Original Monitor 10 Crossover Re-building

Sumbrada77

Hey everyone, I am in the middle of redoing my original series Monitor 10s
crossovers. I will be posting pics soon. For all you DIY people this project is not your everyday crossover upgrades. I know as I just did a Monitor 5b and that was relatively easy. This task has been and is a pain.

First, the series I have uses Peerless Tweeters, MW6500 woofers and SW100 subwoofer. The series I have uses the 1 AMP fuse on the back. I love the Peerless tweeters, and the Polk 10s sound. My main music is acoustic and they shine for that. I find them smooth and not bright but they and my mids have degraded in sound over the years. Thus the reason for the upgrade.

Second, the crossover schematics on the forum do not include this series and they are very different then the 10As. The crossovers are screw, spacer, screw to hold the two layers apart and not plastic tabs. There is no copper laydown on the bottom, all wiring is hardwired to each component as IS all of the speakers (no push on terminals). Thus there is allot of soldering just to get the crossover out of the box to work on. The binding posts are cheap
light weight ones but here is the kicker. The wires and inductor wire are directly wrapped around the screw piece of the post and soldered on. Making
taking them out almost impossible (major negative as I bought good 5 way posts to replace them with. All wiring is black (+) and white (-) 18 guage? wire which I am keeping. Maybe a no-no but changing them would be relatively easy later. Any suggestions, opinions??

Third, the replacement parts I choose were so much bigger that I have had to completely disassemble the crossover and do a different layout. I will post the schematic along with the pics.
My parts I am using are: (The Clarity Caps were as big as the Solens Cap)
1. Solens PPE (black) 33uF 630V Cap. (1)
2. Clarity Cap (black) SA 12uF 630V Cap. (1) Only 1 not 2 as was in the 10 a schematic. (No cap in parallel with the first 2.5 ohm resistor, instead only a 2.7 ohm resistor). I bought (4) and only need (2) oh well!
3. Mills 12W Resistor (black) 2.7 ohm (1)
4. Mills 12W Resistor (black) 3.5 ohm (1) Note: the board had a second 2.7 ohm and not a 2.5 ohm as the 10a schematic had. I am trying a little higher as suggested. can't hurt!
5. Dayton Premium Gold 5-way binding posts. (May not end up using them if I can not get the old ones out. (more extra parts)
6. Parts Express Speaker surround foam. (Original stuff is flat and hard)

Now for the nitty gritty, I had to take all of the drivers out and unsolder the wires to take the crossover out. The right woofer had (2) black and whites connected the left woofer one set. There was a board baffle between the 2 woofers (support?, separate for sound?). the whole top half of the cabinet was packed with acoustic polyester. All wires were labeled with masking tape tabs to ID the connections for later.
Once the crossover was out, then came the fun part. First I noticed only (1) 12uF cap not (2) and (2) 2.7 ohm resistors not (1) 2.5 and (1) 2.7 ohm. Needless to say I had ordered only (2) 2.7 and (2) 2.5 ohm resistors (more extra parts). Next no plastic tabs, screws instead and (1) missing and (2) others loose, not good. I am still looking for the missing screw. Next I look under the top plate, no copper layout, all components hardwired. Hmm this is getting interesting!!! None of the components were strapped or glued down. All were free moving!
I labeled all of the top positions with a sharpie, took the screws apart, unsoldered the inductor line and labeled the underside. I took off all of the parts except the small inductor and started trying to outfit the board with the new parts. NO WAY!! Way to big to fit! I finially took off the inductor and am mounting it underneath so I have space for the top parts. I finially have figured out a layout. All components will be strapped down with nylon ties and alas hard soldered with Cardas tri-Eutectic solder.
This is were I am now, many hours later, ready to re-solder the pieces in. Even with the layout I have it still is going to be a challenge to get it back in the bow. I have dry tested it and may still have to go thru the passive radiator hole and rebuild the last parts in place. More to follow as I get finished. Then its side by side testing with the its original brother.
All comments, suggestions welcome! Thanks for the forum help in preparing for the project!

ben62670

Enjoy your project. It is worth the time, and effort to do for sure.

Ben

F1nut

You can mount the larger caps vertically, if that will help with the real estate issue.

mhardy6647

Original Original Polk Model 10's; with uncoated passive radiators?

Hope you take, and post, lots of photos.
http://www.polkaudio.com/forums/attachment.php?attachmentid=4961&d=1090333966
http://www.polkaudio.com/forums/attachment.php?attachmentid=6294&d=1101932399

heiney9

Sumbrada,

Good to hear from you and glad you could make a good home for that single 5b I sent you. Sounds like you have your hands full with that vintage x-over. You will be very happy with the results even though it's become a PITA to do.

Anxious to see the pics.

H9

Sumbrada77

A little update, I guess they are not orignial 10s by the posts above but are
before the 10As as the crossovers are completely different. Mounting the caps vertically would be even more of a pain to strap down and layout the wiring. It's a definite no for putting in the new binding posts as the solder, resin in the threads make getting them out impossible or almost. Plus having the small inductor mounted on the bottom makes it so there is not enough clearance. I will have to insulate the small posts anyway so I get no problems with the inductor close. No biggy! I am wiring it now and should be back together soon. I will have to add some jumpers to get the wiring right but its doable. I am still taking more pics as I go. Would it be a good idea to coat the wiring points to avoid any cross noise? They were not before but they were farther apart and on the bottom and the inductor was on top. Any suggestions? Thanks and away I go!!

Polk65

mhardy6647 posted a link above which has the crossover that I believe you are describing.
Here is a color photo from a Monitor 7. Does your crossover look anything like this?

Sumbrada77

No Polk65 mine is not that rudimentary. Mine uses the same round phenolic plate the newer series uses and look to be better components. That crossover looks as if it would have been mounted on the back wall. Mine is mounted on the back of the binding post cover plate. That looks really old
and more homemade. Thanks for the post. More later!

Sumbrada77

here's a few pics both from the 5b upgrade and the 10a? upgrade. There will be more. As you can see the ClarityCaps are huge! Enjoy!
Pic 1 is original 5b and Pic 6 is upgraded 5b
Pic 2 is Solens vs. ClarityCap 12uF Caps.
Pic 3 is top view of upgraded 10a and Pic 5 is original
Pic 4 is what was originally to go in the 10a from the Specs I found. As
you can see there is (2) 12uF but the crossover only had 1. It actually
was a bessing as getting (3) of the Caps on would have been a real thrill!

jakelm

Great pics and great job my friend. But one question. Why was the .01 cap added with the 12uf cap? I had personally found no sonic difference with a bypass cap. Did you feel it was needed or made a difference in the sound quality?

Jake

Sumbrada77

Thanks Jakelm, do you still have any of the 3.5 ohm Mills resistors since you
used the 4.5 ohm ones? I could use 1 as I used a 3.5 ohm (only ordered 1, dumb) instead of the 2.5 ohm pair I got along with the 2.7 ohm needed.

Update on the crossover upgrade, I finially finished the crossover and with a little modification to the opening it is done and I have been auditioning them today. After all of the time spent and modifying I would have been happy just to have the speaker work as good as be for. To my very pleasant surprise the change was apparent immediately. Without any break in time the sound was improved considerably. The mids were clearer, more well defined, and had more depth (less muddied), the highs were crisp and clear, and detailed but not overpowering (I think the 3.5ohm instead of 2.7 ohm helped this). The soundstage appears to have widened. So I will keep it one done, one not for a few days to test more then do the other. Included are a couple pics of the finished crossover. Note the small inductor mounted the bottom and all parts used were covered in shrink tubing for insulation. The Clarity Caps came that way.

Note: I have extra parts due to the crossovers being different than was here. Polk forum gets first dibs as I can not send them back. I will post the parts after I finish the second crossover. Should be by the end of the week.
I have extra 12uF caps, 2.5 ohm resistors, binding posts.

jakelm

No, Sum. I rebuilt one 10a and 2 7b crossovers, so unfortunatly no extra parts.

jakelm

You know a question just came to mind. What would happen if the resistors were to be removed from these crossovers and the crossover was just made up of caps and coils. The resistors dont do much more than volume control right? From my understanding, a resistor doesnt filter frequencies. So why would the mids AND highs require one?

jakelm

And whats this 34uF cap for? I ask this because in my short studies of crossover design, only a coil was used for lows and caps for highs.

jakelm

I have an extra 10a crossover. I think its time for testing. Adding and removing parts...

jcaut

The 34uF cap is shunted across the terminals of the midwoofers. It provides a return path (path of least resistance) for the higher frequencies that manage to get through the inductor. A first order filter would only use one component, generally a capacitor inline with the tweeter and an inductor inline with the woofer. This is a second order filter and it has two components.

As to your other question: Besides padding or "volume control", resistors have other functions in crossovers, too. They're often used to "adjust" the effect of other components in the crossover to acheive the proper filter "Q" and phase alignment, if that makes sense. For instance, in the tweeter network in your picture, ther is an inductor and a resistor shunted across the tweeter. Here's what happens: The lower frequencies that get through the cap see the inductor-- whose impedance is lower at low frequencies and higher at high frequencies- as a path of lower resistance. They'll pass through the inductor rather than the tweeter. The resistor in series with the inductor insures that the impedance through the shunt circuit will not drop below 2.7 Ohms.

Jason

jakelm

It does make sence Jason, but a cap filters (blocks) lower Fr from passing. Isnt lower Fr suffering from having a cap in line with woofer?

The reason I'm asking is because my center channel I built, using 2 mw6503's and a peerless tweeter, is lacking something. I dont know what, but it seems its lacking range. It seems like there is a gap between the mid woofer and highs (1000khz-3000khz). I have tried different reisistors trying to correct this, rasing and lowering values for the tweeter, trying to get my highs more pronounced (better range). A wondered why a reisistor was put in place to begin with. I didnt want to start changing cap values without knowing what was going on.


Also , you see in my diagram, there is a .4mH coil and another resistor, can you breifly explain what they are for?

If I were to change this crossover design and make it a 1st order design, what do you think it would sound like? Or do you think , with the drivers I am using, it would not be a good idea?

Jockos

Sumbrada, why did you go with the clarity caps and not solens all the way around?

jakelm

Maybe do this.

jcaut

Probably wouldn't hurt anything to try it that way, but I don't think that it will help.

If you're talking about that 34uF capacitor, then no, it's not hurting the lower frequency response of the woofers. What it's doing is making the roll off slope steeper (at the higher end of the woofer's range). One of the things about crossover design is that if you "block" frequencies in one place, they tend to show up as an increase somewhere else. That cap probably brings up the response in one area (below the crossover frequency) and drops the response in another (above the Fc), as compared to the inductor alone. Also, by changing components that affect the FR in the range where the woofer and tweeter response overlaps, you can create a big dip or a peak depending upon whether you put the two drivers more in phase or more out of phase. It's very hard to say in absolute terms, what changing this or that will do, without measuring and modeling it.

jakelm

So the 34uF cap creates a 12bd roll of instead of a 6db roll off. 2nd order.

What does the second resistor and coil do?. Another 2nd order roll off for the tweeter?

What I think is going on in my custom center is, the roll of is too aggressive. I might try the 1st order crossover design, being I'm not using the same enclosure as the monitor 10, with a 10" PR.

Systems

jakelm wrote: »

You know a question just came to mind. What would happen if the resistors were to be removed from these crossovers and the crossover was just made up of caps and coils. The resistors dont do much more than volume control right? From my understanding, a resistor doesnt filter frequencies. So why would the mids AND highs require one?

Resistors are sometimes used in conjunction with caps or coils to do specific things like notch filters ,impedance equilization,contour networks so they can be used for more things than just attenuating a drivers output.

jakelm

On my extra 10a crossover, I did this. Removed both resistors and left the 12uF bypass cap. I dont know if I'm hearing things, but the speaker just opened up. The whole speaker just seems to have more range. I have nothing to test this speaker out with, I'm just going by ear.

I deleted both resistors. Speakers ohms read 7.2ohms.

jakelm

What do you think about having the 2 12uF caps in series like that? Should I have a derect line at the first 12uF cap after the fuse and have the first 12uF cap as a bypass?

Systems

Not recommended because by removing the resistors you will have dramatically changed the crossovers response.The 2.5 ohm resistor attenuates the tweeters as well as when paralleled with the 12uf cap forms a contour network that is modifying the tweeters response(probably boosting the very high end of its range).Connecting the caps in series without the resistor means the combined capacitance is halved or 6 uf so the crossover point will shift from what the designer intended.

jakelm

GV#27 wrote: »

Not recommended because by removing the resistors you will have dramatically changed the crossovers response.The 2.5 ohm resistor parrelled with the 12uf cap is a contour network that is modifying the tweeters response(probably boosting the very high end of its range).Connecting the caps in series without the resistor means the combined capacitance is halved or 6 uf so the crossover point will shift from what the designer intended.

Thats what I was thinking. But what about bridging under the cap, so the cap would become a bypass cap, with no resistor under it just a straight wire? Or does it have to be a resistor there and cant be a bridge wire?

I just found the speaker opened up after this crossover change.

The bridge at the 12uf would look like this..

jakelm

I believe that the drivers I am using are well built enough to use a 1st order crossover system. I am making small changes, getting closser to a 1st order crossover as I can. After reading many threads about crossover design, the 1st order crossover is the optimal design.

Systems

jakelm wrote: »

Thats what I was thinking. But what about bridging under the cap, so the cap would become a bypass cap, with no resistor under it just a straight wire? Or does it have to be a resistor there and cant be a bridge wire?

I just found the speaker opened up after this crossover change.

The bridge at the 12uf would look like this..

The wire would just short the cap so it would be the same result as just removing it altogether.

Systems

jakelm wrote: »

After reading many threads about crossover design, the 1st order crossover is the optimal design.

There are many very talented designers who think that the 1st is not a good choice for many reasons,but then Theil and Vandersteen use 1st order exclusively and they make some great sounding speakers.

jakelm

Well how would I go about amplifying the very highs of the tweeter without atennuating it?

Would any ohm resistor work for not shorting out the cap? Since I dont want to atennuate the tweeter, can I use a 1ohm resistor, just something there to where the cap will be used?

To achieve a 1st order crossover i would have to do this right?

Systems

jakelm wrote: »

Well how would I go about amplifying the very highs of the tweeter without atennuating it?

Would any ohm resistor work for not shorting out the cap? Since I dont want to atennuate the tweeter, can I use a 1ohm resistor, just something there to where the cap will be used?

To achieve a 1st order crossover i would have to do this right?

You could try the 1 ohm resistor but the caps value should also change but to what?maybe try some thing smaller.

Yes that diagram is a first order filter but it is highly unlikely that those component values are anywhere near optimum.Sorry to be such downer.:(