Carver Amazing Loudspeaker (Platinum Edition) Page 3
It was this sort of experience that led J. Gordon Holt (footnote 2) to embrace the "Down with Flat!" philosophy in earlier issues of the magazine. It was quite puzzling at the time. Jack Hjelm from Audio Research had just finished installing some gigantic tube amplifier in JGH's system to drive one of the Infinity IRS systems (footnote 3). As a final touch he proceeded to equalize the speakers to flat at the listening position using an Ivie hand-held real-time spectrum analyzer. The resultant sound was bright; but, according to Jack, it had to be right; after all, it was flat. Well, sometimes "flat" is not. As soon as the ARC sage left, JGH proceeded to kill the treble.
You should now understand why some argue that the ideal transducer should have constant directivity up to about 5kHz, and decreasing directivity beyond—precisely the opposite sort of behavior exhibited by most loudspeakers. Such a directivity pattern will ensure that the direct/reverberant ratio of sound in the room is fairly constant as a function of frequency. Incidentally, the new Quad ESL-63, as far as I know, has the most uniform directivity of any commercial loudspeaker. The Quad's diaphragm is driven by concentric ring stators with suitable time delay such that the radiation pattern closely resembles that of a point source located some 300mm behind the diaphragm. Most other dipoles start off correctly with a controlled directivity in the bass, but cannot maintain that level of polar response with increasing frequency.
The electronic control box
The Amazing's optional gadget box allows a variety of signal processing. It may be inserted into the tape-monitor loop of an integrated amp or between power amp and preamp. Because the initial intent was to market the Electronic Controller as an integral part of the Platinum Series package, I received one with my first sample of the speaker.
Moving from left to right on the front panel, the first function is the bass Q control. Q can be adjusted from 0.3 to 2.0. Why anyone would want to loosen the bass any further is beyond me, but going the other way, to a Q of about 0.5, proved a worthwhile enhancement. At this setting, the bass character of the Amazing underwent a much-needed transformation in definition, from quivering Jello to reasonable firmness. Pitch definition and bass detail were now much more readily resolvable. It was no longer safe to eat beans while listening to music.
Unfortunately, there's a significant price to pay. The EC box not only squashes dynamics but contributes an earful of solid-state hardness and grain to the mids and treble. The cure in this case is worse than the disease. With the EC in the chain, tube amps sounded solid-state, tube liquidity being well masked. Removal of the EC from the signal path after an extended listen invariably brought forth a sigh of relief.
To the right of the bass Q control are a "High Frequency Trim" that allows you to shelve the treble above 4kHz, a "Sub Bass" synthesizer that will generate or supposedly "restore" sub-bass harmonics to program material deficient in deep-bass energy, a "Gundry Perspective" control that allows you to shelve the upper mids and thus change the apparent orchestral perspective, and finally a "Sonic Hologram" control.
The Sonic Hologram attempts to fix what some consider a basic flaw of conventional stereo. The argument runs something like this: When we listen to an instrument live, each ear receives a single input; call these left and right. Trying to reproduce the same solo instrument via a pair of loudspeakers results in each ear receiving two inputs. The left ear receives a left speaker input, and because of head diffraction there is delayed crosstalk from the right speaker. The situation is similar at the right ear. Sonic Holograpy tries to cancel out these crosstalk signals so that the left ear effectively hears only the left speaker, and vice versa. This sort of argument makes a lot of sense when trying to reproduce a binaural or "dummy head" recording via loudspeakers. Such a recording will only sound right through headphones, and there has been a lot of work done on devising circuits to make binaural recordings compatible with stereo loudspeaker reproduction. However, the logic of the argument breaks down for true-stereophonic recording techniques such as Blumlein. Here, as with other coincident recording techniques that rely on intensity differences for localization, it is precisely this kind of crosstalk generated by two-channel stereo that is relied on to produce natural phase cross-correlation between the ear-input signals. The important point is that head diffraction is operative at all times, generating two ear-input signals even under live listening conditions.
I did experiment with Carver's circuit and found it to make a difference, but only sometimes for the better. Although the action of the Sonic Hologram circuit seemed somewhat unpredictable, nevertheless a couple of generalizations are in order. First, the circuit acted to expand image outlines, providing a blown-up or zoom version of the original spatial outlines. Second, on multi-miked recordings, and in general where the left and right channels contain quite a bit of out-of-phase information, the Sonic Hologram helped to flesh out the soundstage—but at the expense of pinpoint imaging. However, program material recorded with coincident or quasi-coincident techniques, where there is high phase coherency between channels, was adversely affected by the Carver circuit. Here the imaging became unstable, outlines wandering away from their center of gravity within the soundstage. A case in point was my wife Lesley's voice throughout the Lesley Test. The weight of the image shifted from side to side as if an unseen hand was playing games with the channel-balance control.
On the whole, I'd forget about the Electronic Control Box.
Will the real Amazing please stand up?
As this project evolved, it became clear to me that the Amazing was truly a moving target, a fluid design that certainly from my perspective, and inferentially from Bob Carver's, was not altogether final. Santa Fe became a proving ground for the Amazing; several versions of the speaker have been assessed to date. I have to confess, however, that some of the changes along the way were triggered by my thoughts and suggestions. At times I felt as if I were in the design loop for this product. The above scenario is more than vaguely reminiscent of the Bud Fried syndrome: "I'll keep changing it till you're happy." And I'm sure that the initial monkey wrench thrown by Bob into the proceedings was an attempt to manipulate the situation in his favor. But I remain convinced that Bob was subsequently motivated by a passion to perfect the speaker to the detriment of good business practice. There's no question in my mind of Bob's intense commitment to the speaker.
To clarify the situation, let me give you a synopsis of the sequence of events. The first sample (which we received in July 1989), as you'll discover shortly, was beset by serious sonic problems and was on its way to, most probably, a terminal review. Just about then, in early September, as though he had read my mind, Bob phoned me and the fun and games started.
All of the above add up to unusual circumstances indeed. Normally, a manufacturer does not receive this much free consultation. From my perspective, it was a question of wanting to see a promising product succeed. From JA's perspective it was crucial to ensure that the magazine would not get trampled on—our policy is not to allow manufacturers to use Stereophile's facilities and Stereophile's writers' talents for design consultancy purposes, whether paid or unpaid. The ground rules, as JA laid them out, were that if Bob were to visit Santa Fe to redesign the Amazing Loudspeaker, Stereophile would report on all of our experiences with the product; that Carver would take full responsibility for the design; and that a production version of the speaker would be subsequently submitted for testing. It was this final item, however, that proved difficult to pin down. Apparently, the Platinum Edition Amazing Loudspeaker was being sold all along, so that at least some speakers—identical to my first sample—are either in dealers' inventories or in consumers' hands.
Sample 1, Take 1. Out of the box and before any significant break-in, the sound of the ribbon had a strong metallic flavor to it—as though a large sheet of Reynolds Wrap was being crinkled. After over 100 hours of break-in this coloration largely abated, but did not entirely disappear. There remained a metallic aftertaste, no doubt due to internal resonances in the presence region.
During setup, the recessed terminal cup of the Amazing proved a pain in the butt. It was difficult to fit spade lugs within the recess. However, it proved real easy to strip the plastic shaft of the binding posts provided; be careful not to overtighten these. Lord, why is it so difficult to find expensive loudspeakers with high-quality binding posts?! I also managed to work loose one of the binding-post retaining nuts, in the process breaking a solder joint. After Robert Harley had repaired the connection, I proceeded to tweak the installation.
It proved necessary to back off the front baffle a good 10' and toe-in the speakers considerably before a decent soundstage materialized. I next trimmed the tonal balance using the Upper Midrange Control (UMR). This pot allows a nominal ±3dB of amplitude control over a frequency range of 1–6kHz, with full impact at a center frequency of about 2.5kHz. This exercise turned out to be extremely frustrating. I spent hours trying to get the Amazing to sound right. Using the Lesley Test as program material, it was just impossible to obtain a natural balance. Turning this pot up to where Lesley's upper registers had the right brilliance also elicited sibilance and a metallic transient etch sufficient to tattoo my ears. Shelving the upper mids and presence region down to the point of achieving a tame enough presentation brought about a significant alteration of tonal colors. Rather than preserving a sweet and smooth character through the upper registers of soprano voice or violin overtones, timbres took on a slightly dry and grainy quality.
Footnote 2: In whose ears we trust.—John Atkinson
Footnote 3: See Stereophile, Vol.9 No.4, pp.29–41.—Dick Olsher