Monitor 10B "nominal" impedence?

avguytx

After reading a post in another forum this morning about what his speakers were reading, I decided to check mine with a DMM, too. One reads 3.0 ohms and the other is 4.7 ohms! What is the "rated" nominal impedence on the Monitor 10B's? They both sound fine but that kind of worries me. When I push in on the PR, there is no scratchy sound from the voice coil. I guess the next step is to pull the drivers and write down what each of them are reading independently. Could be a shorted driver and/or a bad crossover component. Oh well. Something to do after I get back from CES! lol

Oh, and I even put fresh batteries in my DMM just to make sure that wasn't it! lol

seo

Does measuring with a DMM replicate the full frequency range correctly? I;m not sure you can measure it that way, but I am interested to hear what more experienced folks have to say.

WilliamM2

I don't know if it's an accurate way to measure it or not, but I would still think both speakers should have the same reading.

avguytx

Well, I did some more research on these 10B's. I pulled the drivers out of the cabinets and found out some interesting things. One cabinet has 2) MM6502's that are 4-ohm drivers (metered at 3.6 and 3.7 ohms) and an SL2000 tweeter that metered 6.8 ohm that apparently was replaced because it had a DOM of June 1990. The mids were made in May 1985. This cabinet meters at 2.7 ohm with all drivers in.

The other cabinet (this is where it gets interesting) has 2) MM6502's that meter 8 ohm (6.9 and 7.2 ohm) and an SL2000 tweeter that meters at 7.2 ohm (8 ohm basically). All of the drivers were dated in January 1985. This cabinet measures 4.3 ohm which makes sense with the mids being what they are.

The serial numbers are 134207 and 132914 and both say Monitor 10B on the terminal cup, so they aren't far apart, really. So now I wonder which mids are supposed to be in there. 4-ohm wired in series to 8-ohm (which makes sense) or 8-ohm drivers which would make for 4-ohm in parallel.

So this baffles me. I just want to have the right drivers in them and make sure my Carver M1.0t sees the right impedance! I know it'
s stable to 4-ohm but still. I measured other speakers I have (about 12 pairs) and the ones rated at 8-ohm nominally meter where they should around 6.5 to 7.3 ohm or so. The 4-ohm ones are between 3.5 and 4.2 ohms.

What do you guys think?

ben62670

As far as i can tell all monitor 10's were wired parallel.
The 10b's should have either 6501's or 6503's
your crossover points must be off by quite a bit.
heres a link for wiring, and parts used by Polk

http://clubpolk.polkaudio.com/service/models/modelpartslist.php3?model=monitor

http://www.polkaudio.com/forums/showthread.php?t=38755

I would definetly change out those speakers. The old monitor 10's had mw6500's so that could be a viable options too.

Good luck with your new project Ben

avguytx

ben62670 wrote:

As far as i can tell all monitor 10's were wired parallel.
The 10b's should have either 6501's or 6503's
your crossover points must be off by quite a bit.
heres a link for wiring, and parts used by Polk
I would definetly change out those speakers. The old monitor 10's had mw6500's so that could be a viable options too.

Good luck with your new project Ben

I was talking with Ken at Polk today and he seemed a little baffled about it too. My 10B's have miss-matched pairs of MM6502's and, from the schematic and the other chart, they should have the MM6503's. Great. I have the right original tweeters even though one was swapped out in 1990 by whoever had them then. I'll do the mids first most likely and the tweeters will be last...after the crossover upgrade too.

But for now, I'll listen to them like they are! lol

ben62670

Little note the woofers are MW as in mid woofer. I had some mw6502's where there were supposed to be mw6503's. Just wait till you get the proper drivers in there.

Enjoy
Ben

avguytx

So you're saying it will be even better huh? Which Polk's were they in that you had/have? I think I'll do the woofer swap first and the crossover rebuild. Might do the tweeters later on.

ben62670

I have had all sorts of vintage polks. monitor10 monitor 4.6's monitor 5's RTa15's SDA2's, and now building sda-srs

heiney9

Most of the original MW's are not available anymore. There is one model MW they still sell which can be used universally in all the vintage Polks; however it's not the exact spec for all replacements, but it's close enough that you probably would never hear a difference.

H9

dkg999

Monitor 10B's with the right mid/woof drivers, the SL2000's replaced with the RD tweeter, driven by a tube pre and decent SS amp, are scary good!

avguytx

heiney9 wrote:

Most of the original MW's are not available anymore. There is one model MW they still sell which can be used universally in all the vintage Polks; however it's not the exact spec for all replacements, but it's close enough that you probably would never hear a difference.

H9

Ken just emailed me awhile ago saying they still have MW6503's for $48 each...same price as the tweeters!

heiney9

avguytx wrote:

Ken just emailed me awhile ago saying they still have MW6503's for $48 each...same price as the tweeters!

Cool you're good to go. Ken and Polk CS are the best in the business...bar none.

Refefer

+1 to that!

Polk CS has been there every time I needed them... and part of what kept me as a customer.

Nothing is worst than a customer service who doesn't care.