Monitor 10 Crossover Rebuild Question

juanbanzai

Good morning. First time post for a long time Polk fan. I have a matching set of Monitor 10s that I'm running off a Sansui G-8000 receiver, and one of the 10s developed a problem that I'm struggling to fix.

First off, let me say that the speakers as a whole sound incredible. My wife and I love our music, and often like it loud. While the left speaker is constantly trying to peel the paint off the walls with it's amazing bass, the right speaker sounds very flat - only about half the bass, with no bottom end presence to speak of - but an almost annoying amount of high-mid end.

More importantly, at a good and loud level of volume, the right speaker bangs/distorts. It sounds almost as if the rubber surrounds on the drivers are torn and both cones are rubbing against the baskets of each of the drivers... Or if the cone is mounted off-center of the coil. However, BOTH drivers are new as of last year. I replaced the old drivers when I thought that they were the cause of the no bass/distortion issue.

Based on the sound characteristics I'm experiencing, I'm leaning toward the crossover being the issue. With that said, I have the schematic for the Monitor 10, but I'd like to know about the best components to use. I've read that SoniCaps are a good choice, but I'd like some input on the entire rebuild process before I go forward. Should I rebuild the crossover on the left speaker so that both match?

Finally, I spoke to a tech at Polk when this problem first showed up last year. He asked whether or not the Monitor 10's cabinet was air tight. When I replaced the drivers, I didn't use any gasket material on the baskets before I placed them in the cabinets...but there also didn't appear to be any gaskets on the old drivers when I removed them. How critical is it for the cabinet to be air tight as far as reproducing accurate bass?

Thanks for taking the time to respond.

Aaron

ben62670

Hey Arron there is a lot of info here on the forum about modding the old Polk's. I use Sonicaps on the highs, and Dayton's on the lows for most of my mods. Mills resistors are used to replace the stock ones. You need to pull the XO to find the exact values of the caps, and R's. There are a lot of variations in the vintage Polk's.
Ben

ben62670

I just noticed this thread is in two places.
Lets keep it in one location.
http://www.polkaudio.com/forums/showthread.php?t=77396

Ricardo

Don't jump on the xover until you are absolutely sure they are the problem (unless you just want to upgrade them, which is a good thing, but first solve your problem).

Scratching noise points to a bad driver. I hear you changed them, but it seems you still have a problem there. Air tightness is important for good bass response, and maybe will also get in the way of the following test: gently press on the passive radiator and see if the drivers move; if they don't, they might be stuck or the cabinet is not tight. If they move and make a scratching noise, they are gone. Polk CS can sell you new replacement drivers.

juanbanzai

When I spoke to the tech at Polk today, he encouraged me to post to both the Vintage Speaker and DIY topics because he felt that sometimes different experts visit each one. My apologies for the clutter.

Incidentally, I tested the drivers with a meter earlier when I started having the sound issues. Both tested fine. It's not so much a scratch noise as it is a distortion/clipping/bang noise.

I'm going to pick the thread up on Vintage Speakers if anyone would care to put out more information.

Thanks. I really appreciate the input.

Aaron

ShinAce

Distortion at high volumes can also be the tinsel leads.

The little wires that jumper from the driver's terminal to the inside of the woofer can smack the speaker. Sometimes they need to be bent to the side a bit. Sometimes they end up touching each other(serious distortion/clipping sounds here). Have a good look to be sure.

If that driver was changed and still makes the same noise, I'd be surprised to found out it was the tinsel leads.