Phase Plug design for MW65xx

xschop

Mix with water till you get a watery cream consistency then apply a light sheen.

Gardenstater

That's a good thought. What are the Polk cones made of? Anybody know? I'm sure I see a weave pattern.

xschop

They are just cellulose paper and the die they were pressed on had that pattern I believe.

gp4jesus

xschop wrote: »

From your tweeter felt thread pics, those RTi Mids look like 1' VC dust cap sizes.

So in spite of a ~1.5”* dust cap, you believe Polk followed suit w/VC size from their other 6.5” mids? BTW I’m gonna buy the ‘A7 mid - $42 shipped. That allows me to complete the driver mods at my (slow) pace followed by a quick swap. Further, for evaluation** purposes, I want take these mods one step, one driver/channel at a time. I want hear the “inner foam” mod in one channel.
*a quick take w/a tape measurer
**to add to the “inner driver foam” mod’s credibility.

xschop wrote: »

Knowing Polk's Mfg techniques pretty much (1” VC*) is almost a given.

*Yes? Still need some direction to obtain those other 2 driver specs in a previous post. As soon as the driver arrives, I’ll post pics or short video w/ the shield removed. Either that or George can coach me by phone

xschop wrote: »

I'd also be interested in the RTi MW outer ring dimensions. Maybe they could be modded to fit the vintage MW outer edges?

Maybe…
All in good time “Mi tweeker amici!
(Italian for “my tweeker friends”)

Tony

xschop

Besides confirming 1" diameter pole-piece, the length from the top of the pole-piece to the base of cone where it meets spider is needed. This distance determines where the base of the plug needs to begin as I've seen this referenced in some literature about it...

One of Jazz Head's 6500 plugs...

Gardenstater

gp4jesus wrote: »

So in spite of a ~1.5”* dust cap, you believe Polk followed suit w/VC size from their other 6.5” mids?

The dust caps I cut off of my MW6500s all were around 1.5" - 1.6" dia., depending upon how much of the glue you tried to take with it. Dust caps have to be large enough to hide the wires and sometimes they make them large enough to also hide where the wires are soldered to pass through the cone to the tinsel leads.

gp4jesus

Gardenstater wrote: »

@gp4jesus I think you or someone else will have to donate/lend one for dissection to make it happen. I saw some for sale in the flea market I think, for $25.

A7 mid is here ($42 later)!

I think the phase plug mod is off the table for RTi A series mods. Is major disassembly part of the process? The mag shields are glued on!

Side note: 6-7 year old Armacell adhesive sticks to the “peel-off backing too well while separating from the foam too easily! I’ve spent a half hour peeling off just 3” of the same - ARGH!

Gardenstater

gp4jesus wrote: »

Gardenstater wrote: »

@gp4jesus I think you or someone else will have to donate/lend one for dissection to make it happen. I saw some for sale in the flea market I think, for $25.

A7 mid is here ($42 later)!

I think the phase plug mod is off the table for RTi A series mods. Is major disassembly part of the process? The mag shields are glued on!

Side note: 6-7 year old Armacell adhesive sticks to the “peel-off backing too well while separating from the foam too easily! I’ve spent a half hour peeling off just 3” of the same - ARGH!

Hey Tony! You could cut the dust cap off the one you care about least, although it shouldn't get damaged if you are careful and don't get too close to the wires. Then you wouldn't need anything but a small ruler to measure the depth from the surface of the cone to the top of the pole piece.

As far as the inside diameter of the voice coil and outside diameter of the pole piece, well that is a bit more difficult and I'd want to have a caliper and some shims to determine those, at least close enough. Yes those can be done without further disassembly......of magnet etc..

PS: It would also be good to know the depth of the pole piece relative to the high point of the cone/point where the surround begins. Can be measured with the small ruler closely enough.

gp4jesus

@Gardenstater (George)

Thanks for the encouragement to do the Plugs. My current source of pain is the Armacel.

I’ve been pluggin’ away non-stop for over an hour to peel enough to cover just the exterior of…


…this - almost finished. Should I PU fresh Armacel to do the cone side?

Remember: gonna “foam*” only this driver then swap & listen. During the swap, I hafta do a little BP maintenance as one of these…
*cone side too



…has a loose locking nut inside. Very soon gonna go all in on spades for all my LCR drivers @ both ends - 42 if my math is correct.

Side note: in the market for 1” long gold* plated copper BPs - these are plated* brass. Has ~1/3** the conductivity of copper.
**or less.

Thank. Tony

Gardenstater

Yeah if it was me I guess I'd want to use fresh for the inside, but if you feel that the stickiness is still good then no problem. I cleaned the inside with some alcohol on a cotton swab first. You can cut a trial piece leaving the backing on to check the fit until you get it right and then use that one as the template for the other ones. I'd recommend doing the other area between the spokes too provided it is a decent area and won't interfere with anything.

gp4jesus

Gonna go “fresh.” Also while taking this I discovered a portion of magnet/frame area that demands covering to fall in line w/this mod. Not to further damp the shield - I did that sufficiently. But to prevent unwanted reflection. I hate that I have overlooked this until now.

Fortunately, since I hafta pull all the mids ANYWAY for other reasons… Following the foaming of the cone side*, if I have the energy I’ll swap it in tonight as I’m taking my 12 year old to a place (@6p) less than 5 minutes from Lowe’s…

Notice in the above pic the frame spokes look different from the 6500? Would you complete the cone side then finish outside? Less likely to accidentally stick to “foamless” spokes?

Also see how the spider…



…meets the frame? Are the 6500s like that?

Thanks for reading this far. Tony

Gardenstater

gp4jesus wrote: »

Gonna go “fresh.” Also while taking this I discovered a portion of magnet/frame area that demands covering to fall in line w/this mod. Not to further damp the shield - I did that sufficiently. But to prevent unwanted reflection. I hate that I have overlooked this until now.

Fortunately, since I hafta pull all the mids ANYWAY for other reasons… Following the foaming of the cone side*, if I have the energy I’ll swap it in tonight as I’m taking my 12 year old to a place (@6p) less than 5 minutes from Lowe’s…

Notice in the above pic the frame spokes look different from the 6500? Would you complete the cone side then finish outside? Less likely to accidentally stick to “foamless” spokes?

Also see how the spider…



…meets the frame? Are the 6500s like that?

Thanks for reading this far. Tony

Nope. You have much less area there for reflection, and it looks like the outer spider is more active than in the earlier ones. I'd be inclined to let well enough alone and skip that area in your case as it seems like the angle of reflection would be such that it would not be directed back at the cone. I *would* try to run the spoke pieces up to as close to the spider as you feel comfortable though.

Regarding the order, I didn't have any trouble doing the inside after outside but that was with Dynamat for the outside of the spokes.

gp4jesus

Gardenstater wrote: »

Nope. You have much less area there for reflection, and it looks like the outer spider is more active than in the earlier ones. I'd be inclined to let well enough alone and skip that area…

the spider extends to the frame, absolutely no horizontal space to cover. Spokes very nearly “touch” the spider.

Gardenstater wrote: »

I *would* try to run the spoke pieces up to as close to the spider as you feel comfortable though.

I believe the toughest part is above where spokes meet the frame. Then goes vertical (~1:4”)to then meet the cone’s surround.

Gardenstater wrote: »

Regarding the order, I didn't have any trouble doing the inside after outside but that was with Dynamat for the outside of the spokes.

Is Dynamat as shiny in person as it appears on this forum?

Side note: I believe this driver has break-in to go. It’s kinda stiff compared to my installed mids. Perhaps I should swap them now and “foam” a thoroughly broken in driver.

Waiting for Natale to finish.

Many, many thanks. Tony

Gardenstater

This should've been in the foam inside the basket mod thread but why stop now....

Tony, what I was referring to is the area between the first convolute of the spider and the basket edge. Even though it appears to be a part of the spider still, it is more of a glue flange for the spider and could be a slightly reflective surface. If I *was* going to foam it, it would be the area shown by the red lines. I am still thinking you could just leave it be though, although I would extend the foam on the inside of the spokes up almost to that first convolute, even though it goes over the glue flange for the spider.

xschop

Cut the cap off already...

gp4jesus

xschop wrote: »

Cut the cap off already...

😂😂 I appreciate your eagerness to see this go forward. George: talk to this guy. Explain to him the process.

One step at a time, please. I want to hear these w/ cone side foamed. First the one. Then together.

BTW this driver is the “spare*.” I finished foaming the outside. Then I completed the BP maintenance. Necessary because the BP would spin, not allowing removal of the spades. Had to disconnect from the amp side.
As of midnight, the spare in the cabinet.
*the guinea pig for the plug surgery

If the two kids, four dogs, and other unconnected responsibilities* allow, I’ll foam the cone side of the broken-in mid today; swap; and listen😊.
*some light in-the-crawl-space plumbing** to continue on a back deck. Some tile repair in the master bath.
**necessary part of the backyard face lift

George: gonna send you a PM

Thanks for everyone’s patience.
Tony

xschop

Just razzing you.
It would be interesting to calc. the difference between vintage MW and RTi frame surfaces.

gp4jesus

@xchop so sorry for coming across 😢😞 - not my intent.

@Gardenstater et al



The last 1/4” of spider, the flat part just to the left of the spider ripple has frame underneath. Also if you look carefully…




…the DC is about 1 5/8” while under the cone, the VC obviously much smaller ~an inch by my tape measurer

gp4jesus

@Gardenstater



The last 1/4” of spider, the flat part just to the left of the spider ripple has frame underneath.

xschop

You need the foam on the inside of the frame uprights too.

gp4jesus

Yeah, to me that’s the “cone side” of the frame.

About to lay the first piece😊

xschop

gp4jesus

@Jazzhead:

I included 3-layer Sonic Barrier in my PE order - 2 sheets, likely double what I need for both A7s and my A6 center*, but one speaker at a time.
*between 1 1/2 to 1 3/4 the size for its 2 mids.

Where and how much SB to place in the Mid cavity*?
13.5(D) X 7.25(W**) X 12.25(H) = 1198.97” actually smaller than the calculated .69385 as this does not account closure shape, the port, or the driver itself
**widest dimension



@xschop:
Driver detail update Cone diameter - 4 1/2” ; Including surround - 5 11/16”

@Gardenstater the “ foamed” mid is, in the upper registers of its bandpass* - 125hz - 2.25Khz both LR 4th order, a smidge quieter* and hear a noticeable difference in raspiness . I left the BSC filter “on” during all listening.

Thanks again for everyone’s help. Tony

Gardenstater

You might need to rebalance the channels slightly in the meantime. When will you be able to do the other speaker? Baffle Step Compensation? ........schmanzy fancy!

gp4jesus

Gardenstater wrote: »

You might need to rebalance the channels slightly in the meantime.

meh… yeah I cudda & shudda the last time I was in the “Speaker Setup” menu… thanks for helping me to remember I DO have a balance control. OTOH I think my R Ch’s tweeter is on the way out. Fortunately, PE had sent the 1/10 Dayton tweeters I ordered in the shipment. The other 9 await restock @ the end of June😢.

Gardenstater wrote: »

When will you be able to do the other speaker?

When I get 4+ hours. But I think I’m gonna simplify things by trying to break-in the spare in my shop & finish foaming along the way. Then it’s little more than a swap.

Gardenstater wrote: »

Baffle Step Compensation? ........schmanzy fancy!

😂😂 I have the DSP, why not?! A high cut shelving filter, 6dB slope, corner frequency ~575hz* IIRC.
*per a BSC calculator and a lengthy RTA session

Some pics of tools and an application tip that for which George deserves all the credit.

Place the sticky end.





Then w/the hemostats reach behind and peel while pressing & smoothing from the other side



I corrected one other thing that has bothered me for some time…


They came silver as do rings around mids, woofers, ports, & tweeter* bezels*. Always struck me as tacky. I’ll eventually paint* them all.
*as I replace them



Bad lighting and the camera angle makes ‘em look dark gray.

@xschop after I make the next swap, I’ll begin the “exploratory surgery” for the last pieces of info for the plugs.

Thanks everyone. Tony

xschop

I think what's nice about those mids is they wont need any felt or paint like the MW65xx's to remedy the untreated area left exposed under the dust cap. Id say trim as close as yo can get to the lip of the dust cap itself, but not attempt any of the lip that is actually glued to the cone unless you're a vascular surgeon.

gp4jesus

😂Vascular surgeon😂!

I’m sorry y’all are my ears on this stuff. Nobody here cares one way or the other.

Per my style*, I’m gonna take it slow*. In between everything else I’m gonna go to pg 1 of this thread to carefully examine everyone’s foot steps.
Side note: these cones appear to be plastic or similar w/rubber surrounds**. What’s the 65XX material?
*I make a sloth look like the Roadrunner😂! Too many other unrelated time-consuming projects about half are “honey doos to boot
**should last forever. I have a pair of Meridian M2 speakers from 1983(?) w/ the original rubber surrounds

I’ll keep y’all posted WHEN I think I’m ready to begin the surgery. Meanwhile, though I haven’t done it yet, gonna use a NAD 3020 to power the break-in. Also gonna PM Jack* for some history.
*seller

@Jazzhead or anyone else - Sonicbarrier suggestions, warnings etc? Seems “less is more” is the rule. I also have a bunch of mineral wool at my disposal. But all that for another session

Happy Resurrection Sunday everyone!

Jazzhead

@gp4jesus

Sorry for the late reply, been awol... I've never heard your model of speakers. Experiment and trust your ears. Others more knowledgeable than I can chime in but could start with a 4x5 piece behind the midrange driver and see how they sound. Live with them for a while. Listen to well-recorded music that you have known for decades. The basket foam mod may have an effect as well, so it can be good to do each independently and evaluate. You can go bigger or smaller with SB until you optimize.

xschop

Putting a feeler out here. I'll be making another large batch of these soon and also will be making them for the RtiA midwoofers too. PM if interested. I'm considering doing a conversion service for both models if the RTiA's work out.

Jazzhead

Happy Birthday America and a good 4th to all you fine Polkies. I finally got around to installing the @xschop phase plugs. The "surgery" went well and the sonic results make it well worth doing. I've gained across-the-board clarity and improvement in imaging/soundstage. I'm hearing more realistic reproduction, particularly in the range of vocals, strings, cymbals, drums. As @Gardenstater said these plugs introduce more detail and smoothness. Strings and synthesizers have a more realistic buzz, the overhanging tone of a cymbal between times being struck is very real. I'm getting more sound of fingers sliding on strings. I'm hearing nothing negative. My gear sounds very nice - I was playing Mark Knopler's "Dream of the Drowned Submariner" and it brought tears to my wife's eyes (a clear indication of success). I agree with @Gardenstater when he speculated about how many more speakers Polk would have sold had they sounded like this. That said, they would have sold at a much higher price point relative to the input of materials and labor. If you have the old (65XX) drivers I would definitely add these phase plugs and the @Gardenstater inner driver basket foam mod to the "must do" list. With the right mods these old speakers perform.