG" /></a></td></tr><tr><td style="font-family:arial,sans-serif; font-size:11px; text-align:right">From <a href="http://picasaweb.google.com/jimiles/PolkRTA15Rebuild">Polk RTA15 Rebuild</a></td></tr></table>
    Last edited by jimiles; 09-26-2008 at 02:05 AM.

  10. #10

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    Well I found them. Those XO's are awesome! The site appears to have linking disabled?
    I can't even post a link to your pic hosting site?
    Ben
    Last edited by ben62670; 09-26-2008 at 01:53 AM.
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben

  11. #11

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    Default

    Thanks Ben, glad you like the crossovers :)

    I went into Picasa and changed my default setting to allow every kind of sharing under the sun, but I still don't think it works properly.

    http://picasaweb.google.com/jimiles/PolkRTA15Rebuild#
    Last edited by jimiles; 09-26-2008 at 02:10 AM.

  12. #12

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    It could be Polk blocking it?
    Do you have Photobucket?
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben

  13. #13

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    I see pics :)
    '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 turd by the clean end."

  14. #14

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    Default

    Quote Originally Posted by F1nut View Post
    I see pics :)
    Like the Sixth Sense, "I see dead people!"

  15. #15

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    Default

    Quote Originally Posted by ben62670 View Post
    It could be Polk blocking it?
    Do you have Photobucket?
    I don't have Photobucket, but I may investigate it tomorrow. F1 says he sees the pictures?!?

  16. #16

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    I do when I click on the link in #11.

    Get Photobucket, no worries.
    '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 turd by the clean end."

  17. #17

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    Default Neotech

    Quote Originally Posted by ben62670 View Post
    I just went to PartsConnexion and checked it out. $3.29 a foot for teflon solid copper 16ga. I really want to rewire these.
    http://www.polkaudio.com/forums/showthread.php?t=53273
    I have 16 MW's in each cabinet:( It's a lot of stinken wire!
    One downside; the Neotech wire I used only comes in one color per gauge. This makes the wiring process tedious. Another funny thought about Neotech; teflon is a fantastic insulator, but it also is one of the worlds slickest substances. The wire is actually a little difficult to hold onto while stripping and cutting. :p

    I almost used the cotton insulated hookup wire from Duelund (available at Partsconnexion). It was similar in price, so if anybody chooses to go that route, let me know how you like it!

  18. #18

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    Link in 11 works for me.
    I know about the Teflon. I use where ever I can. It is worth the money;)
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben

  19. #19

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    Nice write-up. I can see the photo's from link #11 as well. Nice work with some premium components. SO............how do they sound??? Details please.

    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 Aleph 30; Eastern Electric Mini Max; Adcom GDA600; MIT S3/Z Pc; SDA 1C; Squeezebox; Tubes add soul!

  20. #20

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    That Neotech wire is also available from Sonic Craft. I used it to re-wire my Tannoys. And yes, it is slick. :D It helps to hold the other end with needle nose pliers when stripping.

    Btw, nice job!
    "He who fights with monsters should look to it that he himself does not become a monster. And when you gaze long into an abyss the abyss also gazes into you." Friedrich Nietzsche

  21. #21

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    I have to get a SoniCraft catalog. The wires selection literally made me drool
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben

  22. #22

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    Default Oh, I forgot to tell you what they sound like.

    Quote Originally Posted by heiney9 View Post
    Nice write-up. I can see the photo's from link #11 as well. Nice work with some premium components. SO............how do they sound??? Details please.

    H9
    Thanks H9! How do they sound? The speakers really get out of the way, making difference between good and bad recordings painfully obvious.

    The bass is much less omnipresent. In stock form, there was previously a hump somewhere in the lower registers that is completely gone now. Deep bass seems stronger, though typically that perception results from fixing some other problem in higher registers. Bottom line; putting the speakers up on the Vibrapods absolutely revolutionized the bass. Guys/gals with concrete slab floors might not experience quite such a transformation, but I implore everyone to try it.

    Midrange is smoother. The foam/vinyl barrier step fixed that. A guy on the Partsexpress product review forum said that peaks in midrange response were cut in half when he did some before/after measurements. My ears tell me that he was probably telling the truth.

    Treble is less tizzy, and I know for a fact that most of that is the result of the silk dome tweeter from Polk. Hats off to the guys who designed it! Harmonics are more accurate. The decay after attacks on cymbals and piano are much more realistic.

    The macro and micro dynamics are both better. The sound remains coherent at higher volumes, and yet the quiet little details are there in spades, too.

    I did the write up as a tutorial, but I really did the work in about five stints over the course of the winter. The other thing that clouds my memory of the stock speakers is that I rebuild the crossovers three years ago with Solen/Mills components. So, when I got done with this rebuild I felt like the improvements were incremental, but exactly what I wanted. Had I jumped from bone stock to this level, I probably would have been blown away.

    As an epiloge to my modding experience; I just started addressing my room acoustics. The gains to be had in acoustics utterly dwarf the differences between some of the other things we debate endlessly here on the forums. That is in no way to say those differences are not real and important, but my first three acoustic panels have opened my ears to what the big problems really are.

    I've broken down into a full blown ramble at this point!

    Party On,
    Jake

  23. #23
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    Great write-up and fantastic job on the rebuilds/mods!

  24. #24

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    Default Thanks!

    Quote Originally Posted by zingo View Post
    Great write-up and fantastic job on the rebuilds/mods!
    Hey man, thanks for the vote of confidence.

    I just posted a couple of pictures of the speakers back in their natural habitat for anyone who wants to check out the fruits of my labor

    http://picasaweb.google.com/jimiles/...5ZNyS8Fxm4dRw#

  25. #25

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    Nice work Jake
    Whats next?

  26. #26

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    Default The question of the day!

    Quote Originally Posted by NJPOLKER View Post
    Nice work Jake
    Whats next?
    Thanks for vote of confidence!

    Next in general; a 44 oz Diet Dew will be guzzled. ;)

    Audio; I bought three open back 4" acoustic panels. Two are straddling the front corners as bass traps, and one is directly behind the listening position. I am hooked on acoustics now :D I bought some raw Owens Corning 703 and I'm planning to roll a few of my own. The difference between an untreated room and even a mildly treated room is amazing.

    I've had a subwoofer under construction for well over a year now. Its a passive sub with a single Polk SR124-DVC driver that I plan to drive with the third channel of my Aragon 8008x3. I am so sick of routing mdf, that I could barf. I'm about 75% finished, but I just can't bring myself to work on it right now. So don't hold your breath waiting to see that one finished.

    http://picasaweb.google.com/jimiles/Subwoofer#

    As for the RTA15s; I want to finish treating the room and integrating the subwoofer into the system before I open them up again.

    I already posted another thread asking for ideas about a more sophisticated crossover. Obviously the stock topology was chosen to keep the part count down and hit a production budget. Maybe a tweeter zobel, maybe higher order slopes, I really have no idea where to invest?!? I'm rapidly nearing the point where I need to install some design software, measure the driver parameters, and model some things before I break out the power tools again.

    One concept that's been floating around in my head for quite sometime is electrically damping the passive radiators. Instead of just using a weighted cone with spider, you install a complete driver, but instead of connecting it to the amplifier, you simply put a resistor across the terminals. Theoretically this gives you all of the impedance benefits of a passive radiator, with much better impulse response. Sonus Faber uses this techinque to great effect in many of their speakers. Obviously, if I do a subwoofer this becomes a moot point.

    Do you have an projects cooking?!?

    Party On
    Jake
    Last edited by jimiles; 09-26-2008 at 04:19 PM.

  27. #27

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    Very nice job on the speakers and nice pics....but whats up with the bath towel under the TV ;)
    The first rule of Fight Club is you don't talk about Fight Club

  28. #28

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    Default How dare you question genius?!?

    Quote Originally Posted by shadowofnight View Post
    Very nice job on the speakers and nice pics....but whats up with the bath towel under the TV ;)
    That's....ummm....a special acoustic bath towel

    Thanks for the vote of confidence on the mods!

    Party On :)
    Jake

  29. #29

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    Do you have an projects cooking?!?

    Party On
    Jake

    Again, nice work. The only project I have working now is painting my kitchen.
    Over the winter I may do something to my SRSII's but then again I may just sit back and enjoy them. I have already re-done the x-overs and have the RDO's so I am kinda set for awhile.
    Drew

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    Jake,
    Very good write-up on a thorough, well-done project. I'm sure they really sing now!

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