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

michaeljhsda2

"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?"

Leaks will result in diminshed bass.

jon s

Push in the passive radiator (the big driver) and see if the the mid-woofers extends out. Hold the passive radiator in position and see if the the other drivers move back to its resting position. If it does, then there defintely is a serious air leak.

If you are going to upgrade the speaker, change the caps to sonicaps and the resistors to Mills. To complete the upgrade, you should also replace the HF drivers with new RDO-194 tweeters. The original plastic domed drivers gets brittle with age and tends to sound harsh plus they also have an annoying 5dB peak at about 12kHz...

juanbanzai

Thanks for the reply, folks. I did indeed do the test where you push the passive radiator in. Both drivers move out, but then slowly make their way back to their "home" position. The tech at Polk told me that this is an expected outcome to this test...but then if the cabinet was air tight, then this movement wouldn't happen. So now I'm confused. Logically, I'm looking for an air leak around the driver and radiator baskets themselves, but I'm wondering if I should seal around the interior seams of the cabinet itself, not to mention where the XO and terminal box attaches to the back. What are the thoughts on this?

Oh...today, the tech I spoke to recommended that I swap the drivers out of the "bad" speaker and insert them into the "good" speaker just to eliminate any possibility that the new drivers are bad. I'm thinking that's a little extreme especially if I go and disturb what seem to already be an air-tight seal on the "good" speaker. Am I on the right track with this?

Thanks again,

Aaron

ben62670

The voice coils are vented to help cool them. This is where the air leaks from. Your description of slowly is a good sign. Pull the driver in question and test with a multi meter if you have one. It should read roughly 6 ohms.
Ben

juanbanzai

Hi Ben. I just wanted to post some more findings with my one Monitor 10 that's giving me problems. Rather than work on the speaker in my semi-dark living room, I put the speaker on my work bench and looked every inch of it over using a flashlight to help look around. I was really, REALLY shocked to see that one of the brand new drivers had a slight tear in the rubber surround! I found it by gently pushing on the radiator and heard a wheezing sound. After looking over every inch of the drivers and radiator, I found the tear. I'll call Polk tomorrow and see if I can get it replaced.

But after finding that disaster, I decided to put one of the old drivers back in. Before mounting everything, I got some of that rubber weather strip material and put it around the cut-outs. I mounted all three and did the "push" test again. Oddly, the old driver pops out a ton more than the newer one does. Not sure why that happens or even if that's a problem. Regardless, there's no more air leaks that I can find. The inside of the cabinet is glued up pretty well.

One question I did have is about the polarity of the wires from the XO. I'm assuming that the white wire is the "+", and the black is "-". The old driver clearly has one of the terminal marked with a red blotch...while the newer driver has what appears to be a "-" scored into the bracket that holds the terminals in place. If you can clear that up for me, I'd really appreciate it.

The bad news is after putting everything back together and running some sound through the speaker, it's still banging/distorting on loud drum or bass hits. I also noticed that it has WAY more high-end than the other speaker. I run an EQ with my system occasionally and I have to turn the high end down to almost nothing in order to not have the noise coming out of the tweeter be painful.

So based on this...am I still looking at rebuilding the XO? I'm trying not to get discouraged, but outside of rebuilding the XO, I'm running out of options.

Thanks very much for taking the time to respond. I appreciate the help.

Aaron

F1nut

One question I did have is about the polarity of the wires from the XO. I'm assuming that the white wire is the "+", and the black is "-". The old driver clearly has one of the terminal marked with a red blotch...while the newer driver has what appears to be a "-" scored into the bracket that holds the terminals in place. If you can clear that up for me, I'd really appreciate it.

I knew that was your problem before I read the above. You have at least one, if not both of your drivers wired out of phase. On your speakers, black or blue is positive, green or white is negative.

In addition, the driver with the torn surround was most likely caused by you wiring the drivers out of phase causing the drivers to pop or bottom out, which will damage a surround very quickly.

ben62670

Yes the black wire is the "hot(+)", and the white is the "neutral(-)" . Speaker use alternating current to drive them. I assume this is why Polk chose the color coding they did. If you plan on keeping the speakers long term I would definitely do the XO upgrade, and new tweeters. There is plenty of help here to guide you through it if you are comfortable with a soldering iron.
Enjoy.
Ben

juanbanzai

Thanks again guys for responding. Luckily, that's exactly how I had them wired. The white wire was going to the "-" terminal and the black was going to the "+". I just wanted to be sure based on conventional wisdom and the markings I was seeing on the drivers.

I'm pretty comfortable rebuilding the XO since I restore antique jukeboxes as a hobby and I'm constantly working on old amps and power supplies. What's bothering me is that the cost of rebuilding the XO the way I want is going to be an issue if, after the rebuild is done, the distortion problem is still there.

Unlike a jukebox from 1939 - where a little bit of hum coming from a tube amp is acceptable....in a high end stereo system, everything has to be perfect. There's very little margin for error and that has me nervous because it's uncharted territory for me

Aaron

Systems

juanbanzai wrote: »

Both drivers move out, but then slowly make their way back to their "home" position. The tech at Polk told me that this is an expected outcome to this test...but then if the cabinet was air tight, then this movement wouldn't happen. So now I'm confused.

It happens because the cabinet is air tight.The air you are displacing by pushing in the PR has to go somewhere so the pressure forces the other drivers outward.

juanbanzai wrote: »

I mounted all three and did the "push" test again. Oddly, the old driver pops out a ton more than the newer one does.

Im guessing it has to do with the compliance of the new drivers suspension.In other words its spider and surround are stiffer(less compliant) than older drivers which have had years of breakin.

ben62670

It's easy if you have the soldering skills. All you need to do is pull the old parts, and put in the new. Do one at a time and you are golden:)
Do the new drivers match the old ones. Are they all MW6500's...

fbm211

Oddly, the old driver pops out a ton more than the newer one does.
Just wanted to chime in and let you know that is normal.The newer mids will take a while to break in.100 hours or so.I would replace all the mids, but thats just me.

juanbanzai

The new drivers that Polk sent me are the 6503s. That's the same model of the drivers I took out.

One last question about this and I'll go and order the parts.

The tech at Polk was 100% sure that the distortion/banging I'm hearing is indeed being caused by the XO because (in layman's terms) he felt that dangerous levels are being sent to the drivers because the proper filtering isn't taking place. Not knowing too much about the XO, I have to agree with him. But is he indeed right?

This is something I wish an expert can hear. It's so hard to convey a "noise" or sound issue through a forum.

Thanks again!

Aaron

F1nut

Hmmm......what are describing still sounds to me like something is wired out of phase.

Systems

juanbanzai wrote: »

The tech at Polk was 100% sure that the distortion/banging I'm hearing is indeed being caused by the XO because (in layman's terms) he felt that dangerous levels are being sent to the drivers because the proper filtering isn't taking place. Not knowing too much about the XO, I have to agree with him. But is he indeed right?

Doesn't make sense,I looked at the schem for the Mon10 and the woofers cover the whole bass range.There is no part in the xover that could fail thus causing the woofers to recieve more signal thus causing overexcursion issues.They are already getting maximum low frequency signal as the designer intended.

If your box had a serious air leak that could cause the woofers to overexcursion because they no longer have the restoring force of the air spring to control there motion.

juanbanzai

I got the approval to send the damaged driver back to Polk for replacement. In the meantime, I'm going to go ahead and rebuild/upgrade the XO. I have a question about cap values. I found Solens caps on Parts Express in the 12uf value. However, I didn't find anything in 34uf - which is what the Monitor 10 schematic calls for. When I rebuild a jukebox amp, it's a common practice to try to get caps in a value that's pretty darn close to original - especially if the original cap is 60 years old. For example, if the schematic calls for a 50uf, we put in a 45 because that's "close enough." However, a 50 year old tube amp driving a single speaker is not exactly delivering pristine high-end sound quality.

I'm concerned about trying the same thing in the XO. Parts-Express has a 30uf Solens. Close enough, or should I combine caps to get the actual value needed as stated in the 10's schematic? Also found a 30uf Sonicap. WOW! Are they expensive!

Aaron

ben62670

Use these for the 34uf
http://www.parts-express.com/pe/pshowdetl.cfm?PartNumber=027-944&DID=7
These work well for the highs
http://www.parts-express.com/pe/pshowdetl.cfm?PartNumber=027-430
If your budget allow you may want to get Sonicaps for the highs. They are 20.45 each from soniccraft.com
here is a link to the Mills resistors.
http://www.parts-express.com/mills-crossover-resistors.cfm
Let us know what value resistors you have in your XO's. There were a few XO's that varied from the diagrams.
Ben

Edit: I would not use Solens on the highs. The cheaper Daytons sound much better.

juanbanzai

I will, Ben. In fact...I want to post some pictures of the terminals/wires on the drivers just to be 100% certain that the speakers are not wired out of phase. I'll try and take care of this tonight so that I can order the parts tomorrow when I get a free minute. Thanks so much for all your help.
Aaron

ben62670

No problem. I love this stuff. I love to hear the comments after an upgrade. Reminds me of when I did my first upgrade:)
Take care.
Enjoy.
Ben

juanbanzai

Ben,
I opened up the Monitor 10 and took some pictures of the driver's terminals as well as the XO itself. The pictures show the following:

1) The first one is in response to a question on whether or not the wires from the terminals to the speaker were touching the cone and possibly causing the noise/distortion. The photo shows the position of the wires. It's pretty much the same on both drivers. They aren't touching.

2) This is the terminals on the NEW driver. My eyesight isn't the greatest so I couldn't see the "+" sign on the right terminal until I snapped a picture. The black wire is on this terminal.

3) This is the terminals on the OLD driver. The red blotch indicates the "+" side of the speaker, I assume. This is where the black wire is.

4) Just curious about this....the picture shows the baffling material inside the cabinet. I thought there would be more inside the cabinet behind the drivers and the radiator. The area behind the tweeter is packed solid. Not sure if this is a problem.

5) This is a top view of the XO. The caps are as follows: the two blue electrolytics are 34 uf/50 and 12 uf/50 respectfully. The large yellow cap is a 12uf/100. What I didn't see in the schematic is the small yellow ceramic cap - if that's what it is. It's labeled "-090 852H". The two power resistors are 2ohm 5W and 2.7 ohm 5w respectfully. I almost blew it because the Monitor 10 schematic I downloaded from the Club Polk site shows the 2.7 as 27... but that could be my eyes letting me down.

6) The last picture is a side view of the XO. What's the large coil of wire wrapped around the base of the XO used for?

According to a sticker on the large yellow cap, the date of manufacture is 10/3/89. I hope this information helps. And thanks again!!

Aaron

ben62670

The 50v rating is just the voltage. Any cap you get is going to be 250 or more. No problem. The mustard colored thing is a poly switch. Most people that don't crank their speakers to the point of distortion bypass them. Because of the use of a passive radiator the poly is usually just on the walls with some behind the mids and the tweeter.
The black wire does go to the red, or positive.
Ben

Systems

juanbanzai wrote: »

6) The last picture is a side view of the XO. What's the large coil of wire wrapped around the base of the XO used for?

Its the 1.55mh inductor for the low pass filter on the woofers.

wald0

GV#27 wrote: »

Doesn't make sense,I looked at the schem for the Mon10 and the woofers cover the whole bass range.There is no part in the xover that could fail thus causing the woofers to recieve more signal thus causing overexcursion issues.They are already getting maximum low frequency signal as the designer intended.

First off, sorry to re-direct the flow of the thread...
I believe you what you are saying is correct, based on how mine operate, but why would the designer choose to do this? When I am playing bassy music, such as dance music or dubstep, the 10 will be getting barely any excursion while the mids are bouncing like crazy, straining to pump out the bass. I have to watch where I put the volume so not to damage them. Now certain people who don't share my tastes in music might say that it is speaker abuse, but in my opinion, each driver should be set up to play within its capabilites in proportion to the other drivers. Shouldn't the low pass filter have been moved up a tad? I feel like the 10 needs to get out there and dance! Not complaining since the Monitors sound so darn good for any other genre of music, and they sound so warm and delightful for the music I usually put through them. I actually found this thread when I was searching to see if modding the XO's on the 10's was common because I was wondering myself. I'm thinking of throwing a JL Audio 13w7 into the mix (sorry Polk!) and see what happens there. Maybe I shouldn't expect speakers from 1982 to be designed to play music that is popular in 2009?

Good thread

Mike

EDIT: Ha! There is no flow. The thread is old. But I still am curious about this.

F1nut

Waldo, what are you driving the speakers with? If you have any tone controls, are they flat? Using a clock dial, at what postion is the volume knob when you listen to your dance music or dubstep?

BTW, WTF is dubstep?

wald0

F1nut wrote: »

Waldo, what are you driving the speakers with? If you have any tone controls, are they flat? Using a clock dial, at what postion is the volume knob when you listen to your dance music or dubstep?

BTW, WTF is dubstep?

I'm using an Onkyo TX-8555 which is 100wpc. I know this isn't the best choice, but it's what I have at the moment. I'm looking into getting an Adcom GFA-545 or a Parasond. I have my music playing from my computer with all eq presets off and set to flat. I have the ONK on PureAudio, which disables the video out and display to route power to audio, and makes everything flat except for balance. As far as volume it never exceeds 60/80. It is probably bass distortion causing it I guess. Can anybody tell me what kind of ratio bass takes to amplify compared to mids? Now that I think about it, this dubstep probably should have about 200 clean wpc rather than the probably ~75 they are getting.

Example of dubstep.
https://www.beatport.com/en-US/html/content/release/detail/148778/Hostilis

Just streaming previews.

So yeah I should probably get some 15's or get the Adcoms? LOL

Thx for the help guys.

Systems

wald0 wrote: »

but why would the designer choose to do this? When I am playing bassy music, such as dance music or dubstep, the 10 will be getting barely any excursion while the mids are bouncing like crazy, straining to pump out the bass.

Hi Mike,the 10" is a passive radiator so it has no voice coil thus has no electrical connecton to a crossover or amplifier etc.Its purpose is to augment the low bass of the 2 midbass drivers. The smallish 6.5" midbass's are somewhat limited in regards to deep bass response so they need a bit of help,the addition of the PR will give the system approximately another octave of bass extension.
Like a bass reflex port it is tuned to a specific low frequency and is driven acoustically by the backwave of the 2 midbass drivers not electrically by the amp.For the PR to work properly the low end of 6.5" drivers must not be filtered.

F1nut

Waldo, yep the AVR is the issue. It simply doesn't have what it takes to control the drivers.

wald0

GV#27 wrote: »

Hi Mike,the 10" is a passive radiator so it has no voice coil thus has no electrical connecton to a crossover or amplifier etc.Its purpose is to augment the low bass of the 2 midbass drivers. The smallish 6.5" midbass's are somewhat limited in regards to deep bass response so they need a bit of help,the addition of the PR will give the system approximately another octave of bass extension.
Like a bass reflex port it is tuned to a specific low frequency and is driven acoustically by the backwave of the 2 midbass drivers not electrically by the amp.For the PR to work properly the low end of 6.5" drivers must not be filtered.

Wow thank you for the informative response. I have heard of a PR but I wasn't sure if this an application of one. I'm guessing if they were powered 10's that it would have like 5 times the bass response.

@F1nut. Yeah that's good to hear as well. It means that the Monitors are probably still as good as they are raved, and as I had hoped. Now somebody suggested an Adcom GfA-545, but that is only 100 or 125 wpc if I remember correctly. Solid state, but still, that is only a tad more than what I have.. Shouldn't I go with something more like a solid-state 200wpc to make sure I can properly control the bass? I highly doubt that Polk rated them 20-250wpc if they only wanted 120 good watts running through them. I'm not sure the person who suggested it took into consideration what I was playing through them. My main concern is high quality at good volume levels. Suggestions welcome, and also thanks for taking the time to respond so far.

-Mike

Systems

wald0 wrote: »

When I am playing bassy music, such as dance music or dubstep, the 10 will be getting barely any excursion while the mids are bouncing like crazy, straining to pump out the bass.

Im guessing that this type of music will have a great deal of energy in the mid and upper bass range thus requiring greater excursion demands of the 6.5" drivers.The majority of the signals content may be somewhat outside(above) the operating range of the PR explaining its appearance of less excursion.

F1nut

I'm guessing if they were powered 10's that it would have like 5 times the bass response.

No, not really. PR's are capable of producing clean, deep bass equivalent to a powered woofer many times it's size. As GV pointed out, it's possible that your music has more mid-bass than deep bass, therefore the PR wouldn't see much action. However, I believe with separate amplification you will get better and deeper bass overall. It takes a lot of power to produce bass and it takes an amp capable of high current to control the drivers.