Hales Design Group Concept Five loudspeaker
"Let's face it," he confided, "six thousand dollars is a lot of money. You really ought to be able to buy superior performance for that. I have certain philosophies that I use throughout my designs: I believe in certain diaphragm properties, and I use the same crossover design—fourth-order Linkwitz-Reilly acoustic slopes—and the cabinet technology and bass-loading remain the same throughout the line. The Concept Five embodies all these design approaches in an affordable, reference-quality design."
It's hard to argue with that reasoning. In fact, it's hard to argue with Paul at all. He's an ebullient fellow—get him started and the words just tumble out. He's got strong opinions, and he gives 'em to you in torrents. But it's obvious from the way he marshals his arguments that he's not shooting from the hip—he's thought things through and, whether or not you agree with all he says, it's a pleasure to listen to a man who's so enthusiastic.
Take bass-reflex, for instance. All of Hales' designs employ critically damped sealed-box enclosures. He feels so strongly about this that Hales Design Group gives away coffee mugs emblazoned with the motto "Death Before Bass-Reflex."
"I think that bass-reflex is wrong. Moving-coil loudspeaker designers have spent the last decade addressing resonances within the system—and these days, even electrical designers are addressing resonances within preamplifiers and D/A converters. The harm that unwanted resonant energy does to any system is incontrovertible. To make a bass-reflex system, a designer has to intentionally build-in a secondary resonance—and if that weren't bad enough, they excite it on purpose to augment the bass energy of the speaker. I don't see how any speaker designer with a clear conscience can brace his cabinet, use rigid cones and domes, and apply damping material throughout the cabinet in order to reduce resonance—and then choose to design a resonance into it. You can hear that the bulk of the lowest frequencies reproduced are ill-defined and resonant in nature. It just isn't right."
I was exposed to an intense barrage of the Gospel according to Paul when Hales and Scott Brooks, HDG's Marketing Director, arrived in Santa Fe to meet with the Stereophile gang and set up a pair of Concept Fives in my listening room. We get letters from readers complaining that, in the real world, speaker designers don't drop in to set up their designs. There's some validity to this argument, although anyone spending six large should get all the placement assistance they could ever want from their dealer. Most of the time, however, these visits are kind of an ordeal—at least at first. Mr. Manufacturer is trying to assure himself that he's going to get a fair shake from Mr. Reviewer, and Mr. Reviewer—at least this one—feels like his setup technique and methodology are being scrutinized with Talmudic intensity.
If both parties are lucky, everybody calms down after a couple of hours and the occasion degenerates (elevates?) into a BS session and listening party. This is, in fact, what happened with alacrity upon Paul and Scott's visit chez Wez. After a few hours with the Fives, mostly spent listening to Paul, I knew that the Concept Five was going to be fascinating. Little did I realize that it was going to take me on a journey to the heart of music.
Q: Is that a musical instrument?
The Concept Five is a floorstanding three-way speaker that stands 48" tall, but its 12" width gives it a slender, unprepossessing mein—despite its 21" depth. The baffle slopes back at a severe rake mirrored by the back panel—you've seen the general look before in the Avalon family of loudspeakers. The 3"--thick baffle is cast from a gypsum-based cement that has been augmented by substantial amounts of a glass-fiber reinforcement to add tensile strength. This is analogous to adding re-bar to a cement foundation—cementlike materials tend to have impressive compressive strength, but aren't all that strong in the tensile dimension. The baffle is molded to eliminate diffraction distortion, the top and edges curving smoothly to meet the sides of the cabinet.
Hales considers the baffle essential to achieving the sound he's looking for. "Elimination of resonance is critical to achieving low coloration, and the greatest amount of mechanical energy occurs at the front baffle. Since we mount the drivers to the baffle, we want it to be as physically rigid as possible. Just watch a tweeter playing: Its motions are so small that they can't even be detected by the naked eye, yet they produce the sound. Anything that distorts those microscopic motions—such as the motion of what the tweeter is mounted to—distorts the sound.
"Imagine someone holding the classified ads in front of you and wagging them back and forth—there's not a chance in hell that you could possibly read 'em. You might be able to read a 24-point headline on the front page, but not the want ads. That's what happens with the drivers in a flimsy baffle—the bass may not sound blurred because the motion is small relative to the wavelengths involved, but the tweeters can't cope with even small amounts of vibration because they reproduce such tiny waves to begin with. The cement baffle is our attempt to make the most inert, nonresonant platform in a cost-effective way—but it also allows us to do one additional thing. It allows us to shape the baffle in such a way as to virtually eliminate any diffraction that would give your ear a cue that there's a physical speaker there."
Sounds pretty simple, no? Just pour the compound into a mold, let it set, and voilà—you have one sixth of the cabinet. "That doesn't sound all that complicated, but I'm here to tell you that it was a huge undertaking to make it repeatable. It took a year to figure out the formulation and the curing times, not to mention figuring out ways to pour it in and then unmold it, while keeping it intact. Every baffle spends 72 hours curing in our two-story oven. All of that stuff, even the way we mix the cement, must be very carefully undertaken; mess up even one step of the process and it turns into a bunch of crap—as we have discovered on more than one occasion. Curing turned out to be unbelievably critical—97% of the strength is the result of the last 5% of the cure, so we had to develop an oven and a system that could take us to that point."
The rest of the cabinet is pretty straightforward. Staggered internal bracing, contrary to a commonly held belief, does not make the structure less resonant. Rather, it raises the pitch of the cabinet's resonant frequencies. At higher frequencies, Hales observes, the forces applied to the cabinet by the midrange and treble drivers become insignificant in relation to the mass of the enclosure. The cabinet is constructed of 1"-thick MDF, except for the top and rear panels, which are constructed from 2" MDF—other than the baffle, those tend to be the liveliest panels in a rectangular speaker.
The aluminum-dome tweeter, manufactured for HDG by VIFA in Denmark, features an underhung geometry in which the voice-coil is quite a bit shorter than the magnetic gap. This means, claims Hales, that "the tweeter never leaves the linear flux field during its operation, lowering distortion by a tremendous margin. That tweeter has a linear throw of !X1mm, which is unheard-of in a tweeter—that's more like a midrange-driver spec. The diaphragm is the standard VIFA, design but the suspension and the magnet assembly are ours."