Carver ALS Line Source Loudspeaker System

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Bob Carver ALS Line Source
Carver ALS Line Source Loudspeaker System

Bob Carver has had an almost unparalleled career as an audio designer. His Phase Linear amplifiers inaugurated the age of high-powered amplifiers decades ago. His Magnetic Field amplifier offered high power in a very compact package, and his later Sunfire designs again offered both exceptional power and high-end refinement. His original Amazing loudspeakers, which combined dipole woofers with a planar magnetic midtreble driver, redefined what was do-able for large-scale music, and did so at rational prices. His Carver Cube subwoofer ushered in the age of subwoofers that used very-high-powered amplification to produce deep bass from seemingly impossibly small enclosures. His Sonic Hologram was the first widely popular stereo-crosstalk device, presaging by decades current developments in this area (the propaganda for which largely avoids any mention of his accomplishment in this realm—such is audio). The list goes on and on of extraordinary accomplishments that combined ultra-high performance with fair pricing, with occasional excursions (the Silver Sevens) into the higher-price ranges. The ALS (Amazing Line Source) speaker system is Carver’s design magnum opus to date. One can well regard it as the summation of his remarkable career, a statement product that leverages the expertise of a lifetime of inspired design and profound thought about reproduction of music in the home, especially of large-scale music, which so often escapes small speakers.

People who are familiar with Carver’s design work over the years—which must be almost everyone—will realize that Carver doesn’t try just to make the same products as everyone else, only adding marginal improvements. Rather, he is an original thinker who reconsiders the philosophical underpinnings of every type of component he produces. The ALS is no exception. It represents the outcome of detailed investigation and deep thought about how a stereo can produce the maximum spatial effect in an actual listening room. To say that the results are remarkable and remarkably convincing would be to understate the case.

Moreover, this extraordinary speaker, the Amazing Line Source (ALS), is available at a price so low as to seem almost incredible. People are paying more than the cost of the ALS for little two-ways that offer nothing much except off-the-shelf drivers in supposedly exotic cabinets. One wonders a lot about people buying such things when for less money they could buy the ALS, with its ability to present the size and scope of music effortlessly and with ultra-low distortion. Even three-way floorstanders, however loudly they may play, are not really comparable in perceived “scope” (for lack of a better word ) in being able to sound as large music does sound.

This is not to suggest that the ALS offers only power and scale. In fact, it has a startling purity on small-scale music as well. If low distortion is one of the goals of speaker design—and, of course, it is—again, few are in the running with the ALS.

How the Speaker Works
As mentioned, Carver has rethought how speakers ought to work in actual rooms. So one needs to understand upfront that this is not just a jazzed-up version of a usual speaker, not a pimped-ride version, as it were, of conventional speakers. Audio people are sometimes a little worried about genuinely new ideas. They are somehow afraid that they will be sold a bill of goods, something that is peculiar but not really good. People like that can end up spending more and more money on things that are just like the things they had before, except more expensive (anyone in the market for a dynamic driver two-way for $85,000?). In this case, people like that might be too chicken-hearted to listen to the Carver ALS on its merits. But if you have an open mind and a vivid memory of what real music sounds like, then the ALS should find its way onto your very short list of speaker possibilities. (In fact, you can give it a listen and decide for yourself. There are dealers strategically placed in large cities, or you can visit Carver’s establishment—not such an unreasonable thing to do when spending this kind of money).

So how does it work? For a start, it is a line source. This is hardly an idea without precedent. Carver himself took this road in the original Amazing, Dali did the same with the Megalines, and then there is the recent Steinway Lyngdorf LS Concert (at a price!), in addition to Wisdom Audio, various large curved electrostatics that approximate line sources, several McIntosh models over the years, and so on. Many designers have observed that for effortless dynamic ease, line sources offer unique advantages, not to mention their elimination of floor and ceiling reflections.

The Carver ALSes do offer these usual advantages of line sources, but they are unusual, indeed unique as far as I know, in their choice of radiation pattern. The tweeter panels are arranged in a column and mounted on the front of it. But the bass/midrange drivers are positioned on the sides of the enclosure in two vertical columns, one facing to the left of the tweeter, the other to the right. The radiation pattern is thus by design very wide and makes active use of the walls. The idea is that the time-delayed reflections off the sidewalls (and with the speakers toed-in towards the listener, off the wall behind) will unmask spatial cues that otherwise would go unheard and unutilized in a conventional design that simply radiated the sound at the listener. But even more important in generating the sense of space is the time differentials among the drivers themselves, according to Carver.

As noted, the time differentials between the side-firing drivers (which are separated acoustically by the same distance as the ears are on either side of the head) and the forward-facing tweeters are supposed to act to enhance the sense of spaciousness. This is a complicated thing to explain in theory, but it apparently works. It is a familiar psychoacoustic fact that in that time differentials—and in particular time differentials that vary somewhat with the head’s angular position—act to generate a sense of space. (This is why headphones do not really image correctly even if binaural recordings are played—the sound does not change with head movements so that the ear/brain is unconvinced.) So it is perhaps not too surprising that lateral displacement of the drivers would have a spatial effect. But as far as I know Carver is the first person to exploit this deliberately (although it has occurred incidentally in other speakers, e.g. some of the McIntosh line-source models have mid-drivers on either side of the tweeter column, though not facing sideways).

Now, almost everyone has come to realize that some form of this idea of using sound that is not purely the direct arrival from a single source has a serious effect on spatial perception. In particular, as noted, sound off the walls can enhance the sense of space. But the non-line-source speakers of this type tend to lose much of the space they gain from wall reflections due to their floor reflections that send a “here I stand” message from the speaker to the ear/brain. The speaker is firmly located by the floor reflection even if the sidewall reflection turns out more or less ideally—which would happen only by accident in most cases. And of course in these designs there is not backwall reflection at all.

Carver approached this problem of revealing extra space head-on. In the process, he discovered (as already described) that the inter-driver time intervals were more vital than the wall reflections, contrary to what, say, the Toole school would lead one to believe. Carver says the space is “25 percent walls, 75 percent time differentials among the drivers.”

Indeed with the ALSes, space is revealed to an unusual, even almost unique extent. And this happens over a quite wide listening area, although the center position, or sweet spot, has magic as it always does. It’s well understood that an abundance of early reflections gets rid of the head-in-a-vise effect of anechoic stereo, or at least abates it to a huge extent. In the 1950s and early 1960s, this was taken for granted (by Villchur and Allison and many others), and it was assumed that people would listen in such a way that “power response”—total energy into the room as a function of frequency—was of vital importance because there would be so much room sound as part of the stereo experience. This question of how to use the room has been around for a very long time. But, to my knowledge, the explicit use of lateral inter-driver time delays seems to be a genuinely new idea.

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