Help Wanted: Polk Monitor 7B Issues

racingkaherva

Hey Guys-
I'm at a bit of a loss here and would love any kind of feedback you might have.

I bought two pairs of Monitor 7Bs. One pair sounded fine; one sounded a bit thin in the low mids and the upper bass frequencies. I gave the good pair to my friend and kept the other pair thinking a recap would take care of the problem.

The pair I have has very pronounced treble and high-mids. (I should mention both speakers sound identical.) There are really low lows that the passive radiator seems to grab, but there is definitely something missing in the frequency spectrum.

I recapped with Sonicaps and put in Mills resistors and it didn't fix the issue.

The seals seem fine. I hold in the passive radiator and the mid-driver actually doesn't sink at all.

The magnets seem to be fine and I don't see any evidence of driver damage.

The wiring seems to be ok from what I can see. The black/positive wires are hooked up to the the red-dotted terminals. (The MW6500s are marked as being from '82.) Could there be an issue with the inductors? If there was a cold joint anywhere in the circuit, there would be no sound at all, right?

Again, any feedback would be GREATLY appreciated.

Thanks,
Mike

F1nut

I hold in the passive radiator and the mid-driver actually doesn't sink at all.

That's not normal. A small amount of air escapes via the dust cap, so with a properly working driver it will sink back to the resting position.

PolkieMan

If you can find leakage seal the cabinets. Get your friend to swap crossovers for a weekend

TNHNDYMAN

Am I wrong or does the black wire go to ground and the other goes to the red dot? Could be a phase issue.

StantonZ

TNHNDYMAN wrote: »

Am I wrong or does the black wire go to ground and the other goes to the red dot? Could be a phase issue.

No, you were right: (+) goes to black and (-) goes to white. I'm curious to hear the outcome of your investigation.

racingkaherva

Thanks, guys.

I think I'll try checking the polarity of the drivers with a battery to make sure that's all good. Then I will try switching out the crossovers to determine if the issue is in the crossover or drivers/cabinet.

Dumb question: If a frozen driver makes sound, what is the best way to determine if a driver is frozen?

F1nut

A frozen driver will not move. If it's just a shifted voice coil it will make a scratching noise.

Scooterp7

Hopefully this is not posted in the wrong thread.

I am not really savvy about speaker behavior (i.e., wear and tear and degradation).

But, I have a pair of 7B's and am the original owner. I would guess that they have not seen more than 100 hours of use.
Would they require "maintenance" or parts replacement due to just sheer age, or age + limited use?

pitdogg2

Scooterp7 wrote: »

Hopefully this is not posted in the wrong thread.

well if thread jacking is your bag then no you're in the right thread:loneranger:

Scooterp7 wrote: »

But, I have a pair of 7B's and am the original owner. I would guess that they have not seen more than 100 hours of use.
Would they require "maintenance" or parts replacement due to just sheer age, or age + limited use?

Yes you could get better sound with better crossover poly caps instead of the electrolytic's.
Even with no use the 20yo electrolytic's will have dried and shifted some. I believe they were +/- 10% when new.
New poly caps and Mills 12w resistors and you're golden.

racingkaherva

Hi Guys,
Thanks so much for the help so far.

F1nut mentions that the driver should drop due to the air passing through the dustcap; however, my drivers have a glaze or coating over them that seems to make the dustcap quite stiff (and possibly does not allow the air to pass through). It is a bit sticky to the touch. Is this normal?

pitdogg2

racingkaherva wrote: »

Hi Guys,
Thanks so much for the help so far.

F1nut mentions that the driver should drop due to the air passing through the dustcap; however, my drivers have a glaze or coating over them that seems to make the dustcap quite stiff (and possibly does not allow the air to pass through). It is a bit sticky to the touch. Is this normal?

A good picture will helps us help you on this matter.
there should be no glaze on the dustcap. Sticky woofer paper yes dustcap no.

racingkaherva

Ok. I will try to take some pics this weekend of the dustcap. The dustcap is incredibly stiff- as in you can't dent it with a normal amount of pressure.

Another question: I am going to try switching out the crossover with my friend's pair. Do I need to resolder everything for just testing purposes, or can I use electrical tape to hold the connections temporarily? Will there be any sonic difference between soldering the wires to the speaker terminals or just taping them into place?

You guys are great. Thanks again.

pitdogg2

DSkip wrote: »

Might be a better idea just to swap midwoofers between the speakers. You're going to have to remove the drivers to unclip the crossover wires from each driver. This would save you a lot of time and effort.

Sounds like there are soldered to the terminals.
No need for tape you should be able to wrap around terminal if soldered and you unsolder them if that is something you can do.
If you do unsolder put fast-on clips on the wire you can get those at any auto store...size 205 i believe off top of head.

pitdogg2

racingkaherva wrote: »

Ok. I will try to take some pics this weekend of the dustcap. The dustcap is incredibly stiff- as in you can't dent it with a normal amount of pressure.

that is not right.

racingkaherva

Hey Guys,
So I got my friend's 7Bs as well, now. I tried every variable: switching crossovers, drivers, passive radiators, and all I can conclude is the actual cabinets are not resonating quite right. The placement of the foam is pretty much the same, all that stuff.

I have no idea- very strange. One pair sounds lush and warm, the other has a serious emphasis around 3k and is seriously lacking low mids. One has the magic; one doesn't.

StantonZ

That is REALLY weird. I have 2 pairs of 10B's from 2 different years and can hardly tell the difference; I do know the history (owner) of both sets.

satguy08

Do a reseal.

hewlew1

Am I wrong or do the two posts about phasing and the way they should be wired seem to be opposite statements. Posts #4 and #5.

westmassguy

racingkaherva wrote: »

The wiring seems to be ok from what I can see. The black/positive wires are hooked up to the the red-dotted terminals. (The MW6500s are marked as being from '82.) Could there be an issue with the inductors? If there was a cold joint anywhere in the circuit, there would be no sound at all, right?

Going to take a shot in the dark here. What model tweeters do you have, Peerless, SL1000, SL2000?
The MW6500 is an 8 ohm nominal driver. Later model Monitor 5s all used the MW6502s which are 4 ohm nominal drivers.
Describe the crossovers, external fuse or internal polyswitch, capacitor and resistor values?