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The A-1's radiating surface area is 2200 square inches—a full 30% greater than the Model A-3's. When sound is radiated from such a large, tall surface in close proximity to both floor and ceiling, the vertical dispersion of the sound follows that of a line source. That is, a plane wave is launched from the surface for those frequencies whose wavelength is small compared to the length of the line source. Hence, all large panel radiators are generically referred to as planar speakers. In the nearfield of a line source there is no vertical dispersion of energy. Energy radiates in a figure-…
The main purpose of the panels is to enlarge the effective area of the speaker's baffle. As is well known, dipole radiators with a finite baffle size lose radiation output below a critical frequency due to front-to-back cancellation of sound energy. This critical frequency is determined by the average baffle dimension. Cancellation (at the rate of 6dB/octave) is effective for frequencies whose half-wavelength is larger than the average baffle dimension. At 50Hz, the half-wavelength is 11', so that dipole radiators must be large in size to maintain decent bass efficiency.
If the dipole…
With the A-1, not only the midrange but the bass and treble are covered by a single driver driven uniformly over its entire area. The resultant cohesiveness is most persuasive. The best way to appreciate this is to keep the music simple and focus on a solo voice or instrument.
Let's start with the lower octaves. Gary Karr's rendition of the Adagio d'Albinoni (King K33Y 236) on double bass, while technically imperfect in spots [Mr. Karr manages to play out of tune, is what DO is trying to say here.—Ed.] is blessed with an astonishingly sympathetic acoustic space. The grandeur of the…
Sidebar 1: DO measures
Several days after I'd powered down my word processor, Roger West called to inform me that the A-1's electronic interface had been modified to provide increased flexibility in contouring their bass response. Independent shelving of the lower midrange and bass was now possible in steps of 3dB. The response below 100Hz and the range between about 100 and 600Hz could now be adjusted separately for more precise handling of the speaker/room interface. Roger also mentioned a new toy he called "SALLIE"—Sonic Attenuation for Lower Levels of Interference Effects (known more…
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…
Sidebar 3: DO's last wing fling
I wish I had a dollar for every time I've removed or installed these gigantic wings. During his visit last March, Roger West suggested that I try the wings mounted to the front of the speaker. So I went at it again. There's considerable logic to flip-flopping the wings to the front. This avoids creating a resonant cavity with the side and rear walls, and thus, in principle, should help alleviate the boxy character that rear-mounting the wings caused in my room. Second, it makes more sense to "horn-load" the front wave rather than the back wave. Dispersion…
Sidebar 4: Specifications
Description: Full-range, transformer-coupled, electrostatic loudspeaker. Frequency range: 28Hz to beyond 20kHz. Nominal impedance: 8 ohms. Sensitivity: equivalent to 88dB/1W/1m at 4m. Minimum amplifier power: 100W. Maximum music power: 450W. Bias power-supply input: 117/220 VAC, 50/60Hz.
Dimensions: 81.24" H by 35.5" W by 10.5" D (panel), 25" D (base). Weight: 185 lbs each.
Price: $10,950/pair in standard wood finish (1992). Accessories: "Acoustic Wave Delay Panels" (wings), $1242/set of 4 in oak, $1566/set of 4 in walnut; "SALLIE" BWA-1 Back Wave…
Sidebar 5: Review System
The Sound-Labs require a high-powered amplifier. Not to worry: the A-1s can soak up several hundred watts of music program without any concern for their physical safety. Because of the requirement for large voltage swings, a tube amplifier makes much more sense than a solid-state design's fairly low voltage rails. Despite JGH's current love affair with the Boulder 500, I would think that a 200Wpc tube amp would make a more optimal partner. I've experimented with a variety of amps over the past six months. The rising impedance characteristic of the A-1 in the bass…
Sidebar 6: Measurements
To investigate the answer to Dick's question, I measured the A-1's impedance magnitude at three settings of the Brilliance Control (BC) with DRA Labs' MLSSA system. With the BC set at Maximum (pot wide open), I obtained the curves in fig.1. Although the magnitude of the impedance is above 10 ohms from the upper bass to 2kHz, and well above 30 ohms in the bass, note the drop in the mid-treble and above. The cursor indicates a punishingly low 1.3 ohms at 20kHz with an equally punishing phase angle of –75.5°, dropping even further to just a small fraction of an ohm at…
Stereophile's owner, Source Interlink Media (SIM), announced today that it is merging the two most powerful print and online media brands in the home technology field, Home Theater and Sound & Vision, to create a single powerhouse consumer brand dedicated to electronic entertainment.
SIM executives joined these two brands under the Sound & Vision banner because of the undeniably quick evolution of home and portable electronics products. Sales of new audio/video components like soundbars, wireless speakers, high-performance headphones, and computer audio gear have virtually…