Polk Monitor 12 Schematics Question

Mystery

Looking at the Polk Monitor 12 schematics, the four mid woofers are wired not sure in series or parallel or both.

I was thinking two are in series and then each set is parallel like this:
|--O--O--|
|--O--O--|

But the schematic has one more connection in between without any shunt capacitor or anything:
|--O--|--O--|
|--O--|--O--|

So is that the same thing as two in series and then two sets in parallel but vertically ( in the diagram )?


|--O--|__|--O--|
|--O--|__|--O--|

canadianicon25

hmm..

not sure. -ve terminals of the upper pair and +ve terminals of lower are at the same potential due to the dead short connecting them. perhaps it has something to do with stabilization?

anyone understand this design?

Mystery

Looks like two drivers are in parallel first in 2 sets and then those 2 sets are in series.
Just the reverse of what I thought.
So if all drivers are 8 ohms, each parallel set will be 4 ohms and when those 2 sets are in series, total is 8 ohms.
Interesting as all drivers play the same thing without any crossover difference.

StantonZ

If you compare this schematic to the Monitor 10 schematic (something I'm more familiar with), it looks like 12's will present a higher impedance (to the amp) than the 10's. Where the 10's have (only) the 2 driver's in parallel for ~4 Ohms (even though we know it's a bit higher), the 12's add another pair to raise the impedance closer to ~8 Ohms. In addition, notice the cap in the bass leg of the 12's is about half the value of the one in the 10's. There are some other unusual differences as well, like the putting the poly-switch in parallel with ANOTHER cap; I replaced my PS with a 0.5 Ohm resistor and the high-end (on my 10's) sounds MUCH better.

JS1961

I've just run into the same confusion while trying to create a pair of 12's from scratch. Can anyone who has an original set confirm the the actual wiring harness matches the schematic? Or is this just a drafting error?
Thanks in advance,

westmassguy

There's no magic here. The 12's woofers are wired series/parallel. You have two groups of two. Each group of two can be wired in parallel (=4 ohms nominal), then the two groups are wired together in series (= 8 ohms nominal). Alternately, you can wire each group in series (= 16 ohms nominal), then wire the two groups in parallel (= 8 ohms). The result is the same, 8 ohms nominal.
On the low pass, in order to maintain the same crossover frequency, the Inductor is twice the value, and Shunt Capacitor is half the value of the Monitor 10s. This is do to the nominal impedance difference between the 10's two woofers at 4 ohms nominal, vs the 12s four woofers at 8 ohms nominal.
There are two Monitor 12 schematics, the original, and the revised.
The original has no tweeter protection (Polyswitch), while the second revised schematic does.
In previous Polk designs, the Polyswitch is the first component in the high pass circuit.
When its rating is exceeded, the Polyswitch opens, and the tweeter is disconnected.
On the revised schematic, the Polyswitch is in the middle, shunted by a 4.2uf Capacitor.
Best guess, when the Polyswitch trips, the signal is routed through the 4.2uf cap, which when added to the 12uf down stream, equals a total capacitance of approximately 3.1uf.
This raises the crossover point dramatically, preventing excessive voice coil movement, thereby saving the tweeter ( in theory ).
You cannot replace the Polyswitch in the revised design with a .5 ohm resistor.
You have two choices, eliminate the Polyswitch and Shunt Cap altogether, or replace the Polyswitch and Shunt Cap with a new ones ( http://www.digikey.com/product-detail/en/te-connectivity-raychem-circuit-protection/RXE090/RXE090-ND/5788 ).


Just realized the original post is 3 years old.............

JS1961

Thanks for the prompt response, and insight into the design differences between the original Monitor 10 series, and the Monitor 12 Series 2. I've since wired mine parallel/series (top /bottom).

[Deleted User]

To answer this old question, the harness out of my Monitor 12 s2 is not like the drawing. It parallels the two bottom woofers and parallels the two uppers, then wires the two groups in series. The crossovers were version 2 with poly switches.

As for the jumper circled in red, everything I've learned and practiced the past 40 years says it shouldn't be there. I asked an engineer way smarter than any of us to look at this and he says it isn't something he'd do. In the end Polk didn't actually wire my M12's that way either. I've since built new crossovers and rewired everything completely eliminating all OEM parts. Also separated woofer and tweeter inputs with 4 Cardas posts and made a couple of changes to the crossovers. The one thing I didn't do was separate the woofers into two pairs and cross one pair over lower. I think all woofers playing so high is a mistake. Two playing up to the tweeters should be plenty and make them easier to listen to at loud volumes for any amount of time. My Carver pre-amp has a mid adjuster luckily for me to back the bark down a little.