Polarity determination

[mfaz28]

Now that I've replaced my mid's. I'm wondering if there's a definitive way to establish correct polarity. Not only for the mid's but tweet's as well....Might as well be sure??

[Carlspeak]

What's your AR model?

[ra.ra]

Assuming you are still discussing the 2ax model as in previous thread, these are the two best schematics I've kept filed away. Yellow wire connects from 'B' on pot to positive terminal on driver (yellow dot); the other driver terminal wire connects to "2" on pot, and then continues to "T" on rear speaker terminal.

Two things I cannot explain but please note: in these two schematics, there is a difference in coil value; also, the 209XXX pair shows an additional resistor in the midrange circuit.

[mfaz28]

AR2Ax. Yes...Confusing that my admitadly limited research has yielded different configurations on apparently factory soldiered connections as to where the yellow mid wire goes, leading to my questions about total polarity.....Note 2ax schematic does not show yellow dot orientation on the driver...

[ra.ra]

Uh-oh, this requires a better explanation than I can offer. The attached threads suggest that the yellow dot on the HF drivers represents the negative terminal, whereas I've always thought that the painted dot on old AR drivers was consistently identified with positive.

Regarding schematics attached above, if yellow dot is negative, the lower schematic suggests all drivers with similar polarity. Conversely, the upper schematic (with no paint dots indicated) shows the mid and tweet with dissimilar polarity from woofer. Did the polarity wiring of the mid/tweet drivers change between the early and late 2ax versions? It is suggested in one of these threads that the change between "old" and "new" occurred somewhere around s/n 125,000, which does fall between the serial numbers in the schematics shown.

There are a ton of 2ax's out there, so I suspect someone with more extensive familiarity can explain this succinctly. 

 

[RoyC]

I have checked the polarity of a few 2ax mids, and the yellow dot has been on  the + terminal side each time...which connects to the yellow crossover wire as shown in the schematics above.

Other items of interest:

-The #5 coil was replaced with the #7 coil about the time the early foam surround woofer (having the wide flange of the cloth surround woofer) was replaced with the standard size woofer in 1970. This is the primary reason for the woofer to mid crossover point change.

-The reason the tweeter crossover specs changed form 7500 to 5000 is the DCR of the early tweeter is crazy low (below 2 ohms). Even though the crossover tweeter capacitor stayed the same (4uf), the low resistance of the early tweeter resulted in a higher electrical crossover frequency. The higher resistance of the later tweeter resulted in a lower crossover point.

-The later (last) 2ax mid used in the last batch of 2ax's had a higher DCR of 9 ohms vs 6 ohms for the earlier mid. They look identical, so it is prudent to measure the resistance of replacement mids. The mid with the higher dcr was used with the last 2ax woofer, having a square ferrite magnet (around 1974-75).

Roy

 

[ra.ra]

Thanks, Roy, for outlining several factors contributing to the different components and specs for the various iterations of the 2ax's evolution. Just to be clear - - to the OP's question - - is it correct to say that all versions of the 2ax had the same wiring configuration with regards to polarity: mid and tweet positive tabs connect to #1 speaker terminal (-); while woofer positive tab connects to #2 speaker terminal (+) ? This would confirm the validity of the schematics shown above with dissimilar polarity.

What really threw me off was reading a thread from 2008 concerning an AR-2a to 2ax conversion where that OP was trying to figure out the wiring and component values - - - one excerpt shown below.  

[RoyC]

Based on some anecdotal testing evidence and conversations with some compatriots, the assumption at the time was that the 2ax mid was the exception to the rule, and the yellow dot was actually on the - side. The bottom line is we really don't know what AR was doing with voice coil polarity along the way. It is best to simply follow the schematics you posted...and where the original wiring is still present, just connect the yellow wire to the mid's yellow dot.

Recent testing suggests that the early tweeter appears to be connected with like-polarity to that of the woofer, yet the later tweeter, with wires crossed under the electrical tape, does not. To complicate matters even more, the polarity of the early tweeter's voice coil was allegedly changed at one point to be used with an iteration of the AR-3. Fortunately, the sonic impact of differences in original 2ax tweeter polarity are very subtle.

Roy

[ra.ra]

.....and I had thought this model was fairly straightforward, whereas it seems the number of permutations and tweaks, both large and small, is indeed rather complicated, if not slightly amusing.  Compounding my curiosity was when I began to consider how this 2ax mid is used as the AR-4 tweeter [which is (+) to (+) for both drivers]. Thx again, Roy, to you and others who conduct this research, and then amass and share all of this helpful data.

[RoyC]

I remember a post by Ken Kantor stating there was little uniformity in terms of voice coil installation in AR woofers in the early days, and that polarity was determined after manufacture. This would explain why we find the location of + and - to vary on woofers. Add this to inconsistent or absent labeling of terminals, yellow dots, fiberglass covered midrange drivers, mid -stream crossover changes, etc, and the polarity issue becomes a real headache.

Another puzzle has been the crossing of AR-5 and AR-3a midrange front-wired leads on some early iterations of these models. Is it because the voice coil installation was reversed compared to later versions of the mids, or did AR deliberately reverse the polarity of these mids compared to later 5's and 3a's? Based on a couple of tests, I believe some of the early dome mids' voice coil installations were reversed, meaning proper polarity was maintained by crossing the surface leads of these mids. If, however, someone uses one of these mids as a replacement in the much more common later version, there is a good chance the polarity will be incorrect if the person doesn't know to cross the leads....and, once again, these mids are inconsistently labeled. Sigh...

Roy

[mfaz28]

Roy.....Thanks....Is there ANY way to sort this out....??

[RoyC]

16 hours ago, mfaz28 said:

Roy.....Thanks....Is there ANY way to sort this out....??

If you are curious, remove the screen and fiberglass pad from your mids and check the polarity. Otherwise, assuming your mids have a yellow dot next to one terminal, just follow the schematics above. What exactly are you trying to sort out?

Roy

[Dchristie]

I am restoring an early pair of AR 2ax speakers (cloth woofer and serial numbers both of both speakers in the 50 k range) and noticed this polarity discussion .

Both the screens of the paper cone mid/tweets for my speakers easily popped of due to aging glue so I was able to directly check for polarity using the  battery test. However, on both of the cone mid/tweeters from this pair of speakers the light green wired terminal tested positive not the yellow dot terminal. I  checked several times just to be sure . The phenolic tweeter  lead that was wired to the yellow wired terminal as per the schematics did test positive via the battery test so it was the same as the schematic.

Is it possible that these were wrongly wired from the factory ? Pretty sure the speakers have not been rewired prior to my possession as the grill was impossible to get off (lots of nails and glue). Not knowing for sure, but I can envision the frames of the drivers being prepainted at the factory with the yellow dot for easy hook-up (yellow wire to yellow dot ) by a line assembler and maybe the wire cross-up occurred (and was missed) in the original assembly of the driver itself. I had a pair of LSTs come to me wired out of phase (bass drivers reversed ) so I know that accidents do happen.

So, my speakers had the bass and super tweeter wired in phase ( positive to positive) but the mid/tweeter wired out of phase to the others ( positive to negative) and now, I am thinking that I should rewire the drivers according to the schematics presented on these sites (positive lead from pot going to to the positive terminal of the mid/tweeter which originally had the light green wire attached ) and not to the yellow dot negative terminal.

 

Dean

[Dchristie]

Rechecked all my drivers and here is finally what I have for this early model AR 2ax.

cloth surround woofer - wired in phase with positive input through inductor to positive woofer terminal and negative input to negative terminal

cone mid - wired in phase with negative input through cap to negative terminal on mid ( yellow wire to yellow dot marking which is the negative input on this particular pair of mids ) and positive input to positive terminal

phenolic dome tweeter - wired out of phase with negative input through cap to tweeter positive terminal ( yellow wire to tweeter +) and positive input to negative tweeter terminal

So, only the tweeter is wired out of phase in this speaker pair.

Wondering if this makes sense since the speaker is only using 1st order crossovers to the drivers so why the inverted polarity on the tweeter. This also varies from some of the other crossovers for this speaker as they have both the mid cone and tweeter dome  inverted compared to the bass driver.

I am tempted to just wire all drivers in phase but still keep the mid and tweeter caps in the negative legs and the woofer inductor in  the positive leg but then again, maybe it is best to just follow what was done originally in these speakers?

Any comments are welcomed! 

[Dchristie]

Realized I made a mistake with my woofer comment above , it is wired in phase ( + to + and - to -) , but the inductor is in the negative leg - not the positive leg of the crossover (wired similar to the mid cone). And maybe I should be using the terms normal and reverse polarity instead of in or out of phase in this case. 

[RoyC]

44 minutes ago, Dchristie said:

 

I would be much more concerned if the mids were wired differently or opposite of each other. Despite variations in voice coil installation and labeling of drivers (usually early woofers), it is very rare to find an improperly wired AR speaker. I believe the best rule of thumb is to stay with the original wiring (yellow wire to yellow dot, as found in your specimens), and not to overthink it.

Another thought...Given the variable state of the original tweeters, it could be interesting to experiment with the mids' polarity, and simply going with what sounds best. 

Roy

 

[Dchristie]

Thanks Roy.

I think that I will do just that and go with the original wiring for this pair of speakers (mid wired with normal polarity.) But, I will do some reversing just to see (or hear) what changes since some schematics show it reversed. Problem is that it seems that unless you remove the protective screen and visibly test each mid cone you never really know what polarity the yellow dot indicates. Until I tested mine, I assumed the yellow dot was positive terminal which ended up being not so. You have also found them to be on the + terminal side but also had some compatriots who indicated that it was on the - side ( like mine) .  

I will also play around with the tweeter wiring as well - just to see how it sounds when wired with normal polarity and reversed as per my speakers. It adds so little to the whole picture however,  it might prove difficult to hear any changes in polarity .

Dean

[RoyC]

8 hours ago, Dchristie said:

Thanks Roy.

I think that I will do just that and go with the original wiring for this pair of speakers (mid wired with normal polarity.) But, I will do some reversing just to see (or hear) what changes since some schematics show it reversed. Problem is that it seems that unless you remove the protective screen and visibly test each mid cone you never really know what polarity the yellow dot indicates.

Dean

Your 2ax's do jive with other accounts I've heard about, so I'm sure they are OK, Dean. The two mids I measured were in a box of parts, and very well could be the exception. In retrospect, given the similarities, they could have been from earlier AR models equipped with the fiberglass covered cone driver.  It is also entirely possible folks drawing 2ax schematics just assumed the yellow dot represented the positive side of the driver. Though it would be interesting to know for sure, I honestly don't see it as a problem.  In my opinion routinely prying the grills off the mids as part of a 2ax restoration is unnecessary and potentially damaging. AR conveniently placed a yellow dot where the yellow wire should go.

Roy