3.1TL HF Circuit vs 4.1TL HF Circuit

markamerica

Hi folks! As usual, I'm looking for some guidance, and I'm hoping somebody here can provide it.

The 3.1TL and the never-produced 4.1TL have somewhat different circuits. Both use a single SL3000/RDO-198. The differences I can spot are these:

The 3.1TL uses a .3mH inductor coil, and it uses a 1.3ohm resistor in parallel to a 12uF capacitor, whereas the 4.1TL uses a .4mH inductor coil and it uses a 2.7ohm resistor in parallel with a 5.8uF capacitor. Both have the usual 12uF capacitor and 750pf capacitor in parallel although on one, this arrangement is before (the 3.1TL) and one is after the other cap in parallel with the resistor.

I always wondered about the apparent asymmetry of the 3.1TL, compared to the SRS, the 1s, and the 2s, and I wonder if this different set of values has to do with that. It seems to me like the SL3000 or the RDO-198 on a 3.1TL is having to work harder to stay in balance with 4 stereo and one dimensional MWs. 3.1TLs are one of the very few models I've never heard.

Can anybody explain this difference in single tweeter circuits in the TL models?

Thanks!

Mark

F1nut

Each circuit is designed to obtain a balanced sound, so what works in one may not work in another.

westmassguy

Mark, to further Jessie's point, the Resistor in Series with the Tweeter, and the overall resistance of the Shunt determine the crossover point and slope, as well as the SPL of the Tweeter. Same holds true for the DCR of the Inductors in Series with the Stereo and Dimensional Drivers. In addition, the Schematics are not always accurate. On my 2As for example, the Schematic shows #18 gauge for both the Stereo and Dimensional Inductors, when in fact, the Stereo Inductor was #18 gauge, and the Dimensional Inductor was #22 gauge. Big difference in DCR values versus the Schematics.

westmassguy

Mark, there's plenty of info on the web regarding crossover design, all the different types. There's also modeling software, which is much more accurate than the online calculators. Although Polk used 2nd order crossovers on most of the older models, their component values differ greatly from any of the online calculators. Polk heavily tweaked all the component values. They had or have an engineering department, specialized software, measuring equipment, sound rooms, etc.

markamerica

F1Nut, I guess that's what I figured. more or less. I guess I was always surprised that one tweeter could balance out 4 stereo and 1 dimensional as it does in the 3.1TLs.

Speaking of tweeters, i'm having a grand ol' time this evening.

markamerica

Westmassguy, Thanks, I could see where published specs not matching actual production could be a real headache. I've not run into that on anything yet. As to the point about the tweeters, I expected that answer, more or less. I'd like to learn more on this aspect, specifically crossover design. I'm still in my infancy in that regard, and as always, I always appreciate help!

Thanks!

Mark