Billet RD-0194/8 tweeter plate design.
xschop
Posts: 2,081
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)....
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)....
Comments
"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
Wonder what Stu would say.
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.
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
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.
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.
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....
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
This should be much stiffer than a plastic bezel. I hope it translates to less resonance. Very cool.
Polk 7B main speakers, most mods comp. (1979, orig owner)
Martin Logan Dynamo sub w/6ft 14awg Power Cord
Crown D150 amp
Logitech Squeezebox Touch Streamer w/EDO applet
iFi nano iDSD DAC
iPurifier3
iDefender w/ iPower PS
Custom Steve Wilson 1m UPOCC Interconnect
iFi Mercury 0.5m OFHC continuous cast copper USB cable
Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
Custom Vibration Isolation Speaker Stands and Sub Platform
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.
Polk 7B main speakers, most mods comp. (1979, orig owner)
Martin Logan Dynamo sub w/6ft 14awg Power Cord
Crown D150 amp
Logitech Squeezebox Touch Streamer w/EDO applet
iFi nano iDSD DAC
iPurifier3
iDefender w/ iPower PS
Custom Steve Wilson 1m UPOCC Interconnect
iFi Mercury 0.5m OFHC continuous cast copper USB cable
Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
Custom Vibration Isolation Speaker Stands and Sub Platform
It is interesting that the 194/198s have an ever so slight s-curve. The SL2000s have a slightly different curve as well.
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.
Polk 7B main speakers, most mods comp. (1979, orig owner)
Martin Logan Dynamo sub w/6ft 14awg Power Cord
Crown D150 amp
Logitech Squeezebox Touch Streamer w/EDO applet
iFi nano iDSD DAC
iPurifier3
iDefender w/ iPower PS
Custom Steve Wilson 1m UPOCC Interconnect
iFi Mercury 0.5m OFHC continuous cast copper USB cable
Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
Custom Vibration Isolation Speaker Stands and Sub Platform
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.
This CNC lathe chuck adapter has been an engineering lesson this past week.
Polk SDA2btl highly modded
Polk SDA 1C
Polk CS350 LS x2
Polk m5jr
Kimber 8TC
Sony 55" Bravia
Wish list SVS sub
Panamax 5400-EX
Sunfire TGP 5
Micro Seiki DD-40 - Lyra-Dorian and Denon DL-160
PS Audio GCPH phono pre
Sunfire CG 200 X 5
Sunfire CG Sig 405 X 5
OPPO BDP-83 SE
SDA SRS 1.2TL Sonicaps and Mills
Ctr CS1000p
Sur - FX1000 x 4
SUB - SVS PB2-Plus
Workkout room:
Sony Bravia XBR- 32-Inch 1080p
Onkyo TX-DS898
GFA 555
Yamaha DVD-S1800BL/SACD
Ft - SDA 1C
Not being used:
RTi 38's -4
RT55i's - 2
RT25i's -2, using other 2 in shop
LSI 15's
CSi40
PSW 404
Polk SDA2btl highly modded
Polk SDA 1C
Polk CS350 LS x2
Polk m5jr
Kimber 8TC
Sony 55" Bravia
Wish list SVS sub
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.
Less waxy I might say...