Monitor 10 rebuild and upgrade

xylocramer

Hi all. I've been polking (haha) around here for a bit and am finally ready to start working on rehabbing my monitor 10's. I currently have 5 that I would like to build to the same spec. I picked them up in a lot of 3 (I will call them triplets), and another set (called the pair). The triplets appear to match and are relatively close in serial number (2 are 5 apart, and the 3rd is 2k away), but are different than the other pair. I've attached pictures of the backs and fronts of each set for reference. The pair have 2 fuses, while the triplets only have 1. One of the triples doesn't have a tweeter or mids at all, and another has bad tweeter.

My goal with these it to more or less make them identical. I want to do the TL mod with the RDO-198's, recap/update everything, possibly dynamat the driver cages, Larry's rings (if I can get some or make some) or hurricane nuts, change out the chassis wires, possibly replace the mids if needed? Either way, I want to make these things the best they can be, but I am very much an electrical noob. While I have been trying to get myself up to speed on working on things like this, I need some help. I can solder and am not afraid to learn. However, it seems there's so much info, some conflicting info out there, as people have the gall to have differing opinions about subjective topics. I have and will continue to use the search function though.

One of my favorite threads so far has been this one from westmassguy: https://forum.polkaudio.com/discussion/149215/monitor-10-rebuild-with-tl-mod/p1

Any and all help would be greatly appreciated, and I'll keep things updated as I go along. I already made some stands for the pair, as they are my main stereo setup right now and sounded much better off the ground. Got the original dimensions off another thread here and made them a little bit taller as I saw Polk had done so in later revisions, but I couldn't find a specific height. Stand can be seen in one of the pictures, has carpet spikes, and neoprene between the stand and speaker.

Tony M

Welcome to the Forum.

I started my Polk audio speaker adventure with the Monitor 10s w/peerless like you have. That was many years ago and I still listen to them often. Yesterday was the latest. Amazing speakers for sure.

I don't have any knowledge of upgrading the cross-overs but that link you provided should be a great guide. A few on here will certainly help you out too.
I also haven't heard the RD-0198 tweeters but know members on this Forum love them as much as those Peerless tweeters.

Your speaker "grill" label is upside down. Spin it around carefully if you can.

NICE stands you built there.

Good luck on your project to make those Monitor 10s the best they can be.

F1nut

Your speakers have the Peerless tweeter, so you're good to go already.

xylocramer

Dynamatted the outside of the basket and foamed the inside of the basket legs of my first PR. Came out OK I think. The ringing when flicked is gone. This one is from the triplet that is missing the MW's and tweeter.




On that note, I do actually have the MW's for this one, but they are both magnet shifted and locked. I've seen there are some people around here that will fix this condition. I'd rather do that than source aftermarket or questionable used ones. Anyone open to doing them for me? I'll of course pay for shipping both ways and services. They are original MW6500's.

A question I have is about the paper/cardboard rings around the surrounds. What, if any, purpose do they serve and should I leave them in place where possible?



Also, does anyone have 2 peerless tweeters for sale, preferably 7514's to match the 3 surviving ones of the 5?

Jazzhead

You might contact @xschop here on the forum for your magnet repair.

Gardenstater

Nice job on the passive dynamat. So you foamed the inside of the passive? What foam and thickness? You beat me to it as even I have not tried a passive yet. I am planning to try some 1/4" thick armacell on my subwoofer just to see what happens.

I never removed the cardboard rings on my original silver basket 6500s. I would theorize they left them on for some anti-diffraction benefit if anything. If you remove them I do not know how aggressive any glue may be and you need to be careful that the surrounds aren't damaged in the process of course. The later black basket 6500s did not have them. I have wool rings on mine currently from VR3's laser cutter.

xylocramer

Thanks jazzhead. I sent him a message.

Gardenstater, I used a 1/4" thick adhesive backed closed cell foam intended for weatherstripping. I know, not ideal, armacell seems to be the foam of choice for this purpose, and I would have preferred to use an open cell foam. I figured something was better than nothing.

For the paper rings, I thought maybe it's supposed to be extra support for the mounting of the surround? In the process of working with the PR, I took off its ring. It was rather difficult and felt sketchy. I'll be leaving all the other rings and might try to attach that one back. Only trouble I see there is at least one of the MW rings is partially blocking one of the mounting screws.

Today I added hurricane nuts on this 5th 10 which I'm using as a testbed/practice for the others. I figure, the inherent 4 are mostly or totally working, if I mess this one up, it's not a huge deal.


Poking around I found some chatter about the internal foam batting (dacon?) on early vs late 10's. These ones all seem to have the full pants batting that is large enough to cover the whole back wall, and a roll up top. From what I read, later ones cut the pants into shorts for better air flow between the MW's and PR. I plan to jorts my batting accordingly.



Recently, I'm feeling emboldened to build my own xovers and attach them to the floor of the speaker, rather than be restricted to rebuilding in the original form factor. I've been checking out VR3 Trey's work and have been inspired. Such amazing work. This will be one of my next challenges.

F1nut

I figured something was better than nothing.

You figured wrong.

Why the hell would you line the PR with foam that's going to suck the life out of the bass!?!

There's no reason to cover every square inch of the PR or driver baskets with Dynamat. A little bit goes a long way.

Leave the cardboard alone.

xylocramer

F1nut, I always seem to find myself wading waist deep in the forums late at night, so my memory is perhaps... fuzzy.

Found the thread again by DarqueKnight with Gardenstater as a key contributor, as well Gardenstater's post with the Vandersteen patents. I also see that you're a skeptic on this one. I can appreciate that. So much of the talk there is miles over my head with all the various measurements etc. Really, I'm just starting my journey here and there's a lot of information to take in.

You really think it'll kill the bass? Should it only be done on driven items? Or perhaps not at all?

xschop

I've personally completed the MW foam-frame mod to 4 sets of vintage Polks now, and it does NOT diminish bass, but only improves the midrange.

F1nut

xylocramer wrote: »

F1nut, I always seem to find myself wading waste deep in the forums late at night, so my memory is perhaps... fuzzy.

Found the thread again by DarqueKnight with Gardenstater as a key contributor, as well Gardenstater's post with the Vandersteen patents. I also see that you're a skeptic on this one. I can appreciate that. So much of the talk there is miles over my head with all the various measurement etc. Really, I'm just starting my journey here and there's a lot of information to take in.

You really think it'll kill the bass? Should it only be done on driven items? Or perhaps not at all?

The foam absorbs sound waves. The PR works off the sound waves from the mid-drivers. Since the foam is absorbing the sound waves directly behind the cone the sound waves reaching the PR are diminished at great deal more than using BH5 on the back wall. So, there is no doubt using foam on the inside of the mid-driver baskets causes the mids to be clearer as the bass is less. It's basic acoustics.

As for foam on the PR basket, why would one want to reduce the bass output, which the foam will definitely do.

BH5 is a well established proven modification that does not affect the bass response.

As for DarqueKnight, the man has 2 PhD's in Electrical engineering and IIRC he removed the foam. 'Nuff said.

xschop

What you should mainly be concerned with is ridding the combing effect of the 10's. Somewhere here are instructions for compartmentalizing one of the MW drivers to each cabinet.

Gardenstater

I never advised doing the inside of the passives with foam, only the actual drivers. Will it do any harm? Doubtful but using 1/4" will be able to absorb more bass than 1/8" for sure. Closed cell doesn't absorb as well as open cell, which is why all acoustical room treatment foam is open cell variety. If you look at NRC charts even for 2" foam you will see that the absorption in the bass regions of the passive (around 60 Hz and lower) are pretty much nill. I can only imagine that it would be nill for the 1/4" closed cell you used. However I think it will have additional vibration dampening affect added on to what you get with the dynamat. There is an old thread where Darqueknight originally did all his basket exteriors in closed cell foam, which he later removed and replaced with dynamat. Doing that on an SRS and a 1.2tl had to be a huge task, perhaps even traumatizing!

Darqueknight did only one basket interior with Armacell foam and he didn't want to proceed on to the audio testing phase unless the stuff was easy to remove, which it was not. Therefore he never proceeded to doing all 16 drivers in his 1.2tl speakers but said he would try his 4 drivers in his CRS+ sometime in the future. He only did Thiele/Small parameters testing which the foam didn't really have any impact upon.

Gardenstater

Also, here is the circa 1983 RTA 11 schematic. Would be interesting to see how a Monitor 10 would sound with this instead of the existing one. It would roll off the MW drivers at different frequencies which should give an improvement on the combing and lobing issues:

Gardenstater

Okay, took me a while to find it. I make so many darn screenshots in my internet....investigations. Anyway, you can see the absorption of even 1" and 2" thick acoustical foam of bass frequencies is pretty much nill. I sure *hope* this puts this to rest now.....

F1nut

Not at rest, not at all.

It's low-frequency sound absorption is ideal for HVAC systems, equipment enclosures, transportation components and acoustical panels

Yet their chart says otherwise, so which is it!?!

Anyway, low frequency sound waves are longer, they need to form. Applying any type of sound absorbing material that close to the cone is going to have a negative affect on those waves forming.

Gardenstater

Unfortunately I cannot find any NRC charts for 1/8" (or even 1/4" foam) probably because the sound absorption in the low frequency areas is literally nearly ZERO, compared to 1" or 2". Absorption is absorption. There is not any effect of preventing the formation of a sound wave without absorption of that energy (as long as air is present). But I will always respect everyone's right to have their own opinions.

Gardenstater

3mm wool felt has an NRC of 0.10 and 5mm acoustic wool felt has an NRC of 0.20 and 8mm is NRC 0.35 but that is the avg. of 250, 500, 1000, and 2000 Hz. Here is a chart for NRC of a 12mm wool felt and you can see that it has an NRC of 0.45 but the NRC at low frequencies is nearly 0. That is about twice the thickness of 1/4" and 4 times the thickness of 1/8".

xschop

Looks like these will be getting phase-plugged. Do the 11's have a peerless tweeter? If so, modding the 10's crossovers would not be too difficult to match the 11's diagram.

Gardenstater

xschop wrote: »

Looks like these will be getting phase-plugged. Do the 11's have a peerless tweeter? If so, modding the 10's crossovers would not be too difficult to match the 11's diagram.

I think it would be super cool because I don't know if anyone has ever done it before. Hopefully the larger 18awg 1.82mH inductor is the same.

The picture in Aug 1982 Audio magazine shows a Peerless:



This is the other pcb layout sketch showing the runs side of the board

https://us.v-cdn.net/5021930/uploads/attachments/4/6/7/2/8/18780.pdf

Jazzhead

@xylocramer , regarding dacron batting, all that material should be positioned up behind the midwoofers, none of it extending into the PR area. Make sure none of it is excessively compressed (air/soundwaves must move through it). You can use a few staples if needed so it doesn't fall down with vibration. You don't want material that can absorb soundwaves in the lower PR area of the cabinet. If no one has mentioned you might look at upgrading binding posts. My original binding posts, of similar vintage, were oxidized and sounded terrible. The comb filtering/lobing business mentioned above is an effect caused by both drivers operating at identical frequencies (Google this). My 12's had the same problem. It manifests itself as poor imaging and soundstaging, a missing "sweet spot" - the ability of your speakers to "disappear". Later Polk versions fixed this problem electronically via the crossover. It can also be mitigated through extreme damping of the outer driver of each speaker (an @westmassguy mod). You then have a mirror-imaged pair. The crossover mod is a more elegant fix (if possible?). I now realize the damping mod worked so well with my 12's because they had an over abundance of midrange output that needed to be hushed in addition to mitigating the comb filtering effect (killed two birds with one stone). Along with other mods my 12's now produce a nicely disembodied soundstage. More info:

https://forum.polkaudio.com/discussion/173834/westmassguys-idea-employing-damping-to-mitigate-comb-filtering-and-lobing/p1

F1nut

From my experience I can say adding just a little too much BH5 to the back wall of a speaker cabinet absolutely kills the bass and that is a good distance from the back of the cone, so it's not hard to reason adding any type of sound absorbing material close to the cone will affect the bass frequencies.

xylocramer

Oh man. So much information, my head was spinning there for a minute. I was up into the wee hours of the morning reading again. Found your thread @jazzhead that you posted. Thank goodness my wife and kids went out of town this weekend, because I have done nothing but read and play with these speakers today haha. I'll definitely be replacing the binding posts on all of them, those flimsy little things need to go.

Some good news. While I was readying some MW's for shipping to Rob for phase plugs and magnet repair, I had a chance to fiddle with the 1 tweeter that wasn't working. Before I realized what I was doing I had desoldered it and forgot to check the polarity of the wires. Found an answer on the forum, black + to red post. Hooked it up in another cabinet to see if maybe something was wrong with the original cabinet's wiring or crossover. Turned it on, boom, making sound. Everything seemed to be ok. Through a process of elimination, my conclusion is this: I think whoever was in this cabinet before me might have reversed the polarity when wiring it up previously. So there's a win. I only need 1 peerless to replace a totally missing one.

At the moment I'm pondering the combing/lobbing issue. My thought is, since I'm currently planning to build a remote crossover attached to the cabinet floor (please tell me if this is a horrible idea) why not play around a little bit and have one of the MW's not kick in until ?~600hz? (or something like that similar to the 11's) rather than go through all the rigmarole of making a box for the outer speakers on 4 different cabinets, (2 sets of mirrored cabinets), and leave a 5th as is. I can 3D print a mounting board and slam 5 of them out like a production line.

Jazzhead

Crossovers, electronics, and the like are out of my league, but others on the forum gravitate to it. My speakers sound decent largely because of the people on this forum (and other forums), and repeated experimentation and evaluation. My greatest asset is that I can recognize what sounds like real instruments and voice as I have been involved with/around it much of my life. Glad you have one less Peerless to replace.

xschop

Gardenstater wrote: »

xschop wrote: »

Looks like these will be getting phase-plugged. Do the 11's have a peerless tweeter? If so, modding the 10's crossovers would not be too difficult to match the 11's diagram.

I think it would be super cool because I don't know if anyone has ever done it before. Hopefully the larger 18awg 1.82mH inductor is the same.

The picture in Aug 1982 Audio magazine shows a Peerless:



This is the other pcb layout sketch showing the runs side of the board

https://us.v-cdn.net/5021930/uploads/attachments/4/6/7/2/8/18780.pdf

Is the 11's Peerless 4 or 8 ohm nom.?

xylocramer

In order to alter the crossover design to effectively make these 10's like 11's where the 2nd MF doesn't activate until a higher frequency, to hopefully eliminate some combing/lobing, here's what I'm thinking.
Working off the original 10 crossover schematics and referencing the 11's posted here, would it be as simple as adding a cap and inductor to the second MF in some combination? If so, would I run them in parallel like the 11's, figure 1. Or run them as a 2nd order crossover and reverse the polarity on the MF connections to counteract the 180 degree phase shift, figure 2. Values yet to be calculated. OR, would I have to have a resistor in here somewhere, or am I otherwise totally off base? Trying to get up to speed on crossover design as fast as I possibly can.




Also, would it be safe to remove the fuse from the circuit?

Gardenstater

That Model 10 crossover schematic is not for the early 10 with the Peerless tweeter. We don't have that schematic so you will have to determine that from what you have in your speaker. But no, what you have there isn't the same as the RTA 11 crossover, which is fairly complicated.

The PCB has 8 traces and then there are 2 more inductors that are not mounted on the board. L2 is actually probably on the binding post cup/spool. Maybe L1 is mounted on the cabinet floor?

xylocramer

Oh, I thought that 10 schematic I altered (found on the vintage speakers pinned schematic congregation post) was for these early 10's. I looked at the crossovers out of my speakers, and everything matches the schematic, with the possible exception of the unlabeled inductors.

No disrespect, just trying to clarify and learn. Perhaps you misunderstood my last post? Those are both what I thought were original 10 schematics that I altered for the 2nd MW, in an attempt to mimic what I saw on the 11 crossover schematic you posted. I could be way out in left field though. Would everything upstream on the MW circuit need to be altered to compensate for the changed values on the 2nd MW?

xylocramer

In other news. The previous owner of the triplets had mounted 2 of them to a wall with lag bolts through the back of the cabinet. One had 2x 1/4" holes and each had a 1/2" hole drilled at various angles. Plugged them with dowel rod and got them all buttoned up and hopefully air tight.

F1nut

L1 is not mounted on the cabinet floor or wall.

Gardenstater

Your speakers have the Peerless tweeter and silver basket MWs? Those would be very early, like circa 1979 or so. You need to check the date on your crossovers. The date on that schematic you got from the archives is 11/26/84. At that time they were probably using the SL1000 tweeter, but maybe the SL2000. I doubt that the Peerless tweeter crossover would have that contour network of the 12uf capacitor in parallel with the 2.5 Ohm resistor, but who knows?

Anyways, just look at the RTA 11 Peerless schematic from 1982. The tweeter only has a capacitor in series with it, not a capacitor in parallel with a resistor followed by another capacitor.

The RTA 11 schematic is very much different in other ways as well. 4 inductors, 4 capacitors, and 2 resistors. It is not an easy task to make the change in my opinion. One would probably want to either get the RTA 11 board from eBay or wire up a crossover on a board of your own making point to point.