Art Dudley Listening

I decided to rule out the gap once and for all by taking the original diaphragm, now presumed useless, and drilling out the offending alignment hole, apparently 1/8" in diameter, to 9/64", after which I carefully and slightly countersunk it. That provided just the slight amount of slop I needed—and what I now realized was a perfectly round former and coil of consistent and correct thickness dropped neatly into what I also now realized was a perfectly made voice-coil gap.

Whether the mounting pins on that Altec had always been a little bit off, or whether one or both had become distorted over time (There was a fight . . . ), I have no way of knowing. But when I carefully redrilled the GPA replacement diaphragm as I'd done to the dead original, it, too, fit perfectly—and now sounded, if anything, slightly better than that of the other Altec.

A lesson learned: Those who compare original and (various) replacement diaphragms and find that one or the other sounds too harsh may not be comparing diaphragms after all, but rather pin alignments. In any event, as long as one does so with caution and takes care to remove the detritus of drilling before attempting reinstallation, it seems to me the Altec owner can do no harm in giving him/herself a little wiggle room in the diaphragm department; the diaphragm's position can be microtweaked later, with or without the help of a high-frequency test tone, by loosening the diaphragm mounting-ring screws, moving the ring by very slight degrees, listening, and carefully retightening those screws.

Cheapo wine
The time had come to start dealing with those little screwdriver accidents.

On closer examination, both of the Altecs had the same number and type of wounds: one cone puncture each, both looking exactly as if caused by a Phillips-head screwdriver, and one surround tear each. Also, the cone of one 604E looked considerably dirtier, and the dirt looked as if it had, at one time, been liquid. (I pictured that driver, sitting on the curb, getting puddle-splashed by a passing cab.)

I dealt with the dirt first, doing so with the same approach I use for almost everything that's dirty and fragile: I put some hot water in a bowl—hotter than hot tap water, but not by much—and added to it a single small drop of dishwashing liquid. I then dipped a gauze pad in the water, tamped it off on another fresh gauze pad, and used that second pad to clean the cone's outer surface with very light radial motions. The amount of dirt that came away was astounding—I went through several pads—and the gauze left nothing of itself behind. In the end, I didn't get the cone entirely clean—going further would have required applying more pressure than seemed wise—but now it looks a lot better.

For now, the cone punctures don't trouble me: I doubt they have any effect on the Altec's audible performance, and they don't stand a chance of weakening the cone overall. I'll attend to them eventually, probably by filling them with polyvinyl glue-based papier-mâché. (A great tip from Steve Rowell of Vestal, New York retailer Audio Classics: when making such repairs, use pulp from an old, unrepairable speaker cone.) Unfortunately, unlike cone punctures, tears in the rubberized fabric surrounds of a 604's bass cone can affect the sound—and are even more likely to worsen over time. Those needed to be fixed without delay.

On past occasions I've replaced cone surrounds with equivalents of modern make (footnote 4), but I wanted to avoid doing so with these Altecs. For one thing, it's safe to assume that Altec used a jig of some sort to clamp the surround to its cone while waiting for the adhesive to set: the bonds appear far tighter and neater than those I've seen on contemporaneous products from Advent, AR, EPI, et al. Not only do I doubt my ability to effect such a neat, tight bond on a cone in situ, I seriously doubt my or anyone else's ability to cleanly remove all traces of the old surround and its adhesive from the edge of the cone prior to regluing—thus ensuring that any new bond would be compromised from the start. Also, I have no interest in compromising, any more than is strictly necessary, the originality of my Altec 604Es: for both sound and collectability, it's better to repair than replace.

I considered a number of alternatives, including bookbinder's tape (another great idea from Steve Rowell), before deciding to buy replacement fabric surrounds—not as replacements, but as a material I could cannibalize for patches. As for an adhesive, an Internet search turned up the ideal substance: BC-1 Black Rubber Adhesive, which Parts Express sells for $7.95 for a 1-oz bottle (footnote 5). The surrounds themselves were $39.95/pair from Simply Speakers (footnote 6). (Learn from my mistake and skip the extra-cost option that Simply Speakers refers to as their Edge Sealer kit: It's just more glue—and not the kind you need.)

The repair itself was straightforward. I began by spending about an hour on each 604E, inspecting every inch of its surround under an illuminated magnifier and carefully removing contaminants with a good pair of tweezers, all the while mindful of the Altec's very powerful magnets. Said crud included bits of tinfoil (!), something I'm sure was an insect casing (!!), and lots and lots of white dog hairs: As with so many other Altecs I've seen, the rubberized surrounds of these 604Es are enduringly pliant and sticky, especially on sunny days; one more reason audio-equipment manufacturers are always telling consumers to Keep this product away from direct sunlight!

With the surrounds as clean as I could reasonably and safely make them, I used a sharp hobbyist's knife to cut my patches, making sure they were larger than the tears they covered by at least 1/8" in every direction. (For the tear on one driver, I had to make sure the patch extended onto the outer lip of the cone itself.) Sparingly at first, I applied BC-1 to both the inner side of the patch and to the area surrounding the tear, then laid the patch with a pair of tweezers and pressed it in tightly with one of my favorite cheap, multipurpose tools: L-shaped "toothpicks" made of a Teflon-like nonstick plastic, from the luthier's supply company Stewart-MacDonald ($1.95/box of 50, footnote 7). After the adhesive dried, I applied BC-1 more liberally to the outside of the patch, taking care to blend the edges in with their surroundings. The completed repair is mechanically effective and hard to detect, if not quite invisible.

Have a good time
Eventually, I put the two Altec 604Es back where they were when I noticed the bum treble diaphragm: on the floor of my listening room, about 5' from each other, angled in and up toward my central listening seat, the size and shape of the 604 are such that, when placed on a flat, level surface, the cone naturally tilts upward.) I connected them to their outboard crossovers—another whole column right there!—and the crossovers to the outputs of my Shindo Haut-Brion stereo amplifier.

Obviously, low-frequency performance was curtailed by the dipole-cancellation effects of operating such a driver in free space, without a baffle. Nonetheless, it took me far less time than expected to acclimate to the lack of bass. Even under such ridiculous conditions, the 604E Duplexes were musically captivating—almost hypnotically involving—and surprisingly sonically accomplished. I remember listening to a stereo Aretha Franklin record and being startled at the way her voice was located dead-center, approximately 4' behind the drivers. This was very, very encouraging.

But, as I hinted earlier, the treble ranges of the two drivers didn't quite sound the same, one being silvery and the other actually somewhat golden. I confirmed this by swapping channels on both my preamp and amp, to make sure I wasn't attributing to the Altecs some anomaly elsewhere in my system; and since I heard the same difference with CDs and LPs, I didn't bother screwing around with my source components. Fresh advice from Early Bender—proprietor of vintage-audio specialty firm HiFiTown and son of the late, legendary Walt Bender—has encouraged me to try harder to bring the compression drivers of both drivers up to the same spec. I'll detail those efforts in a future column—and describe the 604-friendly cabinets I'll be building this summer. Stay tuned.

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4 See the May 2010 "Listening."

Footnote 5: See www.parts-express.com. Tel: (800) 338-0531.

Footnote 6: See www.simplyspeakers.com. Tel: (727) 571-1245.

Footnote 7: See www.stewmac.com. Tel: (800) 848-2273.