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I auditioned some components at a few local shops and got the chance to listen to the Polk MM series. I fell in love with them and the price is attractive enough to have me really think about using them so here's where I'm at. The MM components are rated at 2.7ohms so the question is if I run the components active, will each channel (4-channel amp) still see 2.7ohms?

I have a Polk PA660 that is rated at 75x4 at 4ohm that I would like to keep and I'm wondering whether to go active and run each mid and tweet on their own channels, or bridge the amp and run them passive. I really don't know that the amp would appreciate running 2.7ohms bridged.
 

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I have a set of MM6501 running active on a JL XD400/4 and it sounds awesome. I also have an Alpine H660 Imprint processor feeding the 2 amps I'm running. Does not answer your question, but is a little relevant.

Check the OHM's with a DMM, to see what they read without the crossover.
If it stops raining here I'll go see what mine read.
 

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if they are rated for 2.7 (3) ohms, then that is almost always the rating of the drivers themselves and not with the crossover. if you run it active, it will see a nominal 2.7(3) ohms.
 

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the impedance won't change
Impedance is by definition frequency dependant. Using the cross over, at low frequencies the amp sees the impedance of the mid/woofer and at high frequencies it sees the impedance of the tweeter.

Measuring the impedance with a DC DMM is just giving a nominal impedance. Its really only measuring resistance of the Voice coil. If you measure the DC resistance at the input of a crossover that is connected to mids/tweets you are basically measuring the resistance of the LF inductor in series with the Mid/woofer as the tweeter has a cap in series and is an open circuit at DC
 

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I believe that the nominal impedance of the woofer is 2 ohms and the tweeter is 4 ohms. I currently have these in my car, but they are running off of the passives. I have yet to check them with my DMM, but I will do it just to confirm next time I get a chance.

I also have to say that the Polk MM 6501's are nice sounding speakers and I have been pretty pleased with them. Up until a week ago i had been running the Polks off of the mostly anemic factory amplifier.

I was never even close to being satisfied with the sound so over the holiday's I purchased an AudioControl, LCQ-1 OEM integration device from Crutchfield and an Audio System, Twister F4 380 amplifier from another member to start completing my system. I have to say that as soon as I amplified them they have really came to life and impressed me. I feel like the real superstar of the set is the mid and I sometimes feel that the tweeter is just missing a little something. That being said, I previously ordered a set of Focal 165 V30's and I am going to put them head to head as soon as i get a chance. I was able to demo them and I really liked the way they sounded on the board.
 
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