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Just got me a pair of Polk 7B - One of them doesn't sound right

greenflash

greenflash

Active Member
I've just scored a nice couple of Polk 7Bs, they're indeed quite minty on the outside. And one of the speakers does sound perfect but the other has a "muddy" sound (after trying in a couple of amps) so I'm wondering what could be the cause.. And also if there's some cleaning I can do on my own (not a great tech by the way ;) ) before going to an expert. Thanks!
 
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It may be due to the infamous "magnet shift" of the mid-bass driver. Pull the grill of the offending speaker and with the source's power off push gently on the driver. Do you feel any rubbing or scraping?

Dave
 
Hi @relaximus thanks a lot for your answer! :D While I waited I found that the tweeter in the offending speaker is.. not working at all!
With a lot of boldness (!) I opened it up and found this.. Quite a lot of dirt right?

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Polk used to use a dome tweeter they were quite proud of that they called Silver Coil Dome aka Million Dollar Tweeter because that's what it cost to develop. It used a clear dome material that I think they said was polyaminid/polyamide or something. I remember it was supposed to have been based on a material intended for use as synthetic skin grafts. But according to the local sales rep who handled Polk, air would get inside and cause oxidization so Polk stopped using it and went with a black dome instead.

Maybe your speakers contain those tweeters and one has an oxide issue?
 
No idea :( I know there's 7A, 7B, 7C.. And that the 7C is supposed to be not that good as 7A/7B but .. I don't know really. Should I clean this up?
 
greenflash said:
No idea :( I know there's 7A, 7B, 7C.. And that the 7C is supposed to be not that good as 7A/7B but .. I don't know really. Should I clean this up?
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Umm, no. Can we get a pic of the other tweeter to know what we're dealing with? That tweeter, from the pic you posted, is not worth trying to repair.
 
Don't know without seeing the face of the other tweeter.

I went full-out stupid with mine. Recapped the crossovers, damped the driver baskets and stripped off the walnut-look shelf paper and went with real walnut veneer.

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For me, they are worth the effort.

Dave
 
I guess I'll have to take it the Speakers repair shop to see if they can come up with something, else I'll have to look for some tw replacement..
 
relaximus said:
For me, they are worth the effort.
Dave
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Well I can tell you that the full working speaker sounds.. pristine.. Just listened to "We can Work it out" and I loved it. So, totally, I'm quite happy anyway, I'm sure I'll get this fixed and the price was excellent too!
 
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relaximus said:
This is what they looked like when I got them.
relaximus said:
My 7Bs are earlier models with the Polk modified Peerless tweeter. Yours likely have a different tweeter.
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But wait @relaximus how can you tell the difference? Mine look just like yours! :D I only was able to tell from internet pics when the tweeter has that diagonal strip (as yours, which I assumed was the peerless version) or.. an horizontal strip which is the newer tw version..
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Those look to be Peerless tweeters. It *may* be worth you effort to have the bad one repaired. You'll need to weigh that against the cost and availability of a replacement on eBay.
 
relaximus said:
Those look to be Peerless tweeters. It *may* be worth you effort to have the bad one repaired. You'll need to weigh that against the cost and availability of a replacement on eBay.
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Yeah I'll definitely go for it! A friend of mine, very skilled for this stuff will check it, and we'll see about it.
 
And yes, yours look to be in far better cosmetic condition than mine were when I got them. I can tell you that they are worth a bit of effort and $$ to get back into shape.

I also had a pair of Polk SDA-1's when I acquired these. After rebuilding my 7Bs they actually displaced the SDA's. Whether it was due to room interactions, limitations of placement, upstream components (bridged NAD 2400s at the time) or just personal preference, my Monitor 7Bs displaced the SDAs in my listening space (at that time). They have all been replaced by ADS L1230s in that space (for now). I still have my rebuilt 7Bs waiting patiently to be brought back into rotation within one of my systems.
 
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