Phase Plug design for MW65xx

Gardenstater

^^^ Awesome Jazzhead, the more the merrier! The thing I still marvel at the most is how much better and real the high hat "tsssss" sound is. There is more tonal accuracy and there is discernable texture in the sound that was not there. Less smearing for sure. My advice to anyone on the fence is to take the plunge, carefully

xschop

Jazzhead wrote: »

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.

Nice addition. Did you add thin felts or paint the cone areas?

gp4jesus

My RTi A7 mids @ Xschop for upgrade.

Thanks in advance Rob.

Tony.

Jazzhead

I painted the cone area with gloss black Tulip fabric paint, thinned a bit. One coat.

xschop

Jazzhead wrote: »

I painted the cone area with gloss black Tulip fabric paint, thinned a bit. One coat.

I still cannot tell the difference myself between felt or painted. Glad you are hearing the sonic improvments that I've experienced. I'm still going thru old jazz CDs listening to the new details being brought forth.

Jazzhead

I was cranking the Rudy Van Gelder remaster of Wayne Shorter's "Adams Apple" (1966), and it just sounds fabulous. It's a big enough change that I am having to play with my speaker toe-in again as the soundstage bubble has become larger. Thanks again for pioneering this mod.

xschop

Wayne Shorter is still relevant and one of my favorites.
If you can get ahold of Bob James' One album remaster, it's a whole new experience. Think I'll listen again on the 8TLs this weekend.

xschop

gp4jesus wrote: »

My RTi A7 mids @ Xschop for upgrade.

Thanks in advance Rob.

Tony.

Worked on the RTi-A design today. I'll true the base interfaces up on manual lathe and test fit Monday before painting (I only have semi-gloss black on hand) then gluing/setting...

gp4jesus

Beautiful work so far, Rob. No rush w/the finishing touches 😊.

So many thanks in advance. Tony

xschop

I believe if you can cut the bass frequencies to these drivers, they will perform even better. Their suspensions are just not designed for low extension especially at higher volumes surely.

plastic_avatar

xschop wrote: »

I believe if you can cut the bass frequencies to these drivers, they will perform even better.

There's a question... Even on things like the SDAs and Monitor 12, with their big honking passive radiators, do they do better when you take away some frequencies and shunt them to a sub?
Less of that low-end distortion in the cones, meaning better control, meaning the phase plugs work even better?
I imagine having a sub that has enough control is a key part, yes?

gp4jesus

xschop wrote: »

I believe if you can cut the bass frequencies to these [mid] drivers, they will perform even better*. Their suspensions are just not designed for low extension especially at higher volumes surely.

*I absolutely, whole heartedly agree! So sorry for the thread derail.

I strongly urge A7 owners who enjoy “spirited listening,” to take steps** to filter** and/or isolate** them from any signals below ~120 hz. Doing so will protect them and improve your mid range SQ.
**1. redirect lower frequencies by XO to a subwoofer.
2. Actively bi-amp the speaker*** For best results, remove the woofer LP filtering.
3. Isolate the mids from the woofers with a divider****
4. All the above!
***tried & succeeded about 6 months after purchase. Stops mid-popping
**** my Tri-amp build thread. Has pics of the same

https://forum.polkaudio.com/discussion/174880/tri-amped-rti-a7/p1

gp4jesus

@plastic_avatar

I don’t see why not.

motorstereo

plastic_avatar wrote: »

xschop wrote: »

I believe if you can cut the bass frequencies to these drivers, they will perform even better.

There's a question... Even on things like the SDAs and Monitor 12, with their big honking passive radiators, do they do better when you take away some frequencies and shunt them to a sub?
Less of that low-end distortion in the cones, meaning better control, meaning the phase plugs work even better?
I imagine having a sub that has enough control is a key part, yes?

FWIW I wasn't pleased with the results when I tried going active with my 1.2tls and cutting them off at 40hz. The bass from the 1.2tls wasn't as deep and when I tried to make up for the shortcoming with my 18'' sub it sounded "unnatural" for lack of a better term. I had to try it though and now I know.

xschop

The 65xx drivers' suspensions ARE designed for low freq reproduction as well as midrange, whereas the RTiA 6.5" mids here rely on "roll-off". What Tony has done is the ideal solution as he described. The plugs will be icing on the mid-cake, especially ridding the heavier dust cap. And they'll look cool too😉

xschop

Test run is a go...

xschop

Cleaned plugs with alcohol and hit with 2 light coats of gloss-black enamel. Close to what trim rings came as. Watching paint dry...





A deeper investigation has that dust cap glue being some kind of very sticky polyurethane perhaps. I was removing any leftover perimeter glue via surgical tweezers and one area of the cap base ring detached easily. So removing it and glue entirely... Extra time well worth the bonus weight reduction an aesthetics....Plus I get to listen to Donald Byrd and Stanley Turrentine on the 5Bs.😁

xschop

I just need to find that elusive black marker for the short VC area that protrudes past the cone.

Tony M

You're amazing!

plastic_avatar

What solution did you use to clean up the last of the glue?

Looks fantastic.

Gardenstater

I found this info. when researching phase plugs before I did mine. It is from SEAS who employs them in their driver designs quite often:

xschop

plastic_avatar wrote: »

What solution did you use to clean up the last of the glue?

Looks fantastic.

70% isopropyl alc.

gp4jesus

Looking b e a utiful. You are the man, Rob!

xschop wrote: »

I believe if you can cut the bass frequencies to these drivers, they will perform even better. Their suspensions are just not designed for low extension especially at higher volumes surely.

In connection w/Rob’s comment to anyone interested in dabbling behind my footsteps, I forgot to mention earlier, start w/a mid HP @ 125hz - that’s Polk’s purported spec. I’ve always had 4th order available so I can’t guarantee lower order @ 125 will work. To protect Rob’s meticulous work, gonna try higher frequencies, not to exceed 300hz.

Rob: PM to you later tonight

xschop

You can play them as low as you want. You won't faze the phase plug.
I found some time to work and plug the other one so I can mail out Monday.
I would suggest butyl matting entire frame as the shield on back of magnet will ring as well, then use thin layer Power-grab and re-do the inner frame foam pieces...

Tony M

I can't tell it wasn't done at the original factory when it was designed when new.

NICE JOB!

gp4jesus

I’m w/ya 100% on the butyl matting.

+1 w/Tony M!

xschop

These were definitely fun. I learned some more Polk manufacturing practices. I think the Lsi-X drivers would be the same process to get them done and would convert a set when the time comes.

Jazzhead

So, I've been reading about phase plugs and they supposedly prevent the cancellation of certain frequencies at the top of a driver's intended range. Seems to be the case. After living with these a while I'm hearing instruments/sounds that I have only heard a "suggestion" of before. Especially involving percussion - like steel drums, cymbals, etc. where there is a tone present where before it was just "one note". But it's present across the entire spectrum as well (vocals) Interestingly, imaging has become ridiculous for these old speakers (and they were good before). The original Polk materials that came with my speakers recommended a full toe-in toward the listener. As these speakers have continued to improve I have reduced that to almost none and I have a huge soundstage and the speakers are now profoundly disembodied. I'm for anything that makes the timbre of any instrument more realistic, and this mod really does that. Good stuff.

xschop

The separation definition of male/female vocals by old school duets really caught me off guard.
Never thought I'd delve into Ashford and Simpson era stuff, but it's also new sonic experience as well.

Minnie Riperton makes Mariah Carey sound haggish.

Gardenstater

How many of these little silver bullet gems are out there in the wild uninstalled? Step right up, everyone's a winner!