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Polk Monitor 70 Unbalanced

faber12

faber12

Addicted Member
I have a pair of Polk Monitor 70 I got used recently, and after a few minutes of listening to them I noticed that one speaker was louder than the other.

I of course switched them, l/R, and the issue went with the speaker. That eliminated the receiver/wiring as the source of the issue.

I also checked the jumper and binding post connections, the jumpers are gold plated nickel, so no corrosion issues there. These speakers are from 2011, there should really not be anything wrong with them due to age.

I tried pulling the crossovers and looking for anything obvious, but no luck. The one speaker is simply quieter than the other. The whole speaker is that way, not just the tweeter or midrange. Temporarily I have treated the symptom by adjusting the balance control so it images in the center.

Anyone have an idea what could cause this? Thanks in advance.72895.jpg
 
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Have you tested each driver with a multimeter?
May also want to test the drivers in the "louder" speaker for comparison.
You may also want to compare wiring between speakers, in case someone rewired something incorrectly.

Seems that if all that checks out it would be down to the crossover.
Good luck!
 
Yeah my first thought is it's the drivers. Pull them all and measure their DC resistance and you might find your answer.
 
thatToolguy said:
More than likely its a failing crossover cap. As they fail the ESR creeps up and makes the speaker quieter. I had that happen with a pair of speakers recently. New polypropylene caps fixed it.
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It's possible, but unlikely as the speakers are only 5 years old. I've seen it happen before, though, so if the drivers check out then that would be the next thing to look at.
 
Thanks guys, I got them from the original owner, he did not rewire anything, and I tried replacing the tweeter cap in both speakers, and it had no effect.

This leads me to believe it must be driver related, it was just so odd that the speaker would be quieter overall, not just partly, like the tweeter.

I will update when I get a chance to look at the drivers.
 
faber12 said:
Thanks guys, I got them from the original owner, he did not rewire anything, and I tried replacing the tweeter cap in both speakers, and it had no effect.

This leads me to believe it must be driver related, it was just so odd that the speaker would be quieter overall, not just partly, like the tweeter.

I will update when I get a chance to look at the drivers.
Click to expand...

Don't forget to look for any loose connections inside, including bad solder joints. Anything is possible!
 
I will have to pull them open soon, I thought of something, tired as I am today. I should have thought of it sooner.

I removed the jumpers, and tried just the woofers, and the volume was equal. So I was wrong about it being the whole speaker that was off. I then tried the tweeters only, and one is very definitely much quieter. Sorry for that misinformation, my mistake.

I will pull the tweeters and the crossover asap to test further. Hopefully it is just a loose wire, I know it is not the cap. I will examine the solder joints, and check for bad wires and connections internally.
 
faber12 said:
I will have to pull them open soon, I thought of something, tired as I am today. I should have thought of it sooner.

I removed the jumpers, and tried just the woofers, and the volume was equal. So I was wrong about it being the whole speaker that was off. I then tried the tweeters only, and one is very definitely much quieter. Sorry for that misinformation, my mistake.

I will pull the tweeters and the crossover asap to test further. Hopefully it is just a loose wire, I know it is not the cap. I will examine the solder joints, and check for bad wires and connections internally.
Click to expand...

That's good progress. Sometimes we forget about the really simple solutions, looking for much more difficult to find ones. I know I do! I should make a flowchart for speaker repair one of these days, haha.
 
Well, the tweeters read 3.3 ohm on the meter, I will have to check the other drivers as well. I still need to pull the crossover again to look for bad solder joints and such.

The tweeters were somewhat disappointing. I will have to take a picture to explain why...

Maybe they are neodymium motors, but i expected more somehow.
 
I finally got smart, and got time, and swapped the tweeters. One is louder than the other. Darn. Mystery solved though! :) The issue followed the tweeter. I still don't know which tweeter is right unfortunately.
 
Sounds
faber12 said:
I finally got smart, and got time, and swapped the tweeters. One is louder than the other. Darn. Mystery solved though! :) The issue followed the tweeter. I still don't know which tweeter is right unfortunately.
Click to expand...
Sounds like you may want to contact Polk for replacements. It seems the tweeters in the Monitor 70s are a bit fragile, especially when driven by a amp that is at the point of clipping. Maybe the previous owner went a little wild with the volume on occasion. Good luck and sorry to hear that it wasn't a simple fix.
 
I emailed them, probably will hear back tomorrow. The previous owner does like to listen loud, but he also had a Krell KSA-150 that started sending DC to the speakers, especially on one channel. That could have been part of it.

He upgraded to a pair of 901 series VI, and has a good size Yamaha amp he is using now. Those 901s can take some power and then some. :)

He has high frequency hearing loss in one ear, and low frequency loss in the other. These could have been like this from new, and I am not sure he would be able to tell.

Makes me wonder, since the tweeters are measuring exactly the same on the meter, if they were like that all along.

It is actually a simple fix, just need a new driver, thank you all for your assistance on this. If I have issues in the future, I guess I know better how to diagnose and fix.

I do have another question, there appears to be an inductor that shorts out the tweeter leads, it measures like a short on the meter, and connects the trace from the negative tweeter input to the post crossover tweeter positive trace. It is shown as the 0.2 mH coil on the schematic in the op. What purpose does that serve?
 
Thank you Oozure, that explains it perfectly.

I have checked the crossovers against each other, and they seem to be fine, or at least they measure the same.

I got a reply from Polk, here is what they said:

Good morning, this is Ken from Polk Audio. I do have the tweeters. They are 60.00 a piece and the part number is RD0093-1. To order you can call us at 1-800-377-7655 option 2.


$60 is a little more than I had hoped, but probably doable. What I need to do is sell some of my gear, instead of continuing to accumulate it. :)
 
faber12 said:
Thank you Oozure, that explains it perfectly.

I have checked the crossovers against each other, and they seem to be fine, or at least they measure the same.

I got a reply from Polk, here is what they said:

Good morning, this is Ken from Polk Audio. I do have the tweeters. They are 60.00 a piece and the part number is RD0093-1. To order you can call us at 1-800-377-7655 option 2.


$60 is a little more than I had hoped, but probably doable. What I need to do is sell some of my gear, instead of continuing to accumulate it. :)
Click to expand...
Not sure if you are aware or are already a member of the Polk forums. Being a member of the Polk Audio forums may get you a discount. It definitely would get you free shipping. You may be required to make several (1 or 2) posts, I can't recall. Just mention that you are a member of the Polk forums when you call to place your order.
 
Oozure said:
Not sure if you are aware or are already a member of the Polk forums. Being a member of the Polk Audio forums may get you a discount. It definitely would get you free shipping. You may be required to make several (1 or 2) posts, I can't recall. Just mention that you are a member of the Polk forums when you call to place your order.
Click to expand...

I did see something about that, thank you. :)
 
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