Modifications to the RTA 15TL
decato
Posts: 188
Introduction and Goals
The RTA 15TL was Polk’s top of the line non-SDA model, manufactured from 1990-1992. It features a vertical array of drivers with the tweeter positioned in the center, a configuration known as MTM or D’Appolito, named after its designer Dr. Joseph D’Appolito. The cabinet houses two independently tuned passive radiators, one “high-resonance” in the front and one “low-resonance” in the rear.
After quite some time, I finally got around to working on the RTA 15TL. I listened to them with the stock crossover parts and SL3000 tweeters before making any modifications. I concluded that the tweeter was working pretty hard, probably due to a low crossover point, which made some recordings sound harsh, especially those with a saxophone or electric guitar. Even some vocalists came across with an unpleasant timbre. It also sounded as though the tweeter was a bit too loud, or forward. I had some spare RD0198-1 tweeters lying around, so I gave them a try. To my surprise, they actually sounded worse overall! They were cleaner but even more strident.
The bass of the RTA 15TL was not what I expected. I measured the response of both passive radiators and observed that they have similar output, except that the “low-resonance” one always puts out 3-4 dB less than the “high-resonance” one. (Julian Hirsch reviewed the RTA 15TL in December 1990 and measured a 5 dB variation in output levels. I have attached a PDF of this review for you to read.) I also noticed that the speakers boomed dreadfully when placed close to a wall. There was an excess of midbass, especially in the 100-200 Hz range, but output below 100 Hz was noticeably less. My hypothesis on the abundance of boomy midbass is as follows:
While this type of bass is great for reproducing organ pedals, whose sounds rise and fall slowly, it is less than desirable for almost everything else.
So, I can sum up my evaluations as follows: I like the sound of the RTA 15TL. I think that it can be made to sound even better with some effort. The crossover design could benefit from a little tweaking, and I would like to try a few tricks to improve the bass.
Parts and Procedures
The original design of the crossover (Figure 1) yields the transfer function you see in Figure 2, assuming a DC resistance of 6.8 ohms for the 4 MW6503 drivers in a series-parallel configuration and 5.6 ohms for the single RD0198-1 tweeter. After several iterations of design and evaluation, I have modified the crossover schematic to that of Figure 3, with the new transfer function shown in Figure 4. I did not make a “drastic” alteration but rather a subtle change to the slopes. The tweeter does a bit less work, while the woofers’ high end rolls off more gradually. The crossover point has been shifted up several hundred Hz. The tweeter's phase is pretty close to that of the woofers.
The parts needed for this project came from the following vendors at a total cost of $201.50 + shipping:
[LIST=4]
[*]RD0198-1 (SL3000 Replacement) Tweeters
Polk Audio
1-800-377-7655
www.polkaudio.com
Madisound Speaker Components, Inc.
608-831-3433
www.madisound.com
Sonic Craft
1-800-689-4434
www.soniccraft.com
Wayne Electronics
973-839-5888
Local craft store
The two SW105 passive radiators are, unfortunately, priceless. I have a few spare parts that I collected over the years packed away in boxes. I'll talk more about the passive radiators shortly.
The following figures show how the crossover looks with the new components in place. Sorry, but most of the labeling has been worn off the capacitors from conducting too many experiments.
The new components are significantly larger than the stock parts and require a new layout. The thick gauge 1.75 mH inductor is probably the least useful of the modifications, resulting in just about 1 dB more bass at very low frequencies. Eliminating this component makes the modification easier (and less costly), as no change to the layout is required. I have not tried more expensive capacitors, but I have tried Daytons. I cannot recommend using them, as they sound “lifeless”.
To reduce the muddiness of the bass, I added 2 extra sheets of damping material behind the drivers and 1 extra sheet in the center of the cabinet behind the front-firing passive radiator. As mentioned earlier, the “low-resonance” passive radiator has less output than its sibling, so I removed it from the cabinet. Then I moved the SW100 from the front to the back and installed a lightweight SW105 (used in the Monitor 7 and 10 Series 2) to the front. I obtained a 3 dB boost in bass below 60 Hz and lost 2 dB around 150-200 Hz with this modification. I wish I had detailed specifications about the various passive radiators to scientifically justify my observation.
To improve imaging while simultaneously masking a defect in the vinyl around the tweeter, I cut out a foam pad and gently attached it to the area around the tweeter with a glue stick.
Finally, I applied 3 coats of Tung oil to the veneer.
Question: Why are the speakers sitting in the lids of plastic containers?
Answer: To avoid scratching the floor more than I already have!
Listening Evaluation
I am quite pleased with how this modification turned out. The midrange tonality is more natural, the bass is fuller, and the tweeter output is no longer abrasive. By using Solen capacitors, I have experienced the same improvements as many other forum members, so there is no need to describe those sonic changes here. The RTA 15TLs cast a beautiful center image if toed-in properly. The imaging is, indeed, very close to that of the SDA series, except that sound never comes from the far left or right of the soundstage. I still recommend keeping them as far away from walls as possible.
Does this mean that I am 100% finished with this project? No. Those of you who know me recognize that I am almost never fully satisfied with my projects. I always tend to revisit them, especially when new information becomes available or I learn a better method to solve a problem. In this case, my next goal is to obtain more detailed information about the drivers, tweeter, and passive radiators. However, for now, it is time to sit back and enjoy the music!
- Brian Borowski
The RTA 15TL was Polk’s top of the line non-SDA model, manufactured from 1990-1992. It features a vertical array of drivers with the tweeter positioned in the center, a configuration known as MTM or D’Appolito, named after its designer Dr. Joseph D’Appolito. The cabinet houses two independently tuned passive radiators, one “high-resonance” in the front and one “low-resonance” in the rear.
After quite some time, I finally got around to working on the RTA 15TL. I listened to them with the stock crossover parts and SL3000 tweeters before making any modifications. I concluded that the tweeter was working pretty hard, probably due to a low crossover point, which made some recordings sound harsh, especially those with a saxophone or electric guitar. Even some vocalists came across with an unpleasant timbre. It also sounded as though the tweeter was a bit too loud, or forward. I had some spare RD0198-1 tweeters lying around, so I gave them a try. To my surprise, they actually sounded worse overall! They were cleaner but even more strident.
The bass of the RTA 15TL was not what I expected. I measured the response of both passive radiators and observed that they have similar output, except that the “low-resonance” one always puts out 3-4 dB less than the “high-resonance” one. (Julian Hirsch reviewed the RTA 15TL in December 1990 and measured a 5 dB variation in output levels. I have attached a PDF of this review for you to read.) I also noticed that the speakers boomed dreadfully when placed close to a wall. There was an excess of midbass, especially in the 100-200 Hz range, but output below 100 Hz was noticeably less. My hypothesis on the abundance of boomy midbass is as follows:
Both passive radiators, despite their different moving masses, operate over the same basic range. However, they are out of phase with each other. If placed close to a rear wall, the waves from the backward-firing passive radiator will hit the wall and be reflected toward the front, now in phase with the front-firing passive radiator but slightly delayed, resulting in slow, boomy bass.
While this type of bass is great for reproducing organ pedals, whose sounds rise and fall slowly, it is less than desirable for almost everything else.
So, I can sum up my evaluations as follows: I like the sound of the RTA 15TL. I think that it can be made to sound even better with some effort. The crossover design could benefit from a little tweaking, and I would like to try a few tricks to improve the bass.
Parts and Procedures
The original design of the crossover (Figure 1) yields the transfer function you see in Figure 2, assuming a DC resistance of 6.8 ohms for the 4 MW6503 drivers in a series-parallel configuration and 5.6 ohms for the single RD0198-1 tweeter. After several iterations of design and evaluation, I have modified the crossover schematic to that of Figure 3, with the new transfer function shown in Figure 4. I did not make a “drastic” alteration but rather a subtle change to the slopes. The tweeter does a bit less work, while the woofers’ high end rolls off more gradually. The crossover point has been shifted up several hundred Hz. The tweeter's phase is pretty close to that of the woofers.
The parts needed for this project came from the following vendors at a total cost of $201.50 + shipping:
[LIST=4]
[*]RD0198-1 (SL3000 Replacement) Tweeters
Polk Audio
1-800-377-7655
www.polkaudio.com
2 x RD0198-1, $96 (with Club Polk discount)
[*]Solen PB Series Film Capacitors and Air Core InductorsMadisound Speaker Components, Inc.
608-831-3433
www.madisound.com
4 x 12 uF, $20
2 x 10 uF, $9
2 x 1.75 mH, 16 awg, Sidewinder, custom-wound $30
2 x 0.3 mH, 19 awg, inductor, $5.90
[*]Mills MRA-12 Resistors2 x 10 uF, $9
2 x 1.75 mH, 16 awg, Sidewinder, custom-wound $30
2 x 0.3 mH, 19 awg, inductor, $5.90
Sonic Craft
1-800-689-4434
www.soniccraft.com
2 x 2.7 ohms, $7.00
2 x 0.5 ohm, $7.00
Fee for order less than $25, $5.00
[*]Waldom Universal Connector2 x 0.5 ohm, $7.00
Fee for order less than $25, $5.00
Wayne Electronics
973-839-5888
2 x 628-6, $10
[*]Foam Sheets and Damping MaterialLocal craft store
2 foam sheets, $1.60
Large bag of polyester sheets for a baby’s crib, $10
[/LIST]Large bag of polyester sheets for a baby’s crib, $10
The two SW105 passive radiators are, unfortunately, priceless. I have a few spare parts that I collected over the years packed away in boxes. I'll talk more about the passive radiators shortly.
The following figures show how the crossover looks with the new components in place. Sorry, but most of the labeling has been worn off the capacitors from conducting too many experiments.
Figure 5: RTA 15TL Crossover with Waldom Connector (makes experimenting easier)
Figure 6: RTA 15TL Crossover, Topside View
Figure 7: RTA 15TL Crossover, Underside View
Figure 6: RTA 15TL Crossover, Topside View
Figure 7: RTA 15TL Crossover, Underside View
The new components are significantly larger than the stock parts and require a new layout. The thick gauge 1.75 mH inductor is probably the least useful of the modifications, resulting in just about 1 dB more bass at very low frequencies. Eliminating this component makes the modification easier (and less costly), as no change to the layout is required. I have not tried more expensive capacitors, but I have tried Daytons. I cannot recommend using them, as they sound “lifeless”.
To reduce the muddiness of the bass, I added 2 extra sheets of damping material behind the drivers and 1 extra sheet in the center of the cabinet behind the front-firing passive radiator. As mentioned earlier, the “low-resonance” passive radiator has less output than its sibling, so I removed it from the cabinet. Then I moved the SW100 from the front to the back and installed a lightweight SW105 (used in the Monitor 7 and 10 Series 2) to the front. I obtained a 3 dB boost in bass below 60 Hz and lost 2 dB around 150-200 Hz with this modification. I wish I had detailed specifications about the various passive radiators to scientifically justify my observation.
Figure 8: Dense Damping Material behind Drivers
Figure 9: Damping Material in Bottom of Cabinet
Figure 10: Front-firing SW105 Passive Radiator
Figure 11: Rear-firing SW100 Passive Radiator
Figure 9: Damping Material in Bottom of Cabinet
Figure 10: Front-firing SW105 Passive Radiator
Figure 11: Rear-firing SW100 Passive Radiator
To improve imaging while simultaneously masking a defect in the vinyl around the tweeter, I cut out a foam pad and gently attached it to the area around the tweeter with a glue stick.
Finally, I applied 3 coats of Tung oil to the veneer.
Figure 12: Foam Pad around Tweeter
Figure 13: RTA 15TL Front Baffle
Figure 14: Tung Oil Finish
Figure 13: RTA 15TL Front Baffle
Figure 14: Tung Oil Finish
Question: Why are the speakers sitting in the lids of plastic containers?
Answer: To avoid scratching the floor more than I already have!
Listening Evaluation
I am quite pleased with how this modification turned out. The midrange tonality is more natural, the bass is fuller, and the tweeter output is no longer abrasive. By using Solen capacitors, I have experienced the same improvements as many other forum members, so there is no need to describe those sonic changes here. The RTA 15TLs cast a beautiful center image if toed-in properly. The imaging is, indeed, very close to that of the SDA series, except that sound never comes from the far left or right of the soundstage. I still recommend keeping them as far away from walls as possible.
Does this mean that I am 100% finished with this project? No. Those of you who know me recognize that I am almost never fully satisfied with my projects. I always tend to revisit them, especially when new information becomes available or I learn a better method to solve a problem. In this case, my next goal is to obtain more detailed information about the drivers, tweeter, and passive radiators. However, for now, it is time to sit back and enjoy the music!
- Brian Borowski
Post edited by decato on
Comments
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Very impressive work! It's always interesting to me when enthusiasts of the hobby boldly step out and try some advanced teaking or mods. If you were to do this again, would you do anything different?
How do you thin these sound like compared to the RTA-12's?
Congrats on your work! Enjoy!
CarlCarl -
schwarcw wrote:If you were to do this again, would you do anything different?
I probably will do it again one day! Without more detailed information about the frequency response of the drivers, their impedance, and their Thiele-Small parameters, there's not much more you can do.schwarcw wrote:How do you think these sound like compared to the RTA-12's?
They are totally different. I had the RTA-12, that is, the 1980 version that you placed on a stand. While its treble was so clear and clean and its imaging very precise, its mids were nasty. I recall colorations somewhere between 250-500 Hz. I never bothered modding them. I was 16 when I bought them used and sold them shortly after that. That might be an interesting project for someone, but the crossover is 4th order, so it will be more costly to do experimentation. -
Brian, as usual, a nice job.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 -
great work,very impressive , enjoyJC approves....he told me so. (F-1 nut)
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Very nice indeed!
What kind of software did you use for your simulations and plots?
CarlCarl -
schwarcw wrote:What kind of software did you use for your simulations and plots?
LspCAD -
Very nice and interesting. I also have the RTA15TL's. They always sounded like something was missing to me. I was wondering at what frequency your crossover points are.
Thanks
BenPlease. 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 -
ben62670 wrote:I was wondering at what frequency your crossover points are.
Hi Ben,
The theoretical crossover points for the original design and my modification are 1390 Hz and 1700 Hz, respectively. I say "theoretical" because my model uses only the DC resistance of the drivers and tweeter, not the impedance curves. -
I was over at Brian's house this afternoon, and the speakers truly do sound awesome. I had the privilege to hear them before and after the modifications. Pre-modifications, they arguably sounded worse than a set of monitor-10's he has. Post-modifications, they beat the monitor-10s hand down.
:cool:
:eek: :mad: :rolleyes: -
semeesee wrote:I was over at Brian's house this afternoon, and the speakers truly do sound awesome. I had the privilege to hear them before and after the modifications. Pre-modifications, they arguably sounded worse than a set of monitor-10's he has. Post-modifications, they beat the monitor-10s hand down.
:cool: :eek: :mad: :rolleyes:
I find that hard to believe. The first part anyways......the Monitor 10, while the model that may have put Polk on the map, is not a great speaker design. The D'appolito array in the RTA-11 and RTA-15 in stock form are far superior to the Monitor 10 and it's side by side drivers. The RTA-15 is twice the speak the Monitor 10 is comparing stock to stock.
I have no doubt the mods done to the RTA-15's are both substantial and make a huge difference. But to say a stock pair of M10's sounded better than stock RTA's is just ludicris.
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! -
The 10s have also been modified, and they did sound better than the 15s to start out with.
-
So this is not a case of Franken-Polk?Lexicon Toshiba Crown EAW
-
The 10s have also been modified, and they did sound better than the 15s to start out with.
I'd love to hear about the monitor 10 mods.
I have a set and will probably get around to replacing the electrolytic caps one day.The world is full of answers, some are right and some are wrong. - Neil Young -
To all who are interested, here is the way I have been running the RTA 15TLs for the last 8 months. The design is quite similar to what I described in the first post, except that I backed off on the mids a little bit more. In general, the sound is still detailed but doesn't get fatiguing. It's tricky... Reducing the amount of inductance on the LP section just seems to make the woofers play louder rather than causing them to play higher frequencies, so there's not much one can do in that section of the crossover. Reducing the inductor in the HP section provides a steeper slope, thus reducing the low end of the tweeter. I think the D'Appolito design was meant for 3rd order crossovers, but there is not enough space on the board, nor do I have the time to experiment with even more components.
Tip: If you can feel the surface of the tweeter vibrating along with a vocal or sax solo, the crossover point is too low.
That's a lot of movement for a small diaphragm, and it will naturally increase distortion and sound harsh. The original crossover point is low, around 1500 Hz. And since it uses a 0.4 mH inductor, it's also a gradual slope. Hence, almost every pair of RTA 15TLs you see on the the used market will have a blown tweeter.
So, the new parts list is as follows:
2 x 13.5 uF (2 x 12 uF + 2 x 1.5 uF) caps
2 x 12 uF caps
2 x 10 uF caps
2 x 1.75 mH, 16 awg inductors
2 x 0.22 mH, 19 awg inductors
2 x 2.7 ohm resistors
2 x 0.5 ohm resistors
As for bass, the RTA 15TL is unique. It's not going to deliver the same fullness as the SDA series. It goes low but sounds like some waves are canceling (due to the forward- and rear-firing passive radiators). Don't bother taking apart working Monitor speakers for the passive radiators. You can just leave the original passive radiators in place. If you do leave them alone, do not add any additional damping material. Just make sure that the original amount is lining the sides and back of the cabinet.
Also, make sure the tweeter is rewired out of phase.
FYI, this system consists of a modified Apt Holman preamp (new caps and op amps), an Apt A1 amplifier, and a NAD C542 CD player. If you try these modifications, please post back with your opinions. -
Have you considered taking a few coils off the main inductor to help raise the MW's XO point?
Thanks BenPlease. 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 -
Have you considered taking a few coils off the main inductor to help raise the MW's XO point?
Thanks Ben
I tried something similar with the Monitor 10 Series 2. The RTA 15TL is 8 ohms, and I use 1.75 mH and 13.5 uF. For the 10, which is 4 ohms, you might think 0.875 mH and 27 uF will give exactly the same crossover point. Theoretically, yes. However, it does not sound right at all. So, I do not believe it's a good idea to reduce the inductance for the RTA 15TL. However, you will see I reduced the capacitance from 20 uF to 13.5 uF. Since the rolloff is more gradual with less capacitance, you get a few more highs out the of the drivers. (Off course, the phase changes. Nothing is free.)
Do you have another inductor lying around? Maybe you can just solder it in place of the original one instead of making an irreversible change. -
Thanks for the heads up on that Brian. I do have some extra XO's I have picked up on my travels. I did notice the changed value in the cap. I was thinking about doing a changer to a wmtmw, and placing the XO point on the upper, and lower woofers at around 200hz. Readers please note this is an experiment, and not a suggestion till results are verified.
Thanks again.
BenPlease. 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 -
I think putting a $3 cap on the tweeter will solve all problems.
H9
P.s. I hope this post isn't selectively targeted to be deleted like many of my other posts in the past 2 days :rolleyes:"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! -
Keep on topic please. Thanks.CTC BBQ Amplifier, Sonic Frontiers Line3 Pre-Amplifier and Wadia 581 SACD player. Speakers? Always changing but for now, Mission Argonauts I picked up for $50 bucks, mint.
-
Well, finally got the RTA-15T upgrade completed today... The speakers are currently in burn-in, but I just had to take a listen after getting them put back together. I can already hear a major difference in the treble, so I am very excited to hear them after the ClarityCaps get a proper break-in.
When I got them taken apart, I was surprised to see that the 15-T model has a different crossover layout than the later 15-TL. The Crossover and the tweeters were stamped "15T", but all 8 drivers were stamped "SDA-CRS+"... interesting.
Thanks to Brian (Ducato) for taking the time to really tweak this crossover, and posting the associated documentation.
Here are a couple of pics of the cleaned up 15T's and the very busy crossover board.
SDA SRS 2.3 -
RTA 15T's?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 -
Yup.
I always end up with the weird ****. Like the ultra-rare blade/blade CRS+
All of the Crossover spec's are still the same as the 15-TL, the thing is just built different. The CRS+ stopped production in 1989, and these were manufactured in May of 1990, so they must have used all the left-over SDA-CRS+ drivers in the early production run....
The sticker on the midrange magnet actually states "This driver designed for the SDA-CRS+", and they stamped a red "15T" over the top of it.SDA SRS 2.3 -
The drivers with a stamp for a different model is not uncommon, believe it or not.
What was the original tweeter in your RTA 15T?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 -
-
No such thing as an RTA 15 "T". I realize the schematic and driver is labeled that way but that's just what happens with Polks sometimes.
Since it had the sl3000 tweeter which is a Trilaminate material (hence the TL designation) it's a "TL".
As far as I'm aware the RTA 15 model was in production *after* Polk stopped using the sl2000. Never heard or seen an RTA 15 T. Your is a "TL" because of the trilaminate tweeter used.
SDA's which are "TL" don't have a designation on the label or drivers most of the time."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! -
Forgot to say nice work!!! You'll really enjoy the benefits of a x-over refresh.
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! -
Yup.
I always end up with the weird ****. Like the ultra-rare blade/blade CRS+
All of the Crossover spec's are still the same as the 15-TL, the thing is just built different. The CRS+ stopped production in 1989, and these were manufactured in May of 1990, so they must have used all the left-over SDA-CRS+ drivers in the early production run....
The sticker on the midrange magnet actually states "This driver designed for the SDA-CRS+", and they stamped a red "15T" over the top of it.
Another thing I was thinking is maybe originally they intended to make an RTA 15 "T" but by the time it hit production they had made the switch from the sl2000 to sl3000 tweeter in other Polk models. The sl2500 was actually manufactured after the sl3000. It's my understanding they were not both introduced at the same time. (the sl3000 and sl2500 being the (2) Trilaminate tweeters)"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! -
They were the SL-3000
Ok, thanks. H9's response is correct, there never was a RTA 15T.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 -
if there was a "T" model.. what would it have stood for? temporary? "tricked" ?
I too have never heard of a 15T model. so maybe you got luck and have the 15TL's instead. PolkFest 2012, who's going>?
Vancouver, Canada Sept 30th, 2012 - Madonna concert :cheesygrin: -
Al, there was a model RTA 11T. You could get it in any color as long as it was black.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
