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.

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

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

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)

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

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.

I'd personally spend the dollars on a new hearing aid, but some people are blessed with good ears.
2 feet square by 2 feet deep would make 8 cubic feet, so not massive, but a good sized speaker. Sounds like fun.

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.

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.

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

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

Elmer's school glue.

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

Just use a very thin bead over the cracks.