Modifications to the RTA 15TL

[dorokusai]

Just buy the replacement silk dome tweeter and no, you cannot use the Peerless tweeter.

[F1nut]

I'm not sure about the PR deal, but the Peerless tweeter will not work. Get the RD0198-1.

LOL...Doro is faster on the keyboard.

[Face]

Purchase a pair of RD0-198's from Polk and upgrade the caps in your crossovers first.

[dorokusai]

I wouldn't put much weight in the PR suggestion and you'd be best served by the xover upgrade. The 15 has always sounded bloated, just like the equally bloated Moitor 12.

[decato]

Like the others have said, the Peerless tweeter will not work. I don't think it will fit properly in the cut-out. The mod was designed for the RD0198-1, so it probably won't sound right with the Peerless tweeter.

As for the passive radiators, it's not that big of a deal. Modifications to the crossover will definitely make a bigger impact. (I have since re-installed the original passive radiators.) I have not, however, made any changes to the crossover design that I posted on 03-29-2008.

Good luck with the mods. Let us know if you have any other questions.

[rhubarb9999]

Very good. I will probably just sell the Peerless tweeters to help fund the upgrade :)

I will order the parts this week and start tweaking.

Thanks very much.

[kcoc321]

I am still a novice at all this, but I noticed that the wiring diagram you posted shows the capacitor inline with the resistor as a "shunt" as in looping around the capacitor. Does/ would this change the performance curves you provided? I am just wondering because I have never seen this configuration. The Polk wiring diagram shows the Resistor 'Inline" with the capacitor "shunt" (if that is the right technical term)

Either way, very nice write up :D

[Face]

A resistor and capacitor in parallel is a Contour Network.

http://www.diyaudioandvideo.com/Calc...tour/Help.aspx

[kcoc321]

A resistor and capacitor in parallel is a Contour Network.

http://www.diyaudioandvideo.com/Calc...tour/Help.aspx

Thanks FACE, I was curious, because I have never seen one drawn up that way.
But then the only wiring diagrams I have studied are the Polk ones.

I am assuming it works the same either way?

[Ricardo]

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

I am ready to order the parts. What would be the impact of using 1.8 mH instead of 1.75 mH inductors?

Thanks.

[audiobilly]

Mistake reply, sorry.

[heiney9]

I am ready to order the parts. What would be the impact of using 1.8 mH instead of 1.75 mH inductors?

Thanks.

Catastrophic, world ending impact :D.

H9

[decato]

What would be the impact of using 1.8 mH instead of 1.75 mH inductors?

The difference is small. With a 1.8 mH inductor, the drivers will start rolling off at a slightly lower frequency. Nothing to worry about...

[FTGV]

What would be the impact of using 1.8 mH instead of 1.75 mH inductors?

No problem as thats well within tolerance but be sure the DC resistance (DCR)of the replacements are very close to the stock coils.

[Ricardo]

Brian,

Here's another question for you. I know nothing about xover design, so these are probably stupid questions.

Ok; so the original xover had a resistor of 1.5 ohm and the polyswitch. Since the polyswitch represents 0.5 ohms, the resulting R would be 2.0 ohms.
-When the polyswitch was removed, they changed the resistor from 1.5 ohm to 2.0 ohms, I assume to compensate for the missing polyswitch.

-Your design has a 0.5 ohm and a 2.7 ohm, which gives a resulting R of 3.2 ohm. Ok, I don't know if by having the capacitor in parallel with the resistor the resulting R is the same, but I will assume it is.

So isn't this design taming the highs too much? I know, I can try several resistors and see what happens, but wanted to know your perspective here.

Thanks.

[Ricardo]

Let me add this to the question above;

Would it be the same to have the 0.5 plus the 2.7 than just having a 3.2 in parallel with the capacitor?

Thanks.

[decato]

Hi Ricardo,

Let me add this to the question above;

Would it be the same to have the 0.5 plus the 2.7 than just having a 3.2 in parallel with the capacitor?

Thanks.

The original design has either 1.5 or 2.0 ohms in parallel with the cap. This RC circuit shaves off some of the tweeter's low end. It seems that the RD0198-1 goes lower than the SL3000 (or gets harsh if driven with too many midrange frequencies), so I increased it to 2.7 ohms.

The 0.5 ohm resistor in series with the whole tweeter circuit reduces the output evenly at all frequencies. Without this resistor I found the sound to be too bright. Keep in mind that my room has a hard floor. So, feel free to experiment. However, be sure to invert the polarity of the tweeter.

Please post again with your evaluation.

[Ricardo]

Thanks Brian Will definitely experiment and post back. And why is it that the polarity of the tweeter needs to be inverted?

[decato]

And why is it that the polarity of the tweeter needs to be inverted?

With second order crossovers, there is an approximate 180 degree difference between the phase of the high-pass and low-pass sections. Since the acoustic centers are (roughly) aligned, inverting the tweeter's polarity is the most common means of fixing this problem. Otherwise, a notch in the frequency response appears.

[Ricardo]

Thanks Brian. So was this a mistake in Polk's design, or is it your modifications that make this a requirement?
I just want to know if depending on the values of components I use, I should/should not invert the tweeters.

[decato]

So was this a mistake in Polk's design, or is it your modifications that make this a requirement?
I just want to know if depending on the values of components I use, I should/should not invert the tweeters.

I recommend inverting the polarity of the tweeters. However, you might as well try it both ways and pick what sounds best to you.

[Ricardo]

Got it. All parts were delivered today. Just need to find some free time to put everything together.

[Ricardo]

I FINALLY spent some time and made the changes.

From this neat little board:



To this ugly point to point mess :)



Breaking in. VERY promising from what I can hear. I have to say, these really look nice.

[MillerLiteScott]

You don't need subs with those 15's. Do you?

[Ricardo]

No; subs are off now. Plenty of bass on these.

[decato]

Glad your first impressions are positive. Drop us a line again after the break-in period is over.

(I see that you did not use the 0.5 ohm resistor in the tweeter circuit. If you feel the speakers are too bright, try out that extra resistor.)

[Ricardo]

Glad your first impressions are positive. Drop us a line again after the break-in period is over.

(I see that you did not use the 0.5 ohm resistor in the tweeter circuit. If you feel the speakers are too bright, try out that extra resistor.)

Adding/changing resistors will be easy, so yes, I will play a little with that.

And Brian, thanks for posting your work and findings to help the rest of us!!!

[Vette C6.r]

Good looking setup Ricardo.

[brgman]

Hello all.I am new to the forum and i find it is a unbelievable wealth of info.My question,should i consider it a crime to upgrade the tweeters and not do anything with the crossovers etc?
I do not have the tools or smarts to do it myself so is it a waste of money to just swap out the tweeters?
Thanks for any help in advance.

[Ricardo]

brgman, welcome to the club. It's a $100ish investment to just swap the tweeters. Most people like the new RDO's better than the SL3000's, so chances are you will also like them. But doing the xovers will bring you a significant improvement.

Just reporting after the caps have broken in (I would expect). These speakers (now) are among the best I've heard. Top to bottom balance, bass and 3D imaging is just incredibly good.
I do think they would benefit from that extra 0.5 ohm in the high's circuit, so I ordered new resistors. I am so impressed with the quality of the sound that I ordered Duelund's (will replace the 2.7 ohm too). I am confident these will benefit from the better quality.

Brian, once again thanks for sharing the outcome of your modifications. The speakers sound incredibly good. If someone offered me $3,000 I would not sell them!

Next step: Larry's rings should be here soon so I expect them to sound even better!