Carver ALS Line Source Loudspeaker System
- by Robert E. Greene
- Oct 29th, 2015
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.
The Adjustability of the Speaker
Typically, a loudspeaker review describes first a whole lot of things that, however much they may be wrapped up in poetic language and in the code words of audio, really amount to reviewing the frequency response in broadband terms, the overall balance. You know how the code goes: “detail” = excess top end, “transparent” = hole in the 100–300Hz range, “PRAT” (pace, rhythm, and timing) = extended but lowered in level bass, “involving” = midrange forward, and so on. This code system arose when people stopped knowing or caring what the actual frequency response was—and of course largely stopped measuring it. But they were still reviewing it, just in different words and forms of description. [See my review of the Magico Q7 Mk II in this issue. It has an identical frequency response to that of the original Q7, but a decidedly different tonal balance as well as significantly greater resolution and transparency. —RH]
Now comes a surprise! To a great extent, you will have to give the whole balance question a miss with the ALS because it has a very considerable range and a variety of adjustments. There are controls on the bass, the upper midrange, and the high frequencies, with marks to indicate Carver’s own preferred settings but no obligation to stick to them. The speakers are quite well behaved in in-room smoothness—actually rather more so than many quasi-point-source speakers, especially in floor interaction. The ALS starts with the advantages of good driver behavior and elimination of the floor reflection (and everyone has a floor!), but of course one can balance the speakers in different ways to suit room conditions and tastes—and with the Carvers, one can compensate for room character.
Still, three adjustments are not anywhere near enough to modify the response of a speaker to one’s sonic preferences. In my experience, I could not quite get the ALS to be entirely neutral-sounding (to my ears) using only the adjustments provided. Getting in there with an eq device and just going for it led to satisfying results beyond what the adjustments themselves allowed—and by “satisfying” I mean sounding tonally like what I have come to believe is on the recordings. Part of this may be that in my room I could not get the speakers quite as far from the sidewalls as I would have liked (more on this below). In any case, there were other things going on (a 300Hz prominence and the dip above that, for instance) that were not directly adjustable with the speaker’s controls, though those are very useful indeed.
In a sense, the speaker’s native, natural balance—and what Carver had in mind, as I understand it—is to have a BBC-style “Gundry dip” in the 2 to 4kHz range or on up somewhat further. (There are theoretical reasons why this sounds good—the ear’s diffuse-field response in this region is much lower than its frontal direct-arrival response, and making stereo recordings effectively moves some diffuse field into direct arrival. So it’s a good idea to compensate for this perceived difference. One can see the figures on this in Bech and Zacharov’s book Perceptual Audio Evaluation. But if you do not like this, you can adjust the extent of it, or even adjust it away with the controls, though I doubt you will want to as the speaker really “likes” the Gundry dip in sonic terms.)
Incidentally, the ALS is a natural for DSP room correction and eq adjustments in general, if you feel you want to make changes beyond the ones offered (of an analog sort). If you do want to DSP, you will be free of the restrictions many speakers of limited dynamic range impose. One can never fill in an infinite null, of course, but otherwise one can do essentially anything one likes here, thanks to the ALS’s enormous dynamic capacity. Also the speaker is quite high in sensitivity, so big dynamic swings do not require huge amplifier power. The pair played quite loudly (not DSP’d) with a moderate-power tube amplifier (20Wpc) that Carver supplied, though higher-power amplifiers, both solid-state (Sanders Magtech) and tube (Carver’s 350Wpc monoblocks) of course made them stand up and salute even more. However, DSP control of this type of speaker is not a simple matter; measurements of line sources are complicated because the whole interaction with the room is different, and the subtleties of what is “right”—already tricky for quasi-point-sources—are likely to be equally complicated and different. Fastening up some automated program is not likely to give good results (except in the very bottom end). You will need to adjust by ear.
So once you have adjusted the speakers to what you perceive as the most natural and neutral balance in your room, what then? (Further discussion will pertain to the speaker adjusted.)
The Listening Experience
First of all, one overwhelmingly obvious and compelling attribute is how pure and resolved the sound is, without being top-end aggressive. Then there is the ALS’s full bandwidth, all the way from subterranean lows on out to forever in the highs. There is unlimited dynamic capacity, for all practical purposes. And the distortion does not rise as the level goes up. The speaker just soars like an orchestra or a big band. Loud, but without any stress at all. (Really loud—the ALS is supposed to be able to produce 120dB+ levels cleanly, though I did not even begin to explore this.)
Another striking aspect about its overall purity is the lack of perceived intermodulation (and I imagine, measured intermodulation as well, though I did not actually measure this). Speaker manufacturers and testers tend to quote THD figures, but even more crucial is intermodulation in the extended sense. Does action in the trombone modulate the trumpet line? Does the cello section interfere with the violas? Do complex things turn to mush? With all too many speakers one has to answer yes to these questions. But here, not a bit. Everything stays clear and effortless and resolved in the true sense.
I think the speakers are very close to unique in this regard. I doubt that this effect can be maintained from the lowest to the very highest levels by any speaker except a large line source, and few of those will do it as well as this one. (I do not say that none can because there are the aforementioned Steinway Lyngdorf LS Concerts, for example. In fact everything I am aware of that is comparable in these aspects costs more. But the Eminent Technology 8Bs, which are quite inexpensive, also have very low perceived distortion, within a somewhat smaller dynamic range.)
The first thing I listened to seriously was a recording on which I play in the orchestra, Music from the Left Coast. The first piece here, Wayolo Lamoni by Christopher Tin, is a complex mix of orchestra, vocal solo, and choir (the famous Soweto Gospel Choir). Naturally I’m more than familiar with this recording. I was there playing and listening as it was made (to the playbacks as well as to the playing itself). The ALSes presented this piece in a startlingly realistic way, like a photograph with higher resolution but without any edginess, and the voices were dazzlingly beautiful. Carver himself, who had come to set up the speakers, seemed quite overpowered, and so was I. I had heard this recording a great many times, but never like this.
While the ALS did very well on every type of material, the vocal reproduction, both solo and choral, proved to be a particular strength, if one had to choose a single genre from all that these speakers reproduce so well. Reference Recordings’ A Gaelic Blessing (from the Rutter Requiem CD) was a marvel. And the solo vocalist on another CD in which I was playing was just gorgeous and truthful, too. My wife Paige’s reaction was, “ I really like her voice.” Indeed, and very much the real voice it was. This reaction was typical of people encountering the ALS for the first time. They noticed how good the music sounded without being distracted by how the speaker worked. To me, this seems to truly define naturalness.
While Carver was here, I also did a live-versus-canned comparison of my own playing recorded with a very nearly neutral microphone, where I played alongside the speaker channel where most of the violin is on that CD. This was really convincing, one of those exciting moments when one realizes anew that yes, audio really can work in terms of the convincing presence of a real instrument in size, physical scale, and unconstrained dynamics.
Turning to my orchestral stand-bys (the Dallas/Mata/Rachmaninoff Symphonic Dances, the Water Lily recordings), I found the recordings to be revealed in startlingly realistic detail. The inner complexities of scores, who was playing what, were laid bare in a way highly reminiscent of live orchestral sound. In the live experience, even when everyone is playing at once, one can still sort out all the sonics effortlessly and automatically. The famous cartoon of the frantic audiophile with the caption, “Crisis: the second oboe is too weak,” is a good joke. But in fact, in real life, one can hear the second oboe in correct balance and resolution. Many speakers jack up the top in an effort to get this sense of resolution. But the ALS has it by nature, without flinging any extra treble at you. Low intermodulation is the key, I think. In any case, the effect is very real. But the tonal character of familiar recordings was sometimes odd unless one had done some work to correct it.
Spatially, things were larger than usual. And one was also more enveloped in the sound, hearing more of the effect, so desired in concert hall design, of being immersed in the soundfield. These effects are a deliberate goal of the speaker design, as is having the image a little above ear level (which also happens). Whether you want these effects depends on your viewpoint. If you think of a stereo recording as an attempt to record information about space that will turn into the perception of space upon playback, then I think you’d have to count the ALS as enormously successful. If you think of stereo as aspiring to the condition of more or less anechoic playback with no time differentials introduced except those directly on the recording, then I suppose you had better look elsewhere. The ALS is different by design.
As noted, the position of centered solo instruments and voices was well focused. (Jim Smoak’s “Poor Man” from Arhoolie was very convincing, for one.) The time-delayed reflections and time differentials from the drivers on either side of the columns did not prevent the formation of stable center images, though the focus was not quite so precise as with more beamy speakers when you sit close to them. Whether this disturbs you or not is up to you. Spatially different the ALSs are—again by design.
Incidentally, during the rather long time I have had these speakers, a considerable number of people came by who liked music but were not audiophiles as such. Without exception, they really liked the ALSs and thought they sounded unusually natural. Most of my friends have heard a lot of stuff over the years coming by for visits. Audiophiles they are not, but experienced listeners they definitely are. The ALSs were a hit.
Usually at this point in my reviews, after describing all the good parts, I always start into the “and yet, and yet” nitpicking. But the case of the Carver ALS is different because this transducer seems to me to be an almost entirely successful realization of the designer’s vision. Moreover, they dodge completely many of the difficulties that arise in other line-source speakers. For example, because the driver arrangement, while unusual, is symmetric around the main (tweeter) axis, the problem of having to listen at one particular axis where mids and tweeters are correctly related does not arise. (This configuration problem is found in many line sources with a columns of tweeters and a single column of woofers.)
Still, there are some limitations that may also cause reservations. One obvious limitation might be the need for sufficient distance to each sidewall, an important factor because a great deal of sound is aimed at the sidewalls. Though Carver himself declared satisfaction with what he was hearing at my place, I wished that I had another foot or two on either side. (The room I was using is fairly large in total area, 27 feet long, but not wide, a little short of 14 feet.) This limited width almost certainly was behind the energy bulge at around 300Hz and the dip above (both could be adjusted out); these would have been much reduced or even nonexistent in a wider room. All speakers, of course, have response that depends on placement, but on the whole I think these speakers will give their absolute best in rooms at least 14 feet wide, preferably even wider. (Carver tells me that in future versions he intends to add a control to adjust the speaker for different room dimensions.)
Second, some people are going to worry about the adjustments and about the crossover boxes, but I think this concern is entirely unnecessary and misguided. All speakers with more than one driver per channel do signal processing and dividing. Just because you can see the devices doing it on the ALS, you should remember that it is always happening. In a lot of dynamic speakers, “the man behind the curtain” is inside the box. But the crossover functions are still going on. Moreover, anyone who tells you that some speaker will work perfectly in your room with no adjustments at all is almost surely, well, if not lying, exaggerating. Adjustments are a good thing! Really a good thing. That high-end audio has to some extent forgotten this is one of its greatest errors and weaknesses. (Recently, the tide seems to be turning with DSP adjustments. But analog adjustments, as in the ALS, have been useful all along. Don’t be like General Jack D. Ripper in Dr. Strangelove, obsessed with purity of essence, or in this case, purity of signal. He was, after all, crazy.)
Finally, there is the question of exact tonal character. One has to do some careful adjusting and perhaps some eq to get the ALS to match the tonal character of neutral stand-mount monitors or floorstanders. If this is a truly crucial point for you, then you might find a near-field monitor speaker and a very close listening position a more direct approach to addressing the issue. But you will lose the spatial scale and sense of scope of the ALS, and I think you will miss them.
The aforementioned points are really the only concerns involved in the way the ALS’ unusual design generates space—or even reveals recorded space. The differences among recordings remain; this is not some sort of surround processor with reverb that makes everything sound like it’s happening in a stadium. Far from it. The differences among recording venues are actually presented more vividly than usual. In this sense, space is not just being generated, but revealed. Still, the ALSs are different. They are supposed to be different. I think Carver would have been bitterly disappointed if at the end the ALSs sounded like ordinary speakers.
There are people who treat audio like those ancient religions where the same rituals are performed over and over in the hopes that if they are made absolutely perfectly, the gods will be appeased and the world will magically improve. I suppose that we all want audio to be as nearly perfect as possible, but to tell the truth, one can be skeptical about the idea that improving speakers in small and subtle ways will lead to revolutionary changes. In any case, Carver surely did not adopt that approach. The ALS is very well put together and things that are optimized are things that matter, but the main point is that this is not a microscopic improvement of things as they are, but a truly new departure, a way of generating stereo sound in a room that is qualitatively different from the forward-radiating, floorstanding, dynamic-driver boxes that have become the primary kind of speaker in audio.
The Carver ALS is a superb speaker on its own terms, which are quite different from those to which people are accustomed. Whether this is the speaker you want is not for me to say. But if you are interested—and in my opinion you surely should be—in a loudspeaker one of the most inventive and capable of all audio designers came up with when he decided to rethink the whole idea of how a speaker ought to work in a room to achieve the closest approach to actual music, you owe it to yourself to listen to the ALS. And rather surprisingly, for a speaker that is capable of not only such power and scale, but also of the most delicate finesse, perhaps you can actually afford to buy them.
As must be clear by now, I was startled and intrigued by the ALS’ realism in reproducing music, from the solo voice up to the largest orchestral recordings. Once everything was adjusted ideally (as already described), then coming back to these speakers after a full orchestral rehearsal or concert, I experienced surprisingly minimal discontinuity vis-à-vis the live experience. The motto of The Absolute Sound—“the sound of real music in real space”—was served very well, indeed, if in a distinctive way. I think my old friend and our colleague, the late Harry Pearson, would really have liked these speakers. I am certain he would have found them fascinating. And I have an idea of how he would have concluded a review of them had he had the chance to write one. In words he used on other occasions for things he considered revolutionary: “This must be heard by students of the audio arts.” I think so, too.
SPECS & PRICING
Type: Tower line source
Driver complement: Each tower contains 22 high-excursion 4″ drivers, 13 ribbon tweeters, one supertweeter, plus powered Sub Rosa subwoofer, electronic crossover to subwoofer, and adjustable passive crossovers for the main (tower) speakers
Frequency range: 18Hz to beyond audibility (main speakers to 80kHz)
Sensitivity (main speakers): 93dB @ 2.83 volts
Impedance (main speakers): 4 ohms
Rated max power: 1000 watts
SPL (two speakers): 118dB at 350Wpc
Minimum recommended power: 20 watts
Dimensions (exclusive of base plate): 4 5/8″ x 92″ x 6 7/8″
Weight: 120 lbs. per tower, including base plate
Price: $14,950 (including subwoofer)
BOB CARVER CORP.
1429 Ave D
Snohomish, WA 98290
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