Modifications to the RTA 15TL

[F1nut]

Al, there was a model RTA 11T. You could get it in any color as long as it was black.

[decato]

You have an early release of the RTA 15TL. You can tell by
1) The large, circular circuit board used in the crossover.
2) The use of a 1.5 ohm rather 2.0 ohm resistor in the high-pass filter.
3) The convex rather than flat dustcaps on the drivers.
4) The lack of side braces in the cabinet.

[BSUfbfan]

You have an early release of the RTA 15TL. You can tell by
1) The large, circular circuit board used in the crossover.
2) The use of a 1.5 ohm rather 2.0 ohm resistor in the high-pass filter.
3) The convex rather than flat dustcaps on the drivers.
4) The lack of side braces in the cabinet.

Gotcha! kinda confusing though... even the owners manual says 15T. Maybe originally they were going to designate anything with the trilaminate just with a "T".

My drivers are the same as yours though... MW6503's & passive's with the flat dustcaps.

You're right, it did have the 1.5 ohm resistor, and I swapped it out for a 2.7 as per the schematic and it seems spot-on.

[F1nut]

even the owners manual says 15T

Interesting! That's the first I've heard of that one.

[Face]

Interesting! That's the first I've heard of that one.

I found a pair locally some time last year, the owner was asking $650 firm. I believe he claimed the box had RTA-15T written on it. I should contact him again and see if he came down on his price and to confirm no L.

[heiney9]

In the end the important thing is these have always used the sl3000 tweeter which is the better tweeter compared to the sl2000. The "T" and "TL" designation is a minor issue and a typical Polk "mystery".

Thanks Decato, I'll be adding you precise info about the 15's to my internal database. :)

H9

[decato]

The earliest advertisement I can find for the RTA series is from the October 1987 edition of Audio Magazine. The title reads The Genius of Matthew Polk Towers Over the Competition. Therefore, I believe the t in RTA 8t and 11t (and the very first release of the 15 we are discussing in this thread) stood for tower. I guess this is how they differentiated the original Monitor 11 from the new tower design with the same number. Interestingly, this ad shows what we know as the RTA 8t as the RTA 11t! I have attached a PDF of this ad.

The second generation of RTAs were labeled TL, after the new SL3000 trilaminate tweeter.

-Brian

[BSUfbfan]

Here is the RTA-15T addendum that was inserted into the owners manual for the RTA-11T & RTA-8T. It states that the 15T has the Polk SL-3000 trilaminate. hmmmm.

[BSUfbfan]

Well, after @90 hours of break in I sat infront of the 15's today and ran through a bunch of my favorite CD's.... Very impressive. The overall frequency response from top to bottom is much smoother now! Also with the raised crossover point on the tweeter, the speakers take a lot more volume before distortion, in fact, with my 200wpc Aragon I reached half volume and the Polks played extremely loud without a pop or a crackle.

My CRS+ definitely have a wider, more defined soundstage, but I think the 15's have a fuller sound in the midrange/midbass......nothing like having 8 drivers :p. Overall this crossover upgrade is a no-brainer for the cost (<$200 for tweeters, caps, coils, resistors), and I feel is a must for the 15TL owner that is planning on an upgrade to the RDO tweeters.

[decato]

That's great! I am glad to hear that you are pleased with the modifications.

[acerjac]

Decato,

I am thinking about modding my 15's with the same layout as you came up with. I am new to this and am wondering what you think of just replacing the cap's and resistors? I would leave the stock inductors alone.

Thanks for your opinion.

[decato]

I am new to this and am wondering what you think of just replacing the cap's and resistors? I would leave the stock inductors alone.

If you wish to perform the modification, at the very least you will need to change the inductor in the high-pass section of the crossover. BSUfbfan did this and was pleased with the results. Be sure to use the mod from 03-29-2008.

[acerjac]

I replaced all the caps and resistors on my crossovers on my 15's and oh my what a difference. I used a combination of solens and clarity caps. A quick question though, I used a 2.5 ohm resistor instead of the stock 1.5 ohm. They sound great but I am just wondering if it is something to consider. Thanks

Mark

[Face]

I replaced all the caps and resistors on my crossovers on my 15's and oh my what a difference. I used a combination of solens and clarity caps. A quick question though, I used a 2.5 ohm resistor instead of the stock 1.5 ohm. They sound great but I am just wondering if it is something to consider. Thanks

Mark

The 1.5ohm resistor and 12uf cap are part of a contour circuit, which is used to flatten the response curve. It may not make a night and day difference, but I would replace it with the correct resistor when you have a chance.

[decato]

A quick question though, I used a 2.5 ohm resistor instead of the stock 1.5 ohm. They sound great but I am just wondering if it is something to consider.

The 2.5 ohm resistor will reduce the tweeter's output at the lower end of its operating range. I have attached images of the crossover's transfer function with a 1.5 ohm and 2.5 ohm resistor in the circuit.

[acerjac]

You guys are great

[acerjac]

Where do you get this information? Are you doing these curves yourself?

[decato]

Where do you get this information? Are you doing these curves yourself?

I use LspCAD to generate these graphs.

[acerjac]

I replaced the 2.5 resistor with the 1.5 and a clarity cap sa in place of the solen. The sound is smoother on top. The clarity cap does a great job in the high pass filter.

[phandnot]

How would this x-over upgrade work with the SL-3000 left alone? Would this even be a good idea? Just curious.
Also, I have the RTA-15TL model, but the boxes they came in new have RTA-15t on the side.



Weird.

[acerjac]

By that you mean you would leave the high pass circuit alone correct? If you are going through the trouble of rebuilding the x-overs why not do the whole thing? It would only make the sl- 3000 tweeters sound better. My speakers have the upgraded tweeters and they sound great with the x-over rebuild. As for the T vs TL issue, it is discussed above. I think my boxes say TL on them.

Mark

[phandnot]

What I meant was, will the x-over upgrade/rebuild work without upgrading the tweets, and left my SL-3000s in there. Or does the upgrade just work better with the RDOs. I do like the sound of a good silk dome...

As far as the T - TL thing goes, I know there is no difference, I was just including a picture of the "T" boxes to show that they do exist! Mine say T on the box, but the speakers themselves show the correct TL.

Any info on the tweets will help!

Thanks.

[ben62670]

The upgrade would work for either tweeter.

[F1nut]

Weird.

Not really. Polk used up whatever excess materials they had around, be it boxes, labels, cabinets, etc.

[skrol]

Here is an interesting tidbit of information regarding the RTA15T that came from the designer when I asked him about the RTA15T vs TL. They were likely renamed as the RTA8T and RTA11T were upgraded to TL and it may detract from RTA15T sales. It is interesting what goes into choosing a name. From the designer:

"...I guess marketing changed the name later to TL. ... Original RTA8 and RTA11 had different tweeter ... new tweeter SL3000 came up just before I started design on RTA15T. So RTA15T started with tri-laminate tweeter ... but 8 & 11 went from T to TL when they were upgraded. Your assumption is correct RTA15T and RTA15TL are the same.

RTA15 was originally being scheduled and introduced as RTA14, I worked on it as RTA14 ... we had some literature printed ... when one day national sales manager came and said stop, stop, can't call it RTA14 ... he learned from Asian distributor that number "four" means on Chinese "death" and that we wouldn't sell any speaker ... (after RTA11 we didn't want to call it 12 because of Monitor 12, didn't want to call it 13 because of western superstition, couldn't call it 14 because of Chinese superstition and the next number was 15)"

[LPN]

Superstitions play into model numbers? ... interesting. I guess the 9-11 designation would never come to be.

Cheers, Barrie.

[skrol]

The superstition has even played a role in the design of buildings and factories. Many buildings skip the 13th floor. I saw a program where some Chinese factories have 5 smoke stacks instead of 4 even if the fifth is a dummy.

I guess the Germans are not superstitious. They still make Porsche 911's.

[decato]

How would this x-over upgrade work with the SL-3000 left alone? Would this even be a good idea? Just curious.

No, I have tried the SL3000 with the modified crossover, and it does not sound as good as the RD0198-1.

[acerjac]

Hey does anyone know where I could get the inside cabinet dimensions for the srs 3.1's? I would like to build a pair.

Mark

[rhubarb9999]

I have a pair of 15TLs that I like a lot. I have found the top end to be a little 'in your face' and the bass a little muddy. I fix some of that with EQ, but I am interested in trying the mods in this thread.

I have all the parts from a set of Monitor 10a's. The tweaks mention using the PRs from the Monitor 10 and 10b .. is the 10a different?

Also, I have the Peerless tweeters out of the 10a's. Would these be a suitable upgrade to the 3000 tweeters that are currently in the 15TLs?

Thanks