Billet RD-0194/8 tweeter plate design.

xschop

First off, thanks to everyone here that has helped me out with projects in the past. I've learned a lot from you all over the past few years. I've done many mods to these fine classic Polks, some seen and some incognito.
Many posts later, I've gathered enough info that I have decided to make these plates from billet aluminum. Ive made metal plates/bezels before. They sounded great and got rid of the ringing/resonance of the old warped plastic and that's what I plan to do here, as well as upgrade appearance.
Looking back on old posts of the various mods I've done, The RD0194/8 are the ones that deserve the face-lift so to speak.
Thanks to Pittdog for jarring my memory on some aspects to acheive on the upgrade...

The only unknown parameter that I haven't seen anyone discuss, is if the slight 0.090" forward protrusion of bezel curvature is of any significance.
Also there is @ 3 to 5 degrees of the tweeter throat that a straight edge. My friend who is a master machinist familiar with plastic mold injection believes that degree in the throat is only there for the post-injection mold ejection.

Either way, I can add a true radius curvature to the tweeter throat, and I can also accomplish the bezel curvature if deemed necessary via CNC lathe.
Open for all input on this project....

0.160" factory router depth on my 5Bs...



0.090" bezel protrusion (along with warped plastic at the baffle screw mounts)....

F1nut

I'm 100% positive the curved face is related to the dispersion characteristics.

xschop

Design comment noted, thank you.
Wonder what Stu would say.

pitdogg2

Here's my .02

Peerless had an aluminum face plate and most love the tweeter. Peerless made many many different tweeters. My introduction to Peerless was before my time here on Polk. My first "good" speakers I bought with my own money were Cerwin Vega D7's. The horn tweeter I was not in love with. To me it had just one sound. My good friend who actually built sets of speakers for himself and others had used Peerless drivers and Dynaudio drivers. He came to me one day and said we could buy much better tweeters. So he and I plotted some information we had gleened from two sources Cerwin Vega and looking at the XO. We picked a good candidate from the Peerless parts catalog. We needed to disassemble the tweeter to cut the round aluminum faceplate on the tweeter top and botton to be able to fit in between the two mid-range drivers. The fit was almost as perfect as can be with simple dremel tools. The one thing I loved about those Peerless tweeters was that they sounded so much better with the silk dome. So smooth, so articulate. The second thing was the ability to take the faceplate off and replace the "butterfly" as we called them. The silk dome and voice coil could be switched out with a new one. No need to buy a whole new tweeter just the butterfly, 4 screws and back in business. For the life of me I could never understand why Polk never adopted any of these Peerless tweeters that had this ability to just switch the voice coil and dome. It just made so much sense to not have to build the whole driver and the butterfly was only about 6.00 to replace. Peerless made a ton of different tweeters that had that ability to switch the dome and voice coil. The domes to this day are still available for those tweeters that are 30yrs. old. Almost all those face plates were flat aluminum as well. Step ahead 10 years and now there were some Peerless metal faced tweeters that were dome like. My understanding is it brought the dome out away from the speaker face a bit to help negate early reflections from the speaker face that affected the tweeter sound.
There is some science behind it I'm certain of that.

Dennis Gardner

Understanding the response characteristics in tweeters is beyond most of us. Even the angled inner wall of the bezel is a wave guide horn that impacts the response. The sloped outer bezel has been designed to help with diffraction too. You might never be able to hear any differences between a flat or curved bezel, but testing equipment can show them to you in the response graphs.

xschop

F1nut wrote: »

I'm 100% positive the curved face is related to the dispersion characteristics.

I'm 100% positive I can emulate the curve via the CNC. And I'll be doing just that since it seems the consensus here so far. I agree with Pitt that the early peerless are beautiful sounding tweets. I also agree about the rebuildability aspect and I'll be recessing these for the RD0194/8 domes as well as the aftermarket ones we experimented with.
Thanks to D. Gardner for the input too, I'll build them with the factory throat angle just to play it safe. I can always experiment on my own, and curve the throat on a set and sit back with some listening beverages.

xschop

Can anyone confirm 100% if their SL2000 magnet-to-plate holes are different than their 194/198 hole distances?

I gave away my modded set of 2000's and can't find any of my old posts. I thought they were smaller distances by a couple millimeters than their 194/198 counterparts.

xschop

Billet plate showed up finally.

Confirmed that the SL2000 magnet (with the 8 locating dowels/pins) is 41.0mm on square at the tweeter plate mounts taps....

The RD0194/8 magnets (with 4 mounting bosses) are 39.0mm on square....

xschop

michaeljhsda2

Looks awesome!

xschop

Got an adapter plare on the way for the self-centering chuck we'll use. I'll also have to design/machine a lathe holding jig for this project...

Gardenstater

I would've guessed a 4 jaw chuck would've been what you'd use to hold the rectangular blanks. I'll be interested in seeing the holding jig. So I guess you're using 1/4" aluminium stock to accommodate the 0.090" curvature and the 0.160" router depth? What will you do for the waveguide, 0.25" roundover?

This should be much stiffer than a plastic bezel. I hope it translates to less resonance. Very cool.

xschop

The turning jig will be made on a manual lathe 4 jaw, then milled to accept each billet plate after they've been routered for the magnet/dome inset.

The "throat" waveguide can fool you by looking 0.25" deep, however it sets forward at the apex of the curve, while the magnet inset places the dome forward as well.

So F1's point is correct that the dispersion characterists would be skewed if it were a simple flat-plane bezel.

Manufacturers will not go to this extent to make a tweeter bezel at least 10x stronger than the ABS plastic that you normally see.

Gardenstater

Another way to do it (which I'm sure you considered) would be to mill the bezel to it's final curvature with a CNC milling machine and a ball end mill. I'm thinking that way you could get the same shape as the ABS plastic ones, which have multiple curvature radii, other than the spherical surface you'll get with the CNC lathe....unless I'm missing something which is quite possible

xschop

If you're referring to the multiple radii due to all four plastic screws deforming it, then yes it has multiple radii lol.

It is interesting that the 194/198s have an ever so slight s-curve. The SL2000s have a slightly different curve as well.

Gardenstater

That's interesting regarding the s-curve. Maybe the plastic warped in the casting/cooling process?

No I'm thinking that it appears to be the case that the radius of curvature of the bezel in the x-axis direction (horizontal on the speaker) does not appear like it could be the same as in the z-direction (vertical). Either that or they do not have the same centers of curvature, and in either case it doesn't appear (to me) to be possible to duplicate on a CNC lathe.

xschop

Due to the limitation of mold injection, your guess is as good as mine if it translated into the part after cooling.

stainless0steel2

This is just my 2cents. But this weekend I swapped out my stainless bezels and replaced them with the plastic OEM's.
I've been using them since Saturday morning; and honestly I don't hear a difference. If there is a difference if sure it's extremely minute.
But I'm very curious to see how yours turn out, and the results you get. You do some excellent machine work so I'm sure they'll be great.

xschop

I made a set of flat plates to replace the SL2000s in 10Bs. I did not hear a dispersion difference either. I did hear crystal clear, yet smooth response coming from the new silk domes I adapted.

This CNC lathe chuck adapter has been an engineering lesson this past week.

RandyCroissant

Looking forward to seeing these tweeter bezels, I always thought the original plastic ones were flimsy.

xschop

I'm half-way thru a batch of the new billet SDA terminal plates and will start the turning jig after that....

xschop

My attention is back on this project . Did some more research/digging and looks like quite a few Peerless tweets share the RD0 magnet bolt pattern, so they'll bolt up just the same as 194/198's

vmaxer

Looking good

pitdogg2

Sweet

RandyCroissant

Curious how they will sound I am thinking more intricate detail. Anyway looking good.

xschop

RandyCroissant wrote: »

Curious how they will sound I am thinking more intricate detail. Anyway looking good.

Thanks y'all.... Youz guys up north

The only recess is the magnet and coil leads you see there. So the design goal will be weighty and impossible to bend by hand as well as have much better cabinet sealing area around perimeter . All locked down with simple hurricane nuts will also increase baffle stiffness in that area substantially. These will be just as heavy as the thinner flat steel ones I made before, but have the front curvature so F1 can sleep at night hehe.

xschop

Back on this one, again.....1st jig done and tweeter step/lip calculated and radiused.

xschop

xschop

Is this technically audio related? My JBL earphones puked a driver...

pitdogg2

Lol nice

xschop

Found the replacement silicones at the house....
Less waxy I might say...