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 Post subject: Small tears in RCA 515S2 woofer cone. Best way to repair?
PostPosted: May Sat 04, 2019 5:00 pm 
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Joined: Apr Tue 17, 2012 7:58 pm
Posts: 114
Location: Metamora MI, 48455
Hello,

I'm looking for advice on the best possible method of repairing about a half-dozen very small hairline cracks and splits in the paper woofer cone of an RCA 515S2, or if I even need to bother with the repair at this juncture. They're all in the paper surround.

I bought this speaker on eBay recently, and had it shipped to me at my home (see the link here). The seller never mentioned the small splits, but then I doubt he even noticed them as they're so incredibly small, and the speaker was sold as-is. It would be wrong to try and return the speaker over such a small, and relatively easy to miss, flaw. Still, it is a bit irritating. Am I being unreasonably picky? I've been looking for a nice 515S2 for some time to setup a nice mono Hi-Fi for 78s and early Lps and 45s.

Is there any way to make the repairs in the surround area without a full recone? My go-to approach has usually been very dilute Elmer's glue or a small bit of clear nail polish, but the surround is kind of a tricky area of the cone to get a decent repair. I have yet to connect the speaker to an amplifier to check and see if it sounds alright; I had a procedure done Tuesday morning so I'm still not moving around too great. If it sounds OK, would I be better off simply leaving the speaker alone? Any advice would be much appreciated.

Attached are photographs of the speaker.


Attachments:
File comment: Full speaker.
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20190504_114317.jpg [ 115.71 KiB | Viewed 919 times ]
File comment: Close up of split.
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20190503_162236.jpg [ 96.04 KiB | Viewed 919 times ]
File comment: Close up of another split.
20190503_162224.jpg
20190503_162224.jpg [ 101.57 KiB | Viewed 919 times ]
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 Post subject: Re: Small tears in RCA 515S2 woofer cone. Best way to repair
PostPosted: May Sat 04, 2019 5:17 pm 
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Joined: Apr Sun 23, 2017 11:22 pm
Posts: 508
Location: 44035 (Near Cleveland Ohio)
I can't see the cracks/splits you're talking about, and I'm looking for them on a 30" desktop monitor. Maybe you could point them out? It looks like a decent speaker to me.

Dan


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 Post subject: Re: Small tears in RCA 515S2 woofer cone. Best way to repair
PostPosted: May Sat 04, 2019 9:13 pm 
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Location: 44035 (Near Cleveland Ohio)
One other issue with that speaker - - - before you test it, make sure the crossover cap is good, or has been recently replaced. Although the tweeter v/coil is pretty robust on these, too much low frequency sound can fry them, or at least warp them. You'll end up with a "buzzer" instead of a "tweeter". Not many folks know how to repair them correctly anymore either.

Dan


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 Post subject: Re: Small tears in RCA 515S2 woofer cone. Best way to repair
PostPosted: May Sat 04, 2019 9:24 pm 
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Joined: Apr Tue 17, 2012 7:58 pm
Posts: 114
Location: Metamora MI, 48455
I tested the speaker very quickly on a crummy little 2 or 3 watt chip-amp. The impedance match was poor which killed the what little bass it can produce outside of a good bass-reflex enclosure. It sounds just fine in my rather poor, quick test. Still, the bass coil and tweeter coils are both intact and both cones are moving properly. I had forgotten just how little cone excursion these extremely sensitive speakers from the 1940s and 1950s have; there's no way those splits are going to get any worse at my normal listening levels, which would likely be << 5 watts.

I'll get the crossover capacitor changed out tomorrow and start cutting plywood for a proper enclosure once I'm all healed up. I think I was overthinking the little splits and hairline cracks in the surround. That said, I have some good photographs of them I'll post later once my cellphone is recharged.

Here's a bit of Les Brown (https://www.youtube.com/watch?v=Uos9YC_Sp44)
Some Glenn Miller (https://www.youtube.com/watch?v=XLIBdOPebRs)
And finally a quick frequency check (https://www.youtube.com/watch?v=tMHvM_q56VA)


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 Post subject: Re: Small tears in RCA 515S2 woofer cone. Best way to repair
PostPosted: May Sat 04, 2019 10:00 pm 
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Location: 44035 (Near Cleveland Ohio)
You probably already are familiar with this, but if you're looking for a correct cabinet for this speaker, David B. Weems wrote "the Bible" on cabinet design. I read every article he wrote for Popular Electronics magazine in the 60's and 70's, and built a few as well. Your RCA probably has a resonance at 40-50 hz. or so, and cabinet/port design is crucial. I believe he published a book or two; the stuff I built was featured in the magazine.

Many moons ago, I engineered in a 1950's recording/motion picture studio - - all RCA equipment - - and we used LC1A monitors. I've never heard anything since that compared.

FWIW, I built a couple of Klipsch-style enclosures years ago, and recessed them into the space under a stairwell, so they took up no real estate in the room. Kinda limits the placement, but sure makes the wife less angry about having refrigerator-sized speakers in the living room . . . .

Good luck with your project. It'll be worth it.

Dan


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 Post subject: Re: Small tears in RCA 515S2 woofer cone. Best way to repair
PostPosted: May Sun 05, 2019 4:28 am 
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Joined: Apr Tue 17, 2012 7:58 pm
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Location: Metamora MI, 48455
My current intention is to build the big 6 to 8 cubic foot bass reflex enclosure recommended by Harry Olson, who incidentally, designed a series of amplifiers as well as the drivers as part of a complete, well matched system.

I'd love to find a single LC-1A to eventually transplant into the enclosure I build for the 515S2, as I've heard a nice LC-1A. That said, the 515S1 and 515S2 give a great deal of the same magic found with the LC-1A at a small fraction of the cost. In my case ~16% of the typical going rate of the LC-1A.

I may well eventually pony up $1500 for the better driver, but for now I'm content with the cheaper cousin.


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 Post subject: Re: Small tears in RCA 515S2 woofer cone. Best way to repair
PostPosted: May Wed 08, 2019 1:24 am 
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I'd personally spend the dollars on a new hearing aid, but some people are blessed with good ears. :lol:
2 feet square by 2 feet deep would make 8 cubic feet, so not massive, but a good sized speaker. Sounds like fun.

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 Post subject: Re: Small tears in RCA 515S2 woofer cone. Best way to repair
PostPosted: May Wed 08, 2019 2:13 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Seattle WA US
2x2x2 is just asking for resonances, yielding uneven response.
How about 4x2x1 or better yet three non-integers that multiply to 8.

-Chuck


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 Post subject: Re: Small tears in RCA 515S2 woofer cone. Best way to repair
PostPosted: May Wed 08, 2019 7:33 pm 
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Joined: Apr Tue 17, 2012 7:58 pm
Posts: 114
Location: Metamora MI, 48455
K7MCG wrote:
2x2x2 is just asking for resonances, yielding uneven response.
How about 4x2x1 or better yet three non-integers that multiply to 8.

-Chuck


That's in essence how I usually design a ported box. Avoiding setting up standing waves is paramount to get a reasonably flat frequency response. Then find the area of the port using the TS parameters of the driver.

For interior dimensions and a desired volume, I take and find the total desired enclosed volume in cubic inches, and then find values for length, width, and height that are not equal to 12n, where n is any positive integer, and where no two interior dimensions are equal. For an 8 cubic foot box, 16 inches by 27 by 32 inches should be adequate. It's also not a terrible idea to keep all dimensions > 12 inches just to keep the size and shape reasonable.


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 Post subject: Re: Small tears in RCA 515S2 woofer cone. Best way to repair
PostPosted: May Wed 08, 2019 8:44 pm 
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Joined: Apr Tue 17, 2012 7:58 pm
Posts: 114
Location: Metamora MI, 48455
A decent compromise for a 6 foot box would be 21 inches by 16 inches by 31 inches. It's only ~0.463% too large.


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 Post subject: Re: Small tears in RCA 515S2 woofer cone. Best way to repair
PostPosted: May Fri 10, 2019 7:48 pm 
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Location: Thornhill, Ontario, Canada
benman94 wrote:
... I'm looking for advice on the best possible method of repairing about a half-dozen very small hairline cracks and splits in the paper woofer cone of an RCA 515S2, or if I even need to bother with the repair at this juncture. They're all in the paper surround.
I see no splits. If there are any this small just run a thin coat of school glue over them... no need for paper patches.
I would also check that the spider or other VC support is still properly connected to the cone. I have a speaker that was disconnected here and rattled badly. A bead of glue carefully applied on the inside of the cone fixed it. Speaker is still in use.
Cheers,
Roger

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Ontario Vintage Radio Assoc. http://www.ovra.ca


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 Post subject: Re: Small tears in RCA 515S2 woofer cone. Best way to repair
PostPosted: May Sat 11, 2019 3:37 am 
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The speaker is destined for an enclosure of which it will be acting like a piston more or less. Such air compression forces may continue the deterioration of the surround.

I suggest shopping on line various speaker supply shops for a polymer elastic compound that is applied to the surround and about a 1/2" down the cone. The material remains soft and pliable for a long time as well as distributing forces of pneumatic compression. That will move replacement of the surround much further into the future.

Never use a glue that hardens or is not intended for speaker suspensions.

YMMV

Chas

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 Post subject: Re: Small tears in RCA 515S2 woofer cone. Best way to repair
PostPosted: Jun Thu 06, 2019 2:46 pm 
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Elmer's school glue.

It's made for paper and the cone is paper.

Just use a very thin bead over the cracks.


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