Billet RD-0194/8 tweeter plate design.

xschopxschop Posts: 1,400
edited March 28 in DIY, Mods & Tweaks
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...

6gd8r61ramik.jpg

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

ds6jikxotv3y.jpg

Comments

  • F1nutF1nut Posts: 44,481
    I'm 100% positive the curved face is related to the dispersion characteristics.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."


    President of Club Polk

  • xschopxschop Posts: 1,400
    Design comment noted, thank you.
    Wonder what Stu would say.
  • pitdogg2pitdogg2 Posts: 16,302
    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 GardnerDennis Gardner Posts: 4,866
    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.
    HT Optoma HD25 LV on 80" DIY Screen, Anthem MRX 300 Receiver, Pioneer Elite BDP 51FD Polk CS350LS, Polk SDA1C, Polk FX300, Polk RT55, Dual EBS Adire Shiva 320watt tuned to 17hz, ICs-DIY Twisted Prs, Speaker-Raymond Cable

    2 Channel Thorens TD 318 Grado ZF1, SACD/CD Marantz 8260, Soundstream/Krell DAC1, Audio Mirror PP1, Odyssey Stratos, ADS L-1290, ICs-DIY Twisted , Speaker-Raymond Cable
  • xschopxschop Posts: 1,400
    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.
  • xschopxschop Posts: 1,400
    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....

    ksgbtkcb859q.jpg
  • michaeljhsda2michaeljhsda2 Posts: 1,975
    Looks awesome!
    SDA SRS 1.2TL's
    SDA 1C's w/Clarity Cap ESA; PA, Mills, RD0194-1's
    SDA 2B TL's w/RD0198-1's
    Yaqin MC-30L integrated tube amp
    Yaqin MS-20L integrated tube amp
  • xschopxschop Posts: 1,400
    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...

    dfwdxykrlu1d.jpg
  • GardenstaterGardenstater Posts: 896
    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.
    George / NJ

    Polk 7B main speakers (1979, orig owner)
    Martin Logan Dynamo sub
    Crown D150 amp
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14 gauge, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • xschopxschop Posts: 1,400
    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.

  • GardenstaterGardenstater Posts: 896
    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 :)
    George / NJ

    Polk 7B main speakers (1979, orig owner)
    Martin Logan Dynamo sub
    Crown D150 amp
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14 gauge, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • xschopxschop Posts: 1,400
    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.
  • GardenstaterGardenstater Posts: 896
    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.
    George / NJ

    Polk 7B main speakers (1979, orig owner)
    Martin Logan Dynamo sub
    Crown D150 amp
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14 gauge, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • xschopxschop Posts: 1,400
    Due to the limitation of mold injection, your guess is as good as mine if it translated into the part after cooling.
  • 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.
    The Night is Dark and Full of Terrors
  • xschopxschop Posts: 1,400
    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.

    il4t8wpk5436.jpg
  • RandyCroissantRandyCroissant Posts: 443
    Looking forward to seeing these tweeter bezels, I always thought the original plastic ones were flimsy.
    Yamaha RXA1030, Yamaha CD, Bluesound node 2i, Tidal
    Polk SDA2btl highly modded
    Polk SDA 1C
    Polk CS350 LS x2
    Polk m5jr
    Kimber 8TC
    Sony 55" Bravia
    Wish list SVS sub

  • xschopxschop Posts: 1,400
    I'm half-way thru a batch of the new billet SDA terminal plates and will start the turning jig after that....

    q8ioun04xy8h.jpg


  • la2vegasla2vegas Posts: 4,222
    Looking good.👌
Sign In or Register to comment.

Howdy, Stranger!

It looks like you're new here. If you want to get involved, click one of these buttons!