Mackie SRM450 v1 interesting tweeter polarity confusion.

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Hi all ... I've replaced tweeter diaphragms on a good few of these and always followed the normal wiring polarity coding of Blue/Black stripe to tweeter negative terminal.

But after carrying out a repair to the amp on one I have here now I noticed on the schematic that connecting this way effectively reverses the tweeter polarity with respect to the woofer ...

The schematic diagram connection at the square 4 pin molex on the PCB is polarity reversed in a physically impossible way from the J16 pins 1&2 (male socket on the PCB) to the J1 pins 2&1 (female connecting plug) connection wires for the tweeter.

Because of the original wiring never having been changed and the impossibility of plugging the molex in the wrong way round, I thought I'd just confirm with a local Mackie service centre that the reverse polarity was intentional.

But it seems they think it is incorrect ... here is the reply after it being discussed at their service centre:

"One of the tweeter connections should be grounded at the amp end, so that would be easy to check with a meter. I can’t see anything in the Service Manual to suggest that the tweeter should be connected out of phase, so I would just connect the terminal that is ground to the -ve of the tweeter."

The J16 socket connector on the PCB matches the correct polarity output from the amp ... but obviously you CANNOT physically cross connections on a square 4 pin molex ...

So the HF OUT+ on pin1 of the socket on the PCB (J16-1) ... carries straight across to the associated pin1 of the plug to the tweeter (J1-1) meaning that HF OUT+ is now on the Blue/Black stripe wire & if this is connected to the tweeter negative terminal it is out of phase with the woofer. The Mackie service tech. is telling me he would connect the Blue/Black stripe wire to the positive terminal on the tweeter for correct polarity?

I have written back asking for further clarification as if the reverse polarity is unintentional then me and LOT'S of other people have been connecting these tweeters the wrong way round for a LOOONG time now.

See attached focused screen cap of the associated part of the schematic ... anybody else ever notice this or found tweeter connecting wires the other way round?

[x-pro]

Is the correct polarity that important to you? Can you hear the difference for a tweeter?
No human being can hear the difference. Only instruments can.

[Helmholtz]

There's a possibility that either the crossover or the tweeter amp reverses phase.
Apart from that I think that phase relation between woofer and tweeter only matters in the overlap region around the crossover frequency.
I case of doubt just reverse the tweeter wires and listen to some recording for a difference.

[g1]

I've seen other manufacturers have woofer and tweeter of different polarity. It depends on what is going on in the crossover (or other active circuitry).
Here is an example with tweet + connected to woofer -

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Is the correct polarity that important to you? Can you hear the difference for a tweeter?
No human being can hear the difference. Only instruments can.

Well no it's not that important to me but I would like to know the way it was designed to be orientated along with the crossover originally.

It's not a matter of life or death LOL ... just wondered if anybody else had noticed the impossible molex connection on the schematic?

I found it interesting as I & everybody else I've seen have been connecting them the obvious way for so long ... when the schematic shows them to be connected the other way round ... with a pinout numbering and wire code mistake ...

[g1]

just wondered if anybody else had noticed the impossible molex connection on the schematic?

We can't see what you mean from the image you posted.

[Check.. 1,2]

I've seen other manufacturers have woofer and tweeter of different polarity. It depends on what is going on in the crossover (or other active circuitry).
Here is an example with tweet + connected to woofer -

Me too ... I was just interested in the original intended polarity and found it amusing that litterally everybody may be wiring these the opposite way round to the way that it was intended in the original design whether that makes a difference to the sound or not ...

[Check.. 1,2]

We can't see what you mean from the image you posted.

It's impossible for J16-1 to pass signal to J1-2 ...

[g1]

That could just be a typo. What I meant was we can't see where the molex pin labelled J16-1 on that drawing is physically going to. You would want to do resistance checks and determine whether there is a typo on that diagram, or if the blue wire to tweet actually ends up going to circuit board ground.

[Check.. 1,2]

That could just be a typo. What I meant was we can't see where the molex pin labelled J16-1 on that drawing is physically going to. You would want to do resistance checks and determine whether there is a typo on that diagram, or if the blue wire to tweet actually ends up going to circuit board ground.

The pinout on J16 are all correct label & polarity (tested electronically) ... that still doesn't make it possible to connect J16-1 to J1-2 through the square molex .... in reality Pin 1 on the output socket joins to Pin 1 on the plug going to the tweeter J16-2 is the ground therefore J1-2 is the ground ...

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Here's more schematic as requested:

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Here's the speaker connections again full size so you can see the two schematics together :

[The Dude]

Is the correct polarity that important to you? Can you hear the difference for a tweeter?
No human being can hear the difference. Only instruments can.

I disagree. If you only had one speaker, you wouldn't notice because there's nothing for those frequencies to be out of phase with. However, if you were running pairs or multiple speakers, you'd certainly notice. Some manufacturers intentionally wire the tweeter out of phase with the woofer so that there isn't a bump at the crossover frequency. And, as has been stated, it could be that the amp flips phase and reverse wiring the horn driver corrects it. Only Mackie knows what was intended. Either way, if you just wire the replacement diaphragm the same as it came from the factory, I should think that it would match all other factory speakers that are out in the world. When I unhook a diaphragm or speaker for repair or replacement, I just tie a loose knot in the wire that went to the positive terminal. Then, when parts or replacements come in, I know exactly how it was originally wired.

[Check.. 1,2]

Only Mackie knows what was intended. Either way, if you just wire the replacement diaphragm the same as it came from the factory, I should think that it would match all other factory speakers that are out in the world.

The out of phase wiring is the original orientation and the way I've always done it ... but the schematic and the local Mackie service centre here seem to disagree and say that it should be in phase & that is the way he would connect it.

It would be amusing though if every SRM owner in the world had been wiring their tweeters in opposite phase to what the original designer intended ... some will say it makes no difference, some will say it makes a big difference ... some will swear blind it will make their car fuel consumption better ...

I was trying to avoid a phase debate ... just interested if anybody else had noticed in all the years they've been out and would just like to know what the intended original orientation was ...

[J M Fahey]

You canīt hear absolute phase but as mentioned above, *two* speakers working at the same frequency will add/substract, big time, producing a bump or a notch.
Pick your poison but results are definitely audible or visible on a graph.

As of the apparent "polarity inversion", typically woofer will be in series with an inductor, tweeter with a capacitor, which advance or delay phase.
At the exact crossover frequency *both* will be so much out of whack that often inverting one takes them closer, go figure.