Repairing Model 11 speakers

1ShotBill

I'm in the process of improving our Model 11 (AKA: R.T.A. 11 or Monitor 11) Polk loudspeakers.

While poking around inside the cabinets, I noticed dark foam baffling glued to the inner chamber underneath one of the two mid drivers. Both of my speakers, which look like they've never been opened up before, have this below the 'inside' driver. Since these are mirrored pairs with specified left and right speakers according to original stickers on the back, by 'inside' I mean to say the drivers closest to center. The baffling has broken down due to old age and one has fallen down to the bottom of the cabinet where all of the white baffling is located under the passive radiator.

Does anyone have experience replacing these foam pieces? I'm wondering whet function they serve. My guess it that they partially seal off one of the upper chambers, but I'm not certain. How important is it to find the same material as a replacement?

Here's a picture of the foam baffle on its own:

Here's a pic of our Model 11 speakers:

These loudspeakers are rare, and were only made by Polk Audio for about one year in my understanding. They're in large, wide SDA-style cabinets and have Peerless tweeters. Please don't mistake these for the thinner RTA 11t towers, Monitor 10, or SDA series.

Thanks!

mdaudioguy

Here you go:
http://www.polkaudio.com/forums/showthread.php?116325-Heads-up-for-Monitor-11-owners

I've yet to do this, as mine have been in storage for some time now. However, they're due to return to action later this year, so we'll see.... Good luck, and keep us up to date with yours.

Yahzi

Good luck.

halo71

Damn those are some nice looking speakers!

1ShotBill

Thanks a million mdaudioguy!

68triumph

Does anyone have a fix for the low end response on the model 11 monitor speakers. I recently purchased a pair and both have the same issue. They are completely original and aren’t marked left or right. Also the build date inside written on the speakers is 2/18/82. All three speakers work but the cabinet has zero bass. If anyone has any experience with this please contact me. Thanks. 68gt6

audioluvr

Sounds like your cabinets are leaking air.

F1nut

68triumph wrote: »

Does anyone have a fix for the low end response on the model 11 monitor speakers. I recently purchased a pair and both have the same issue. They are completely original and aren’t marked left or right. Also the build date inside written on the speakers is 2/18/82. All three speakers work but the cabinet has zero bass. If anyone has any experience with this please contact me. Thanks. 68gt6

Welcome to Club Polk.

There are only two active drivers, the big one is a passive radiator.

Air leak test, push the PR in and hold it in while watching the two drivers, which should pop out immediately then slowly recede. If they fully recede faster than 3 seconds you have an air leak.

Posting pics is always helpful.

68triumph

Thanks, I will try it out tomorrow and I can also post some photos then. Where do they normally leak, I did notice when I pulled one of the drivers out there wasn’t much sealing material under the outer flange edge. I hope this is the issue and not something in the crossover.

pitdogg2

Gaskets are paper thin.

68triumph

Thanks for the input, I did the test and no noticeable movement on either driver. Same results in the other cabinet. So there must be some bad leaks in both.

boston1450

Did you try snugging up all screws on woofers tweeters passives & binding plate/cup on back ? Try not to over tighten them. Just a thought.... I owned a pair of Monitor 11's years ago & I don't have my notes available to explain the difference between the R&L speaker placement. Mine were tagged & I also marked them (as they were just sticker tags IIRC). I did spike them with outstanding results. I removed the base on bottom. Pictures were posted here somewhere

JayMX

68triumph wrote: »

no noticeable movement on either driver.

If the 6.5” drivers don’t move when you push on the passive radiator, it could be that your magnets have shifted, pinching the voicecoils. This can happen if the cabinets get dropped or bounced sharply. Can be fixed with some luck and the right tools.

https://forum.polkaudio.com/discussion/163992/magnet-shift-repair-is-easy/p1

boston1450

He stated all driver were working. No movement when doing PR air test

F1nut

I think it would still be a good idea to check for shifted magnets.

68triumph, with your finger tips spread evenly around the cone gently push in with even pressure. If you hear a scraping sound the magnet has shifted. The key is to apply even pressure.

boston1450

Yeah That is strange to have no movement at all

68triumph

Update, I appreciate all the input, I seam sealed the interior of one cabinet and sealed all of the components including the crossover in the same cabinet, same results. No movement of the drivers, at all. I plan to check the magnet shift next.

Gardenstater

If you've done the gaskets too, I would look really closely at all your drivers and look for cracks in the rubber surrounds.

68triumph

Well both drivers in the first cabinet have magnet shift. I’m working on a fixture to make the repair. I’ve modeled it after a great post about the subject. I can’t find it to thank the author but if someone knows of it please forward Thanks

68triumph

Thanks to all for your input. I did find all of the drivers (4) had magnet shift. I repaired all four with success and they sound great. I know there is a lot of info on this site that addresses the problem so I just want to add a few photos and things that I noticed along the way. I did reseal the inside of the rear board of the cabinets with seam sealer from the automotive world and it was a good fit. Also I modified an already posted pvc fixture setup with eight lower 1/4 fine thread helicoils and used pointed automotive bolts which gave great precision to the alignment of the pole piece/ magnet. The plate closest to the basket seemed ok with four bolts to secure it against the pvc coupler I used. I also used an automotive gasket maker to lightly seal all of the components. Things I noticed were that that it is a strong magnet and hard to pull from the basket, I only pulled by [
















the magnet. It also tries to slam back on when reinstalling. You can pull the-cone back during that process to help from getting damage. I think someone used spacers to help this issue but I missed that thread until I was done. The use of an iPhone to dial in the sound was borrowed from reading another thread I think by The Rev. that was genius and worked great. You can here the voice coil drop into place when you get it right. Another thing is that if you mess up with the glue on the magnet you have time to pull it apart and redo I’m also including a shot of a product for repairing edge nicks in the cabinet that is easy to use and works great, I use a lit match to heat it then apply while wet. The color match is great. I also had to in my case cut the dust caps back enough to view the pole piece to get a starting point to center the magnet. Another thing to check once you have the magnet off is to make sure the pole piece is still attached to the magnet. As a precaution I wicked a small amount of the red locktite around the upper edge prior to starting the repair. If you’ve read this far I’m also willing to ship my fixture out to anyone who may want to try it. I’ll cover the postage if you would be inclined to donate the postage cost to the World Central Kitchen a nonprofit food supplier to places in need such as Ukraine. If there’s a secure way to send your info for shipping please let me know. Thanks

Gardenstater

Nice speakers and nice job! Can't argue with success!

Did you find that the (1/4-28?) threaded holes in the PVC stripped out unless you helicoiled them? Did you have to buy the helicoil kit for that, including special tap?

It looked like, in the picture, you used a combination of the black silicone gasket maker and the Red Threadlocker to glue the magnets?

68triumph

I had trouble with the Phillips construction screws stripping the plastic so I went directly to the helicoils. So I’m not sure that just tapping the plastic would have failed. I purchased an inexpensive kit plus a refill pack for about 20 dollars. As far as the cement I only used the red locktite for the magnet assembly and the gasket maker under the existing factory gasket at the speaker flanges. It’s a bit difficult to remove the gasket maker once dried but I had to do it twice with no issues using a auto door panel removal tool.

Gardenstater

I tend to not use silicone around electronics in general because of acetic acid outgassing but maybe it is less of an issue with the safe for oxygen sensor variety you used. I sure hope you didn't basically glue your speaker baskets into the enclosure and only used it between the foam gasket and the basket and let it cure fully before re-installation of the drivers. In the future I think I'd use something like Ayleen's Tacky Glue or some sort of Rubber based cement.

Let us know what you think of those speakers. They are quite a rare bird.

F1nut

I also used an automotive gasket maker to lightly seal all of the components.

Other than the fact that is a silicone based product, which has no business around electronics, what the heck did you seal with it!?!

68triumph

I thank all of the folks with good intentions on the forum which allowed me to repair a great pair of vintage speakers. I have to say I’m surprised to see my verbiage highlighted and pasted on the president’s post ,this isn’t what I had expected for a collector type of forum. Just a heads up about silicone products that cure, all commercial aircraft use silicone based products including these as pictured, everywhere. Including all cannon plugs (the physical disconnect device that allows instruments and engine components to be quickly replaced ) . After 27 years hands on experience in the airline maintenance industry as a mechanic, I have yet to see corrosion from or have been instructed in avoiding the use of silicone products that cure around electrical components due to corrosion. I’m sure you can come back with something to contradict me but I’ve done the job. Special note to F1 nut , Mr R Dennis is a family friend. I was just trying to add my spin on a repair that others may encounter. I

Thanks again for the valuable information on magnet shift.

Gardenstater

Hmm.....interesting. Turns out there is some that is marketed as "electronics grade" with a "neutral cure formulation" that "will not corrode copper, brass, or silver".

https://www.cslsilicones.com/en/explore-by-sector/electronic-electrical/item/electronics-grade-silicone-sealant-adhesive.html



And there's this stuff here which is "safe for use on or around electronics"

......"the non-corrosive curing system of ASI 388 makes it ideally suited for protecting, sealing and insulating corrosion sensitive electronic and electrical materials such as copper, brass, silver, etc......"

https://www.amazon.com/Clear-Electronic-Grade-Silicone/dp/B0063U2RPW?th=1

PS: I remember a time when I was a young aquarist (aquariumist?) and I decided to take some red shale rocks that I had and adhere them to the inside rear of a 20 gal long aquarium to create an interesting background. I became fully aware of the acetic acid fumes that made my eyes water and my throat scratchy.

F1nut

Do a search for silicone creep.
In addition,

The use of silicones in electronics is not without problems, however. Silicones are relatively expensive and can be attacked by certain solvents. Silicone easily migrates as either a liquid or vapor onto other components. Silicone contamination of electrical switch contacts can lead to failures by causing an increase in contact resistance, often late in the life of the contact, well after any testing is completed.[11][12] Use of silicone-based spray products in electronic devices during maintenance or repairs can cause later failures.