Rings of Power (or, What Evil Weed Have I Been Tolkien)
Schurkey
Posts: 2,101
I've been playing with my 1Bs; the original intent was to swap SDA inductors from the original 9.6mH air-core jobs to 9.6mH iron core, larger-gauge, lower DC-resistance jobs; AND while the speakers were down, to swap the 2-ohm main input resistor for the high-frequency circuit boards to a 1.5-ohm resistor. The resistor swap intended to boost the treble volume a bit in relation to the mid-bass.
As usual, both jobs became far more of a challenge than they had any right to. The two days I budgeted for this disaster is still an on-going effort. I intend to document the inductor change, and perhaps the resistor change separately.
For now, here's my still-incomplete effort to achieve mid-woofer sealing to the cabinet. This became an issue because accessing the interior of the speakers and removing the two small, round crossover circuit boards inside each 1B (or SRS 2 Blade/blade) cabinet was made infinitely more difficult because the LAST time I sealed them up, I used rope caulk (often called "Mortite" (a brand name for rope caulk) on this forum.) This stuff makes driver removal a challenge later on. The rope caulk takes five times (or more) the time and effort to remove than to install. I won't make that mistake again.
Polk used extremely thin, closed-cell-foam gaskets on the back side of each driver and passive radiator (PR). Either those gaskets degrade over time, or they just weren't that wonderful to begin with, or...there's another problem with the driver mounting that permits air leakage and therefore undesirable cabinet venting.
Another member here sells "Rings" with thread inserts; so that the driver and PR mounting does not have to rely on wood screws and the poor thread-holding strength of the manufactured wood-product used to build the cabinets. From the moment I saw those rings, I've believed that a similar product should be used to strengthen and reinforce the actual driver basket mounting. The driver baskets are made from overly-thin metal--stamped and tortured into a 3-D shape to provide some measure of stiffness (but not enough stiffness); four screws on the mid-woofers causes four localized stress areas, and not so much force applied between the screws. I believe that a reinforcement will distribute the fastener stress more evenly around the circumference of the driver basket.
Downside:
I'm not a professional metal-worker. I'm a guy with some tools in the garage. Larry's Rings are beautifully built; I'm more of a blacksmith. MY eight rings show evidence of hand-work versus the laser-cut precision of modern production. Of course, grit blasting and paint will eliminate virtually all the "ugly".
Procedure and methodology:
I tack welded some small nuts onto sheet-metal for use as a locating jig. The magnetic drill was positioned on the sheetmetal with care, and each hole was then drilled into the ring with the best precision an eyeball or two can muster. These holes are the same size as the original screw holes in the driver baskets. Afterwards, each hole is deburred and the ring fitted to my currently-broken (magnet shift) MW6509 to verify hole alignment with the existing mounting holes in the driver. While not "perfect", they are "perfectly adequate" for fastener alignment. The rings will then be hardened and tempered, and given a coating of paint to protect the mild steel from rust. This will also prevent the natural silver color of the rings from being seen through the grille cloth.
Magnetic drill and locating fixture:
Precision drilling with nothing but my nuts to guide me:
Eight (unfinished) Rings of Power, with none to rule them! Still waiting on heat-treat, grit blasting, and paint:
Ring does not interfere with surround roll, but distributes clamping pressure on the rubber that's bonded to the metal of the basket.
Ring thick enough to distribute force, thin enough to not cause diffraction issues. Slightly thinner than formed edge of driver basket.
More to come when I've completed tempering, grit blasting, and paint.
As usual, both jobs became far more of a challenge than they had any right to. The two days I budgeted for this disaster is still an on-going effort. I intend to document the inductor change, and perhaps the resistor change separately.
For now, here's my still-incomplete effort to achieve mid-woofer sealing to the cabinet. This became an issue because accessing the interior of the speakers and removing the two small, round crossover circuit boards inside each 1B (or SRS 2 Blade/blade) cabinet was made infinitely more difficult because the LAST time I sealed them up, I used rope caulk (often called "Mortite" (a brand name for rope caulk) on this forum.) This stuff makes driver removal a challenge later on. The rope caulk takes five times (or more) the time and effort to remove than to install. I won't make that mistake again.
Polk used extremely thin, closed-cell-foam gaskets on the back side of each driver and passive radiator (PR). Either those gaskets degrade over time, or they just weren't that wonderful to begin with, or...there's another problem with the driver mounting that permits air leakage and therefore undesirable cabinet venting.
Another member here sells "Rings" with thread inserts; so that the driver and PR mounting does not have to rely on wood screws and the poor thread-holding strength of the manufactured wood-product used to build the cabinets. From the moment I saw those rings, I've believed that a similar product should be used to strengthen and reinforce the actual driver basket mounting. The driver baskets are made from overly-thin metal--stamped and tortured into a 3-D shape to provide some measure of stiffness (but not enough stiffness); four screws on the mid-woofers causes four localized stress areas, and not so much force applied between the screws. I believe that a reinforcement will distribute the fastener stress more evenly around the circumference of the driver basket.
Downside:
I'm not a professional metal-worker. I'm a guy with some tools in the garage. Larry's Rings are beautifully built; I'm more of a blacksmith. MY eight rings show evidence of hand-work versus the laser-cut precision of modern production. Of course, grit blasting and paint will eliminate virtually all the "ugly".
Procedure and methodology:
I tack welded some small nuts onto sheet-metal for use as a locating jig. The magnetic drill was positioned on the sheetmetal with care, and each hole was then drilled into the ring with the best precision an eyeball or two can muster. These holes are the same size as the original screw holes in the driver baskets. Afterwards, each hole is deburred and the ring fitted to my currently-broken (magnet shift) MW6509 to verify hole alignment with the existing mounting holes in the driver. While not "perfect", they are "perfectly adequate" for fastener alignment. The rings will then be hardened and tempered, and given a coating of paint to protect the mild steel from rust. This will also prevent the natural silver color of the rings from being seen through the grille cloth.
Magnetic drill and locating fixture:
Precision drilling with nothing but my nuts to guide me:
Eight (unfinished) Rings of Power, with none to rule them! Still waiting on heat-treat, grit blasting, and paint:
Ring does not interfere with surround roll, but distributes clamping pressure on the rubber that's bonded to the metal of the basket.
Ring thick enough to distribute force, thin enough to not cause diffraction issues. Slightly thinner than formed edge of driver basket.
More to come when I've completed tempering, grit blasting, and paint.
Post edited by Schurkey on
Comments
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Nice work!
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Very Nice work.. I'm in process of doing something similar to what your doing, the only difference is my rings are made of aluminum and I'm going to install 1/4" standoffs in them. This way the standoff is applying pressure around the hole. I also want to anodize the rings in red the same color as my crossover plates.
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I may not be envisioning this properly, and if so, please forgive me.Very Nice work.. I'm in process of doing something similar to what your doing, the only difference is my rings are made of aluminum and I'm going to install 1/4" standoffs in them. This way the standoff is applying pressure around the hole. I also want to anodize the rings in red the same color as my crossover plates.
Aluminum is far less stiff than steel given similar dimensions. If the standoffs are specifically intended to apply pressure around the screw hole, you are discarding the benefit of applying pressure more evenly around the whole of the driver basket. My intent with the rings I'm building is to "even out" the pressure applied by the four fasteners so that the area between the screws is appropriately forced into the gasket--and therefore into the cabinet recess--while not (overly) stressing the area immediately adjacent to the fastener.
I'd just love to see the actual product you're planning--I may be completely off-base in my mental image and therefore completely wrong in my assessment of how they'll reinforce the driver basket.
Red, huh? I've been wondering about color. Really, I expected to shoot them black and make them disappear behind the grilles. Then I think that if I've gone to all this trouble...maybe matte silver ain't so bad, and if the things show through a little...that's OK too. Or my "Trademark Green"; but that will neither show through nor match anything else on the speaker; in fact it would outright clash with the Wood Grain Vinyl, and is therefore something of an objectionable waste.
One thing I do expect: If you're building them, the workmanship will be perfect. PHOTOS, PLEASE??? -
You guys always amaze me,very nice
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I like this approach. I've drawn up a similar thing in some CNC design software, for the day that I work on another pair of vintage Polk's (like my 5 pairs). The ones I drew up have a double depth, to apply pressure to the basket and the surround, and a small notch for the polk audio logo on the rubber. I planned an eased edge where the aluminum meets the rubber. I am glad to see someone else approaching this.Polk SDA SRS 2
Polk RTA 15tl
Polk Monitor 7C
Polk Lsi9
Infinity RS-II (modded)
Infinity RS-IIIa (modded)
Infinity RS 2.5 x 2
Magnepan 1.6QR (modded)
System: http://forum.audiogon.com/cgi-bin/fr.pl?vevol&1290711373 -
My only concern is the preasure on the rubber surround. I'm not sure about sandwiching the rubber and applying preasure. This is why I decided to do it with the standoffs, also keep in mind these drivers have a flange to stiffen up the driver.
With the driver moving in and out I would hate to find out this shortened the life of the rubber surround and started to split where it was sandwiched.
Just something to think about.. -
With the driver moving in and out I would hate to find out this shortened the life of the rubber surround and started to split where it was sandwiched.
This was my thought too, Larry. That's why I designed a precise double depth, to apply pressure evenly to both the surround and the basket (one gets compressed, the other gets compressed the exact same amount, so no relative compression between the two-besides the obvious fact the fact they are two different materials). I also pulled the metal back away from where the half-roll meets the glued-down area by about 2mm. I agree that if the edge of the metal is right up on the start of the half-roll, and has a hard edge to it, the possibility for fatigue cracking in the rubber over time is something to consider. Schurkey, I think a good eased/slightly radiused edge where the ring meets the rubber next to the start of the half-roll may alleviate some of this concern. Plus having the inside diameter of the ring a couple mm (or so) larger than the outer diameter of the half-roll.Polk SDA SRS 2
Polk RTA 15tl
Polk Monitor 7C
Polk Lsi9
Infinity RS-II (modded)
Infinity RS-IIIa (modded)
Infinity RS 2.5 x 2
Magnepan 1.6QR (modded)
System: http://forum.audiogon.com/cgi-bin/fr.pl?vevol&1290711373 -
The notch around the Polk logo will be a stress riser. Use a generous radius for the notch. "I" wouldn't (and didn't) notch them. The Polk logo is too small to see from the listening position; if you're close enough to see the logo, you are too close to listen to the speaker.I've drawn up a similar thing in some CNC design software, for the day that I work on another pair of vintage Polk's (like my 5 pairs). The ones I drew up have a double depth, to apply pressure to the basket and the surround, and a small notch for the polk audio logo on the rubber. I planned an eased edge where the aluminum meets the rubber. I am glad to see someone else approaching this.
The drivers have a raised lip at the OD; and this does stiffen the driver basket. To my way of thinking this lip is not enough. If the basket were made from thicker metal, if there was a larger lip, or if they had stamped-in concentric ridges to further stiffen the metal...the Rings we're all making wouldn't be needed. Truth is, those speaker baskets are pretty flimsy--and the weakest part of the whole deal is the mounting flange.My only concern is the preasure on the rubber surround. I'm not sure about sandwiching the rubber and applying preasure. This is why I decided to do it with the standoffs, also keep in mind these drivers have a flange to stiffen up the driver.
With the driver moving in and out I would hate to find out this shortened the life of the rubber surround and started to split where it was sandwiched.
Just something to think about..
There's considerable contact area between Ring and rubber; I don't expect problems given the wood-screws or 8-32 machine screws used to attach the driver. There just won't be enough "squeeze" to damage the rubber of the surround. In fact, I'm COUNTING on this; a certain amount of torsional twist in the Ring is part of my theoretical operating principle for spreading the load away from the driver basket at the screw holes, and into the metal between the holes.
It IS worth thinking about; and I'll have a better handle on this in a day or three when I actually install them on my speakers.
I have NOWHERE NEAR the machining capacity to add this to my design, even if I wanted to.This was my thought too, Larry. That's why I designed a precise double depth, to apply pressure evenly to both the surround and the basket (one gets compressed, the other gets compressed the exact same amount, so no relative compression between the two-besides the obvious fact the fact they are two different materials).
HOWEVER, it would be easy to pick up some appropriately-thick solid wire, make a wire circle just slightly smaller than the OD of the ring, and use the wire as the "step" to control the crush of the rubber.
In truth...I don't think that is even remotely needed. I just don't expect a problem with applying not-all-that-much pressure to the relatively-large area. I'll find out soon enough.
Got that handled; perhaps my photo is too dark to see it appropriately. Ring is totally, completely absolutely clearanced from the "half roll" of the surround.I also pulled the metal back away from where the half-roll meets the glued-down area by about 2mm. I agree that if the edge of the metal is right up on the start of the half-roll, and has a hard edge to it, the possibility for fatigue cracking in the rubber over time is something to consider. Schurkey, I think a good eased/slightly radiused edge where the ring meets the rubber next to the start of the half-roll may alleviate some of this concern. Plus having the inside diameter of the ring a couple mm (or so) larger than the outer diameter of the half-roll. -
The notch around the Polk logo will be a stress riser. Use a generous radius for the notch. "I" wouldn't (and didn't) notch them. The Polk logo is too small to see from the listening position; if you're close enough to see the logo, you are too close to listen to the speaker.
I can hear them from 6 inches away just fine! haha ...moment of levity...
Seriously though, you're right, additional stress will concentrate there....a little bit. The rest of it is substantial enough to not bend. I put the notch in there so that the logo didn't get crushed or the ring sit on an uneven elevation for that small part. Agreed about the radius. For the replacement drivers, you'd never have to think about this at all (no logo stamped on them).Truth is, those speaker baskets are pretty flimsy--and the weakest part of the whole deal is the mounting flange.
Yep, do a really quick screw-down after applying Mortite (not as quickly compressible as the foam)....and watch the rim of the basket distort! A trough where the screws are and a peak in between them!There just won't be enough "squeeze" to damage the rubber of the surround.......
Ring is totally, completely absolutely clearanced from the "half roll" of the surround.
I'm guessing that any damage would be mostly from a very hard 90-degree edge on the metal, working with pressure into the rubber over time. But if that corner were softened (with a quick sanding), the concern (combined with the modest contact pressure over a large area like you mention) might be no concern at all.
And kept away from the edge of the half-roll, I think this is a very good idea. I'm glad you're approaching them and I'm anxious to see how they turn out for you.
G~Polk SDA SRS 2
Polk RTA 15tl
Polk Monitor 7C
Polk Lsi9
Infinity RS-II (modded)
Infinity RS-IIIa (modded)
Infinity RS 2.5 x 2
Magnepan 1.6QR (modded)
System: http://forum.audiogon.com/cgi-bin/fr.pl?vevol&1290711373 -
Great idea guys. Looking forward to seeing some finished products. Could it be that this product(s) also contribute to a stronger/more solid coupling of the MW to the front baffle?"Science is suppose to explain observations not dismiss them as impossible" - Norm on AA; 2.3TL's w/sonicaps/mills/jantzen inductors, Gimpod's boards, Lg Solen SDA inductors, RD-0198's, MW's dynamatted, Armaflex speaker gaskets, H-nuts, brass spikes, Cardas CCGR BP's, upgraded IC Cable, Black Hole Damping Sheet strips, interior of cabinets sealed with Loctite Power Grab, AI-1 interface with 1000VA A-L transformer
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I also want to anodize the rings in red.
Still in love with Cerwin Vega's yep I know its hard to get out from under the CV spell.....
just kidding Larry great idea's from all. -
Three things:
1. I am not sure that there is some deficiency in the stiffness in the basket ring.
2. Unless rubber is designed for high pressure applications, applying constant high pressure will cause the stabilizing chemicals and elasticizing oils to leech out over time. This will cause premature cracking and aging of the rubber.
3. There may be some undesirable damping issues if the rubber surround is further constrained by a ring.Proud and loyal citizen of the Digital Domain and Solid State Country! -
I don't know.....seems like a solution looking for a problem.
If you want to lessen the pressure a bit around the holes, add a black oxide stainless steel #8 washer under the cap screw like many of us have done on the PR's. This assumes one has Larry's rings or Hurricane nuts installed and are using the stock gaskets or Armacell, either of which seals the cabinet perfectly. The use of Mortite creates more problems than it solves, IMO. Personally and upon very close inspection of my mid-drivers after I installed the rings, I don't see any concern with the proper seating of the basket flange. It's actually pretty stiff in that area.
I also agree with the others that it would not be a good idea to apply pressure to the rubber.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 -
Glowing hot, nearly ready for a nice, cool oil quench. I burned up a hateful amount of oxy-acetylene (torch flame is white spot on left). Wrong side of the learning curve. They come out with a black oxide coating; and somewhat warped from heat. Tempted to leave the black oxide coating and not bother painting; but resisted the urge. Bead blasting makes a lovely silver matte finish (not pictured) and also shows up cosmetic flaws that then get touched-up with a hand-file.
Hardened, tempered, blasted, painted. Several coats of "Flat Black"; gloss would be more pretty. If there's a second set, I might try gloss. Front and edges are painted, back-side is unpainted so that paint chemicals can't interact with, or stick to the rubber of the surround.
Set in place on my seized MW6509.
For-real installation on the 1B midwoofers eminent--but not today.
My intention is to build similar Rings for the passive radiators; but that won't happen any time soon. Bigger rings...bigger headache. -
Set in place on my seized MW6509.
Is there enough clearance between the ring's inner edge and the rubber surround so that the rubber won't rub against the steel even under a full excursion?Proud and loyal citizen of the Digital Domain and Solid State Country! -
Outstanding work!!
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That's my hope. By spreading the load from four localized spots (screw holes) to the whole circumference--or as close to the whole circumference of the driver as I can practically achieve--the driver is clamped (sandwiched) more securely to the cabinet. Thin, stock gasket or similar substitute becomes more effective at sealing the cabinet.drumminman wrote: »Could it be that this product(s) also contribute to a stronger/more solid coupling of the MW to the front baffle?
I'm sure.DarqueKnight wrote: »Three things:
1. I am not sure that there is some deficiency in the stiffness in the basket ring.
I can't argue based on scientific principles, merely my hunch that there'll be no problem because I don't think four 8-32 machine screws can apply all that much clamping force. I'll find out, and post an update. I suppose I'll have to do mechanical testing by Ringing only a couple of drivers at first, and then checking them in--what do you suggest? A month? Six?DarqueKnight wrote: »2. Unless rubber is designed for high pressure applications, applying constant high pressure will cause the stabilizing chemicals and elasticizing oils to leech out over time. This will cause premature cracking and aging of the rubber.DarqueKnight wrote: »3. There may be some undesirable damping issues if the rubber surround is further constrained by a ring.
The Ring doesn't touch rubber that isn't glued down on the reverse (basket) side. The "roll" will not ever rub on the ID of the ring. I can't get a proper in-focus photo of the clearance...but there is clearance. Thus the benefit of testing on a ruined speaker driver first--I can push the voice coil completely out of place, and there's no interference with the Ring.DarqueKnight wrote: »Is there enough clearance between the ring's inner edge and the rubber surround so that the rubber won't rub against the steel even under a full excursion? -
I suppose I'll have to do mechanical testing by Ringing only a couple of drivers at first, and then checking them in--what do you suggest? A month? Six?
I don't know. It would depend on the chemical and mechanical properties of the butyl rubber surrounds. Whoever is making the current replacement drivers (Madisound?) should be able to provide some insight.Proud and loyal citizen of the Digital Domain and Solid State Country! -
I can't argue based on scientific principles, merely my hunch that there'll be no problem because I don't think four 8-32 machine screws can apply all that much clamping force.
They apply enough clamping force to evenly squish a piece of Mortite down to the same thickness as a used stock gasket. I'd say that's plently. As for the stock gaskets not sealing well, they do a more than adequate job. In fact, I'd say that with Larry's rings installed you could get away with no gasket material.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 -
Schurkey, have you got them installed yet?Polk SDA SRS 2
Polk RTA 15tl
Polk Monitor 7C
Polk Lsi9
Infinity RS-II (modded)
Infinity RS-IIIa (modded)
Infinity RS 2.5 x 2
Magnepan 1.6QR (modded)
System: http://forum.audiogon.com/cgi-bin/fr.pl?vevol&1290711373 -
No, I'm still working on finding some soldering-iron time to change resistors, and finalize the inductor swap.Schurkey, have you got them installed yet?
Still deciding on whether to Hurricane-nut the cabinets, or if the wood screw holes are still in good enough condition.
At any rate, I don't think there's going to be an update here for a month after the Rings go on, so I can verify the condition of the rubber surrounds. -
I hope they go well for you. I like the way they look, cosmetically. Have you thought about doing a backing ring as well (like Larry's) to make a 'sandwich' around the particle board? I think that would be a great approach.Polk SDA SRS 2
Polk RTA 15tl
Polk Monitor 7C
Polk Lsi9
Infinity RS-II (modded)
Infinity RS-IIIa (modded)
Infinity RS 2.5 x 2
Magnepan 1.6QR (modded)
System: http://forum.audiogon.com/cgi-bin/fr.pl?vevol&1290711373 -
Still deciding on whether to Hurricane-nut the cabinets, or if the wood screw holes are still in good enough condition.
Without Hurricane nuts or Larry's rings your efforts are pointless.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 -
It's not about how many mods are made. In this case, it's a simple matter of clamping force.Without Hurricane nuts or Larry's rings your efforts are pointless.
The wood screw threads in my cabinets are in good condition. Thirty-two, 1/4" longer wood screws would do all I really need. This will probably not prevent me from drillin' some holes, and stuffing in Hurricane nuts; as I already own the nuts and the 100-box of machine screws.
And yet, I have some minor reservations about popping enlarged holes in what are currently perfectly-good cabinets.
What I can say right now: I'd much rather listen to these speakers than work on them. Got all the wood-related gumption totally removed from my psyche today. Had to re-set a toilet, but not before replacing the the metal-and-plastic sewage-pipe flange, and the wood of the floor it sits on. Ugly. Icky. F'n DONE, and glad of it. -
It's not about how many mods are made. In this case, it's a simple matter of clamping force.
The wood screw threads in my cabinets are in good condition. Thirty-two, 1/4" longer wood screws would do all I really need. This will probably not prevent me from drillin' some holes, and stuffing in Hurricane nuts; as I already own the nuts and the 100-box of machine screws.
Right, it's about clamping force and you cannot tighten the wood screws anywhere close to what you can with machine cap screws. It's just not possible no matter what condtion your particleboard baffles are in. Side note: The later models have an MDF baffle.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 -
I completely agree with others here it is absolutely about clamping force and wood screws will not clamp tight enough to warrant even the hint of what you are doing with these. The holes will strip out far before that point is reached. remember you are trying to get enough force to evenly clamp the are farthest from the screw holes, not around the screw, the wood screw are fine in that specific area but will never provide the force you are looking for centered between the screws (at least not with their length and the baffle thickness you are working with. I have toyed with this idea in the past and actually worked it on some DCM Time Windows. Unless you get something behind the baffle that will allow you to pull the ring into the baffle it is a waste of time from a functional standpoint. I would use rings behind the baffle to get the same support between the screws you are going for on the front with the speaker frame and ring. I have never measured it but the baffles are routed to accept the speaker frame so it will be flush. lat leaves roughly 1/2 inch of baffle thickness for the speakers to mount to. granted this 1/2 inch is supported around its exterior by the 3/4 thickness. The baffle is not as inflexible as you may imagine especially in that area. I think you have an awesome idea and I believe the steel is better than the aluminum for the same thickness, and they look great, but don't forget whats behind the baffle or your efforts will be in vain. Imagine using the speaker frames and rings etc to get enough clamping force to make the baffle stronger than it was before the driver holes were cut into it. This will not only make the seal better but reduce baffle flex and the associated distortion it generates.If con is the opposite of pro, is Congress the opposite of Progress?!
Monitor 5Jr, Monitor 5, RTA12, RTA 15TL, SDA 2A, 1c, SRS 2, 1.2TL, CRS, Atrium.
