Sound-Lab A-1 electrostatic loudspeaker Dr. West investigates
Sidebar 2: Dr. West investigates
Roger agreed that it was possible that there was a problem with the HF transformers and promised to investigate the matter in detail. He called about a week later to explain that it wasn't the HF transformers after all, but that Dupont Mylar of improper thickness had been used to construct my pair of A-1s. Apparently, this Mylar had been cut from a fresh batch that had just come in and which was discovered to be about 6µm thick instead of 3µm, the diaphragm's increased mass thus explaining the HF droop. It failed, however, to explain the response change in the lower treble wrought by the new interfaces.
The implications of all this hit me squarely in the face. First of all, how could such a blunder have been allowed to leave the factory? Common sense dictates that, as a final quality-control check for a speaker of such lofty price and pedigree, a frequency sweep be run at the factory prior to shipment. The resultant response would easily identify problems with transformers and Mylar. If it's possible to generate individual response curves for $1000 phono cartridges, why not for $10,000 loudspeakers? That Sound-Lab has now apparently beefed up its quality control is small consolation to past Sound-Lab customers who may have been inadvertently zapped.
Second, that distant concert-hall perspective I had experienced with this pair of A-1s could, in hindsight, be seen as a direct consequence of the limited HF response. I clearly did not mind this sonic aspect of the A-1, which made it more polite and forgiving with many hot recordings. But I absolutely could not put up with the lower-treble disease that the new interfaces inflicted on the sound. So I shut down the Reference Room until the next chapter rolled around.
Dr. West returns: It took about a month for Sound-Lab to procure Mylar of the proper thickness and construct a new pair of A-1s for me. Roger arrived in April 1992 with a brand-new package, including new interfaces. These had been modified yet againmainly, I was told, to improve sensitivity by about 3dB. Another welcome design wrinkle had to do with the casters. Gone were the wobbly rollers that I'd always suspected of detracting from bass definition. Instead, the speakers were outfitted with TipToe-like feet, available as an option from the factory. Before he left, I asked Roger to assure himself that all was well with the speakers and that they met spec. This he did.
It was immediately obvious that there was a lot more treble. Not only was the lower-treble tonality now correct, but there was much more air through the extreme treble. In the weeks that followed, I assured myself that the magic was back. In fact, the A-1s now sounded better than they ever had. They were slightly more forward in presentation, bass control was improved, and, incredible as it may seem, the bass appeared to reach deeper than before. Yet this second time around, more than ever before, I became focused on and frustrated by this speaker's hangups at the frequency extremes.
Already insensitive to begin with, the A-1 is further handicapped at altitude by having to have its bias voltage cranked down to eliminate annoying crackling noises. This makes it even more difficult for power amps to provide adequate dynamic headroom. Bass transients didn't present a problemprovided that playback volume stayed at only moderately loud levels. At loud volume levels, either the amp would clip, or, with adequate power reserve, extraneous noise such as cracking and crackling would accompany program peaks. In the treble, I discovered that program material with lots of lower-treble energy would drive amps into gross distortion at even moderate playback levels; one amp simply blew up. This was something I had not experienced before. Why was every amp in the house suddenly going bonkers?Dick Olsher