M&K subwoofer Push-Pull Polarity Question

[mcleanmb]

I am replacing the plate amplifier in my old MX-100 dual 12 push-pull subwoofer. I am in the final stage of replacement. I cannot seem to get an answer on the polarity of the 2 12-inch drivers. One fires forward externally, and one fires up internally from the bottom of the cabinet. Sealed enclosure.

Both speakers were connected separately, but directly, to the old amplifier. Old amp on the left in the picture, new amp on the right. The speakers came out of the plug right by the MX-100 sticker. That's the model number of the subwoofer.

As can be seen, the front-firing speaker is wired using normal polarity, and the upward-firing speaker in the bottom appears to be as well. But, I've heard many people saying one of the two speakers needs to have the polarity reversed. I'm thinking that's inaccurate, but I need a final answer before reassembling. By the way, I did contact Ken Kreisel, the designer of the subwoofer, and he was very responsive. I've just not heard back on this final question so figured I would ask around! He also recommended the replacement amplifier on the right side of the picture.

Also, since the new amplifier only has one speaker output, should I wire these in series? Parallel? Or some other way? I'm somewhat of a newbie so I apologize if this is not a super-bright question. That was not an audiophile pun.

Anyone out there with any knowledge? Would be greatly appreciated!

 

[Sonnie]

I would hold off and wait on Ken for this. I'm not sure how many folks out there have swapped these amps with the new amp being different. Maybe I'm living under a rock on this, but I'd be surprised if you found the correct answer outside of Ken.

 

[VJM]

I have a MX-105 MKII and also have the upgraded Super Fast Drivers before the original MK went out of business. I recall discussing this with them, they said the bottom driver is polarity reversed even though the cables still show red for positive and black for negative, it's designed this way from the amp (reversed polarity at the amp).
This is done so both drivers are pushing out and in the same relative to the outside of the subwoofer, i.e. when the driver on the front is pushing out the bottom driver is also pushing out, hopefully that makes sense.
I think if the bottom driver polarity is not reversed they will cancel each other out and the output will be more quiet.

 

[mcleanmb]

I have a MX-105 MKII and also have the upgraded Super Fast Drivers before the original MK went out of business. I recall discussing this with them, they said the bottom driver is polarity reversed even though the cables still show red for positive and black for negative, it's designed this way from the amp (reversed polarity at the amp).
This is done so both drivers are pushing out and in the same relative to the outside of the subwoofer, i.e. when the driver on the front is pushing out the bottom driver is also pushing out, hopefully that makes sense.
I think if the bottom driver polarity is not reversed they will cancel each other out and the output will be more quiet.

Yeah, 50% of people say reverse the polarity and 50% say normal polarity. I have an MX-200 as well, but same thing, it's wired directly to the circuit board. I wish the circuit board was labeled! Maybe I will try to crank it up and see if I can tell if the woofers are moving in opposite directions or not. What I really need to do is get in touch with Ken Kreisel again. I guess that will be the final answer! The cables going to the up-firing woofer are red and black, but they are striped. I'm wondering if striped actually means reversed polarity?

 

[Tim Hector]

Under normal circumstances, both should be in the same polarity. This is not opinion, fact. 2 woofers firing in the same direction cuts vas. Are you experimenting with vas or room cancelation? When you play, it'll be obvious from the bass output.

 

[Tim Hector]

Ah, I just read the other post, sorry my post above I just answered without reading the others. So, it is possible to have a a driver (transister-not speaker) or amp designed that is out of phase. Conrad Johnson comes to mind, it was a regular part of their designs. If that is the case, it is possible to need to reverse phase on the woofer.

 

[mcleanmb]

Yes, I finally did get the response from Ken Kreisel. Here is a cut-and-paste of his response about the polarity of the two drivers: "Matt, the bottom woofer gets wired electrically out-of-phase with the front driver so that both woofer drivers are mechanically in-phase (both cones go out together and in together). If you are using the original wiring, the drivers might already be wired electrically out-of-phase. It will not hurt anything if you have wired the two drivers electrically in-phase, but you will get relatively little bass."

So, I guess my next question would be: since both drivers were independently wired to the original amplifier, and the new amplifier only has one mono speaker output, would I just wire them in parallel to the front-firing woofer first with normal polarity, and then reverse the polarity going to the bottom up-firing woofer? I am a novice, so sorry that some of these questions are super naïve.