Monitor 7B Repairs

emaraszek

Hi everyone, new member here with a pair of Monitor 7Bs I just acquired. I plan on keeping the original Peerless tweeters installed, but I need to address the damaged mids and passives (see pictures). After reading through some of the other threads here, it looks like these need to be replaced rather than being repaired. I just want to confirm a few details so that I get it right.







I found a replacement pair of passives on eBay that I just scooped up, so that should take care of that issue. For the mids, it looks like the MW6502 is supposed to be the correct replacement, but I'm not sure in this case. Mine say "Monitor Series Driver MW6500" so I'm not sure if they were just labeled that way at one point or if I need to be looking for a different model.

Thanks in advance!

pitdogg2

It would be best to replace with more mw6500. Search ebay and save the search. You'll be notified by email that some are on ebay bid accordingly.

emaraszek

Thanks @pitdogg2, so these MW6500s are actually a different model than the MW6502 then. Any recommendations for a compatible replacement? Should I call Polk? I don't see any MW6500s on eBay, etc. - not even clones.

F1nut

Polk doesn't have any.

emaraszek

Hmm ok, what about swapping to MW6503s instead? Or could I even switch out/modify the crossovers so that I can use MW6502s? Seems to be a lot more of those available

Gardenstater

MW6500 do come up often enough. Seems to be a lull right now, due to ones selling recently, like these: https://www.ebay.com/itm/MATCHED-PAIR-of-Polk-Audio-MW6500-6-5-Woofers-For-Monitor-Series-/184279462575?ul_noapp=true&nma=true&si=%2Fz9f7kJJp3oWOLHmUZZO17vQyis%3D&orig_cvip=true&nordt=true&rt=nc&_trksid=p2047675.l2557

Gardenstater

MW6502 would be an unacceptable replacement in my opinion, due to the nominal impedances being different from the MW6500. This thread has the thiel small parameters: https://forum.polkaudio.com/discussion/133992/thiele-small-parameters-for-mw6500-drivers

emaraszek

Yeah the 4 ohm MW6502 is definitely not a drop-in replacement for the 8 ohm MW6500. I was more wondering whether it would be a good plan to swap to crossovers from a later model that came with the MW6502. I believe there were 7s that came with the Peerless tweeter and the 4 ohm mid, so theoretically such a crossover would exist. Only wondering because I see a lot of MW6502s available at the moment and crossovers seem to be going for pretty cheap.

F1nut

Dude, just wait for the proper drivers.

Gardenstater

Your 7B's appear to be of 1981 vintage whereas mine are 1979. Do you have the following crossover which doesn't appear in this forum in the archives for some mysterious reason? I don't know why the later Model 7's did use the MW6502, with very little change in crossovers, except for less resistance in the tweeter circuit. It MUST have something to do with the tweeters not being the Peerless in the later models. I would not change anything unless you also want to swap out to the crappier tweeters that Polk used in the later models as well lol.

Gardenstater

I guess it would be nice to know *if* there really was a Model 7 that was made by Polk that combined an MW6502 with a Peerless tweeter. If there was remember that there were also Peerless Tweeters that were 4 Ohm models rather than 8 Ohm, but I do not know if Polk used them. It's unfortunate that our schematics seem to be incomplete AND the earliest schematic in the archive here is dated 1984 and although it shows an MW6502, it unfortunately fails to identify the tweeter.

emaraszek

@Gardenstater Thanks for posting that schematic. It does seem to represent the crossovers that I have in my 7Bs. I have a 4.5 ohm in place of the 4.7 ohm resistor though, and the caps are tough to identify since they all seem to have been soldered in with the markings facing down... (I can just barely make out a "34" on the one, and have to assume the other is a 12)



I looked at the other M7 schematics in the archive too. The 1984 file you mentioned is identical to the 1989 file, which identifies the tweeter as an SL2000. Since the SL2000 is an 8 ohm and my Peerless tweeters are also 8 ohm, the Peerless tweeters should theoretically work just fine with the newer crossover and MW6502 mids. In fact, I was planning on doing the resistor/cap replacement anyway, so I could even just remove the 2.7 ohm at that point and replace the 4.5 with a 2 ohm that the newer crossovers have.

Any reason (in theory) that this wouldn't work? I'm willing to do a little experimenting.

Gardenstater

My crossovers also have a 4.5 Ohm instead of the 4.7 Ohm in that schematic I posted, which was offered to me by another member and I don't know the origin of it. I'll give some more thought to your other comments. I was told that the SL1000 tweeter was the one that Polk shipped the customers as a warranty replacement for the Peerless. There's more to a tweeter than just the nominal impedance and the best blending between the midbass drivers and the tweeters is derived by experimentation and listening and measurements. Impedance varies greatly across a tweeter's operational range.

Gardenstater

I would keep the MW6500s even if it means you have to wait for one. Definitely I would keep the Peerless's. Here's what the crossover will look like if you use the same components I did:

emaraszek

Update: new PRs are in, still looking for some MW6500s.



Also need another Peerless tweeter as 1 is blown At this point I'm back to wondering if it makes more sense to just swap crossovers and pick up some MW6502s and a couple RDO194s, especially since I need to replace all but one functional tweeter...

What do you guys think? Is the Peerless/MW6500 setup superior to the RDO194/MW6502 setup or is it the other way around?

vulcan

I would try and find original replacement drivers and tweeters. Keep checking Ebay.

Gardenstater

Other places to look are Craigslist and FB Marketplace. Sometimes you might find a great deal on whole speakers that is less than the price of the components you need.

emaraszek

@Gardenstater I'm seriously considering that $50 pair of 10s you posted about (https://forum.polkaudio.com/discussion/comment/2594309/#Comment_2594309)

I also added a link to a couple older 10s with what I believe are the silver basket MW6500s, in case anyone is looking for those (https://forum.polkaudio.com/discussion/comment/2594424/#Comment_2594424)

Gardenstater

Well you might want to be careful there because I think they used MW6501 in the earlier 10s and then MW6503 in the later ones. I don't know if they ever used MW6500s. The cabinet volume is greater in the 10 vs the 7 and that might've meant it needed a different driver, not to mention that there were two of them vs one.

emaraszek

Waiting to hear back from the seller on what model they are. It would be a long drive to get them, but potentially worth it

Faustin

Gardenstater wrote: »

Well you might want to be careful there because I think they used MW6501 in the earlier 10s and then MW6503 in the later ones. I don't know if they ever used MW6500s. The cabinet volume is greater in the 10 vs the 7 and that might've meant it needed a different driver, not to mention that there were two of them vs one.

I have a pair of 10's, circa 1979 that I bought new that have silver basket MW6500 drivers. The MW6500 was used quiye a bit early on in the 10's and 7's.

Gardenstater

Thanks good to know. Once again it seems our archive of schematics is totally missing coverage of those earlier models. I couldn't find a schematic that matched my early 7Bs (1979) either, which have silver basket MW6500s.

@Faustin Does your circa 1979 pair of 10's have a different crossover than the earliest schematic here in the archives? My 7B's did.

F1nut

The schematics that are posted are all that was available, so what's missing will stay missing.

Faustin

@Gardenstater - my 10 c/o is the same as the original schematic......except it has the MW6500 drivers.

Gardenstater

Thanks Faustin. That's interesting that Polk went from MW6500 to MW6501 without making any changes whatsoever to the crossover. Here's the thiele parameters of some of the drivers. H/T westmassguy:

Got these from various sources, including Club Polk, props to the original posters:

Driver: MW 6500 Driver's model #.
Brand: Polk Driver's brand name.
Fs: 31.0000 Hz (Free air resonance)
Vas: 2.6486 ft^3 (Compliance volume)
Qts: 0.2190 Total Q
Qms: 1.3000 Mechanical Q
Qes: 0.2640 Electrical Q
Sd: 0.0130 M^2 (Piston area)
Xmax: 3.1800 mm (Cone excursion, linear)
Revc: 6.5000 ohms (DC resistance)
Znom: 8.0000 ohms (Nominal impedance)
Pmax: 35.0000 watts maximum rated power


Driver: MW 6501 Driver's model #.
Brand: Polk Driver's brand name.
Fs: 31.0000 Hz (Free air resonance)
Vas: 2.7545 ft^3 (Compliance volume)
Qts: 0.2790 Total Q
Qms: 1.4700 Mechanical Q
Qes: 0.3440 Electrical Q
Sd: 0.0130 M^2 (Piston area)
Xmax: 3.1800 mm (Cone excursion, linear)
Revc: 7.7500 ohms (DC resistance)
Znom: 8.0000 ohms (Nominal impedance)
Pmax: 35.0000 watts maximum rated power


Driver: MW 6502 Driver's model #.
Brand: Polk Driver's brand name.
Fs: 44.0000 Hz (Free air resonance)
Vas: 1.2360 ft^3 (Compliance volume)
Qts: 0.2790 Total Q
Qms: 1.9700 Mechanical Q
Qes: 0.3250 Electrical Q
Sd: 0.0130 M^2 (Piston area)
Xmax: 3.1800 mm (Cone excursion, linear)
Revc: 3.5200 ohms (DC resistance)
Znom: 4.0000 ohms (Nominal impedance)
Pmax: 35.0000 watts maximum rated power


Driver: MW 6503 Driver's model #.
Brand: Polk Driver's brand name.
Fs: 29.8600 Hz (Free air resonance)
Vas: 3.0017 ft^3 (Compliance volume)
Qts: 0.3100 Total Q
Qms: 1.7680 Mechanical Q
Qes: 0.3760 Electrical Q
Sd: 0.0130 M^2 (Piston area)
Xmax: 3.1800 mm (Cone excursion, linear)
Revc: 6.5400 ohms (DC resistance)
Znom: 8.0000 ohms (Nominal impedance)
Pmax: 35.0000 watts maximum rated power

Driver: MW 6517
BrandL Polk Audio
* Size / Type = 6.50" treater paper cone woofer
* SPL = 91 db @ 1w/1m
* Wattage = 125 Watts RMS / 250 Watts Peak
* Treated cone woofer, rubber surround
* Response = 40 Hz. to 10 kHz.
* Weight = Right a 4 pound ea.
* Magnet = UnShielded
* VC = 1" ( 25 mm)
* Ohms = 4 ohms
* f(s) - 55 Hz.
* Q(ms) - 7.261
* V(as) - 14.60 liters ( 0.516 cf. )
* n(0) - 5.02%
* M(ms) - 18.38 grams
* R(e) - 1.86 Ohms
* Q(es) - 0.048
* SPL - 92 dB @ 1W/1m
* C(ms) - 0.44 mm/N
* Z(max) - 281.50 Ohms
* Q(ts) - 0.048
* L(e) - 31.08 mH
1 Driver Type Q BL Compliance DC Resistance Fs

3 MW 6501 1.470 5.96 N 3.250 E - 3N/M 7.750 Ohms 31 Hertz
4 MW 6502 1.970 5.16 N 1.470 E - 3N/M 3.520 Ohms 44 Hertz
5 MW 6503 1.820 5.24 N 3.550 E - 3N/M 6.540 Ohms 29 Hertz
6 MW 6509 2.100 4.57 N 3.540 E - 3N/M 8.970 Ohms 30 Hertz
7 MW 6510 1.390 6.32 N 3.410 E - 3N/M 6.570 Ohms 31 Hertz
8 MW 6511 1.405 4.34 N 3.496 E - 3N/M 3.130 Ohms 29 Hertz
9 MW 6512 1.905 4.99 N 1.588 E - 3N/M 3.466 Ohms 40 Hertz

emaraszek

Update: Bought a pair of 5As this past weekend with the Peerless tweeters and black basket MW6500s. Swapped those parts over to the 7Bs, so they are now fully functional.



Thanks to all who helped out in this thread!

Also, I now have some 5A parts (cabinets, PRs, crossovers), a set of Midwest knock-off Peerless tweeters, and a spare 7514 Peerless tweeter if anyone has a need.

Faustin

Glad that things worked out. I know many here really like the Monitor 5, but I had a pair with the Peerless tweeters, I rebuilt the crossovers and I never thought they sounded very good, especially compared to the 7's. I ended up giving them to a friend. I think you made a good decision to swap parts to get the 7's up and running again.

emaraszek

Thanks, I've gathered from other posts on here that the 7s are definitely the better speaker when compared to the 5s. I had the 5s hooked up for a few minutes to make sure everything was working before I swapped parts and I too preferred the 7s

Davedev07

I just bought some 7b’s. One is much quieter and no base, but since it is a passive radiator….. I’m a little confused. Tweeter and mid seem to be working.. Any thoughts? I have 10bs and some 5’s, and had to experience these, I sure didn’t need them..

pitdogg2

Like it doesn't have a bottom(base) or it has no low end (bass)
😬

Check for frozen midwoofer and air leaks.

BlueFox

Test.