Help me plan/troubleshoot my 11TL crossover redo

agfrost

Hi all,

I've been planning to redo the crossovers in my RTA 11TLs for some time--actually, I bought Sonicaps/Daytons/Mills for myself as a Christmas gift. Well, my schoolteaching year came to an end on Wednesday, so I finally got down to the business of taking a serious look at what I'm to be doing.

I pulled both crossovers, and immediately noticed that one is labeled "RTA 8T" while the other is "RTA 11T." I've been around here long enough not to panic when seeing such a thing, we all know how Polk loves to use its parts bin.

However, a closer look showed that the "8T" crossover has a 2 ohm resistor in it, while the 11T has the 1.5 ohm shown in the 11TL schematic. I looked at the schematics for the 11TL, 8TL, and 11T--both the 8TL and 11T have the 2 ohm resistor, but the 11T has an additional 2.7 ohm resistor that I don't have, so I've ruled out the possibility that I may have an 11T crossover.

Comparing the 8TL schematic to the 11TL schematic, I see two differences: the resistor value and that the value for the smaller inductor is 0.4 mH on the 8TL and 0.3 mH on the 11TL. I hadn't planned on doing anything with inductors on this project, but do I have to, on the chance that I've got a complete 8TL crossover?

OK, I've proven my theory that I can say in 500 words what others could in 100, but I'd appreciate any and all thoughts and advice you may have before I proceed.

Thanks,

Jay

ben62670

I would use the 2ohms in place of the 2ohm, and 1.5ohm. Where is the 2.7ohm? What tweeters do they have? Take a DCR reading of both inductors. It will tell you how close they are. They may have just used a "spare" board. Take your time on this one. I am sure the Polk mind bank can set this straight.
Ben

heiney9

I would call Ken at Polk and discuss. The difference between the 1.5 and 2.0 ohm is negligible and probably why they used it in the first place; parts bin I'm sure. I'd still ask Ken why yours are different than the schematic and ask him which in his opinion you should go with.

As a side note: This is why you shouldn't always buy the parts before you pull the x-overs. .

Where's the other resistor?

H9

P.s. If it were me I'd go with the schematic since you already have the parts. Since the values are close, I doubt there would be much difference.

agfrost

Thanks for the replies.

I've the 11TL, whose crossover only uses a single (1.5 ohm) resistor. I've already been using the RD0-198 tweeters.

Ben, realizing that I could use/don't have a DCR meter explains why I'm (at least temporarily) paralyzed on this.

Brock, there is only the one resistor on each board. Here's the links for the two crossover schematics in question:

11TL

8TL

The summary: Both have the same number of parts, the same location of those parts, but different values for the resistor and one of the two inductors. Obviously my driver complement is that of the 11TL, with the RD0's and MW6510 mids.

My plan is to make each match the schematic for the 11TL, and the one thing that is preventing me from easily doing so is not knowing the value of the smaller inductor installed in my "curious" crossover. I will contact Ken for his opinion.

Thanks,

Jay

heiney9

Ah, I missed the "TL" part in the thread. Got all caught up in the labels on the actual x-overs.

skrol

Wow, that is interesting. Are you the original owner? Maybe Polk CS will be kind enough to give you the correct XO.

heiney9

skrol wrote: »

Wow, that is interesting. Are you the original owner? Maybe Polk CS will be kind enough to give you the correct XO.

Polk always used things from the parts bin. Like I said earlier the .5 ohm difference is probably not even noticeable. The thing that threw me is the RTA11T label on the x-over cup. The parts are correct for the RTA11 TL x-over sans the 1.5 ohm resistor.

My bet is they ran short on RTA11 TL x-overs that particular day and threw in an RTA8 TL x-over to get the speakers off the line.

Again a 0.5 ohm difference with 10% tolerance parts wouldn't be noticeable.

H9

agfrost

heiney9 wrote: »

Polk always used things from the parts bin. Like I said earlier the .5 ohm difference is probably not even noticeable. The thing that threw me is the RTA11T label on the x-over cup. The parts are correct for the RTA11 TL x-over sans the 1.5 ohm resistor.

My bet is they ran short on RTA11 TL x-overs that particular day and threw in an RTA8 TL x-over to get the speakers off the line.

Again a 0.5 ohm difference with 10% tolerance parts wouldn't be noticeable.

H9

What about the potential that the smaller inductor could be 0.4 mH versus 0.3 mH? I confess that I don't know the purpose of the inductors, so I can't imagine whether or not the difference is important.

Jay

skrol

I did a quick PSpice simulation of the RTA11T and RTA11TL OX's to show the differences. This is using a resistive 8ohm loads and not a reactive speaker loads. The RTA11T OX is based on the schematic marked (REV) and the RTA11TL is based on my original XO's.

[Deleted User]

Hello,
I checked with Stu Lumsden and Scott Orth, in the engineering department, and they both agree that you should build your new crossover to the original RTA 11TL specifications. Also, the inductors should be matched, hopefully by measuring the inductance directly. If you want you are able to send parts to us and we will measure them for you, at no charge.
Scott feels that 0.5 Ohms is a significant difference in resistor values and would be audible.
Regards, Ken

heiney9

Good info Ken. Glad to get some feedback about the 0.5 ohm resistor difference. I have a modded pair of 5B's w/Solen caps and Mills resistors and the RD0194-1 tweeter. I ended up purchasing 2.0 ohm resistors and put those in where 2.7 ohm resistors were originally. I've often wondered how much the 0.7 ohm difference affected the tweeter output.

These use fuses for tweeter protection not poly switches. I assume the poly's may add a bit of resistance to the circuit, hence the use of 2.0 ohm resistors when the poly switch was in place for later 5B versions. Is that a correct assumption?

Probably should put in the correct 2.7 ohm resistor.

Thanks

H9

agfrost

Thank you for your input, Ken. Your advice matches my desire, to get both to correct 11TL specs. My main issue was ensuring that the inductors matched, and now you've given me a greatly appreciated way to take care of that! I'll be in touch.

Jay

Big Dawg

Any update? Curious minds want to know.....

agfrost

Thanks for the curiosity, Dawg. I'll drop the particulars...

I sent the xovers to Polk, they were tested and the odd one was in fact a 8TL crossover. Polk found a similar inductor, but it matched the one on the 8TL xover. I gave the OK to put it onto the 11TL crossover, but now I'm having 2nd thoughts...

1st, because I've decided I want the correct 0.3 mH coil on, rather than matching incorrect-spec coils, and 2nd, because I didn't ask for my old inductor back--This leaves me with a problem, I can't measure the DCR of the stock 11TL inductor.

I PM'd one 11TL owner, but I'll throw out this question to anyone tuned in: Anybody got a 11TL crossover upon which they can measure the DC resistance across the smaller inductor coil, or happen to know the value? I've been searching on the net looking for possible suitable ones, but without the stock resistance, I'm hesitant to buy... I found possible replacements at Solen and at Vertek I'm pretty sure I want the 20 gauge coils, but again, if anybody knows better...

This project is going about typically for me: Slow, and with a lot of overthinking. I may start a new thread appealing to 11TL owners if this doesn't draw any advice for me.

Jay