Rememer these...?

Crossover Capacitor Life... anyone?

Hi all,

I recently borrowed a pair of Celestion SL-600's that had been sitting unused in a friend's closet, and from what I am hearing, the speakers seem much brighter than I remember....

The Celestion SL-6, SL-600 was developed for Celestion by Graham Bank Ph.D, who after leaving Celestion, went on to NHT, where he most recently developed the Balanced Mode Radiator (BMR) a breakthrough in flat panel driver design now being implemented primarily in automobile (Toyota) and guitar amplification systems (LL. Bags). I have just learned that he presently offers consulting to speaker manufacturers worldwide through Cotswold Sound Systems Ltd.

Back to the legendary SL-600... it was the first (and possibly, last) speaker cabinet manufactured from Aerolam (an aluminum honeycomb laminate material). These speakers' driver design was also one of the first to benefit from the application of the then newly developed laser interferometry.

At the time these speakers were released in the mid '80s, they were favorites of mine. Due to their (unprofitably expensive to manufacture) non-resonant cabinet, the imaging and tonal accuracy they presented set a new standards. These speakers also featured a brick wall filter at 19kH to silence a resonant frequency generated by its copper dome tweeter.

Now my issue: as I remember, these speakers could never have been considered shrill. In fact these speakers did much in their day to make the early digital recordings and players listenable.

I wonder if the capacitors in the crossovers of these speakers have gone out of spec allowing the tweeter to "go postal." Does anyone have any ideas about the useful life of capacitors and other parts when used as part of this kind of filter network?

Thanks for your time.

for the music,
I can't comment on the caps going out of spec, but I believe that it was a notch filter, not a brick wall filter, in the SL600s, as the heavy, copper dome had its primary, oil can, resonance at the top of the audio range. The filter was deleted in the later, lighter, aluminum domes of the SL6S and SL700 that pushed the primary resonance further from the accepted audio range. The woofers were made of a proprietary plastic dubbed Cobex. The speakers were anything but bright, so if they are now, something has gone awry. Though the listening axis is higher than the other Celestions, an 18" stand being recommended, as opposed to the 24" stands of the 700 and SL6. It may be that the drivers do not sum correctly without ear height being above the tweeter. So this may be something to try.

IMHO although Richard Heyser's laser interferometry is often referred to as a "breakthrough" it certainly drew on prior art. In the '40s a flashlight and fan were used to study cone breakup modes in a very simplified way that clearly is conceptually related, yet infinitely more crude.