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Audax HD-3P Piezo tweeter
Peter Comeau explains how to update your World Audio Design KLS3 loudspeakers, if you too have suffered the dreaded 'Gold Dome Wrinkles'...
from Hi-Fi World JUNE 08 issue
Since I updated a reader’s KLS10 Gold bookshelf speakers last year I’ve had more than a few e-mails asking whether the SEAS Millennium treble units I installed in place of the gradually declining Audax HD-3P Piezo units could be used in the KLS3 Gold as well.
Whilst the simple answer is ‘yes’ I pointed out that a crossover change would also be needed, particularly for the treble unit crossover and possibly, also to the midrange crossover to perform a perfect match.
This dismayed all but one correspondent who was so eager to refurbish his KLS3 Gold MkIIs that he delivered them to the World Designs Lab so that I could perform the necessary measurements and revise the crossover.
Audax Gold Dome wrinkles
First, a little bit of background on the problems suffered by the original KLS Gold Audax HD-3P treble units. These work by utilising the piezo effect on a gold sputtered film held in an elliptical dome shape by a pressurised chamber filled with Nitrogen.
Early units suffered from a less than perfect gas seal which causes the Nitrogen to gradually leak away. The first visible sign of this is that, in high pressure (fine) weather, wrinkles or creases appear in the gold dome. The audible effect is of a loss of sparkle and ‘air’ to the sound but, because the loss of pressure is gradual over a long period, the listener may not be aware of the treble loss.
Nevertheless the treble loss is there and, eventually, you’ll need to take action to restore your KLS Golds to their former audible glory. Now, not every Audax HD-3P treble unit suffers in this way. As soon as Audax became aware of the defect the seal was redesigned with the result that later domes will hold their gas pressure. The test is simply to see whether the wrinkles in the dome appear, particularly when atmospheric pressure is high. If not, leave well alone.
When the speakers to be modified turned up at World Designs the problem, in one of the units, was very pronounced and, indeed, treble output was severely curtailed to the point where the speakers were unusable.
Replacing the units with the SEAS Millennium T25CF002 was, physically, not quite so straightforward as it had been with the KLS10 Golds. Because of the close proximity of the midrange and treble units, and the larger outer diameter of the SEAS faceplate, the treble unit has to be moved upwards towards the top of the cabinet. Luckily there is enough room, just, to fit the new treble unit without it overlapping the top of the cabinet!
All that is necessary is to take a file, wood rasp, or preferably router, to the treble unit hole and elongate it to accommodate the magnet and terminals of the SEAS Millennium. In this particular pair of speakers we also took advantage of using a router by recessing the drive units into the speaker baffles. This isn’t necessary for the upgrade but does provide a slightly smoother frequency response as there are no close proximity drive unit edges and steps down to the baffle to cause extra diffraction and interference effects.
Anyway, back to fitting the new treble unit. As I said the SEAS faceplate is larger in diameter than the Audax, at 110mm, so making new fixing screw holes isn’t a problem and it won’t look as though you’ve butchered your cabinet to fit the Millennium in place!