Explain the advances in the new dual 4" AMT (Air-Motion Transformer) ribbons. What does this do to given aspects of the musical listening experience?
Dudleston: The 4" AMTs are capable of a more extended frequency range and slightly greater efficiency. The top end of the V system was given some pretty arduous requirements. Besides being sweet and non-fatiguing, while moving air 32 times more effectively than a 1" dome with the same diaphragm travel, it has to pass the “sit down/stand up” test for vertical coverage without combing issues. Next, it has to radiate over a 60-degree horizontal window without the top end dropping off, and lastly (most uniquely) it has to have greatly reduced level outside that angle across its range.
To pass the vertical test, the diaphragm height could not exceed 1". After months of ideas and experimentation, two 1" x 4" AMT drivers were butted end-to-end horizontally. We knew this could achieve the reduced levels off-axis as the array was larger than the longest wavelengths it would reproduce. Next, the outside edges were brought forward in increments, allowing the ribbons to crossfire. They were adjusted carefully to provide the desired window of coverage, the leftmost driver providing the highest-frequency coverage to the right extreme of the listening window, and vice versa. The center summation was quite solid, as it should be, but an added benefit was the mutual coupling at the lower end of the ribbons’ range, increasing efficiency and decreasing distortion even further. If the ribbons were not splayed as described, they would comb filter at higher frequencies. But because the diaphragm is moving away from the listener as it approaches the center, combing is not a problem. Ironically, the 6" drivers just below the ribbons intentionally rely on destructive interference off-axis to reduce their level.
Cordesman Assessment of Impact on Sound: I thought the simpler version of this driver in the Aeris was excellent, and it sounds even better in the Legacy V, although it is impossible to separate out the sound of this driver from that of midrange/midbass driver, the electronic crossover, and the other features in the Wavelet.
I’ve not always been a fan of AMTs, but this one is very, very good: tight, fast, and transparent with the natural life and air the best recordings provide. It competes directly with the finest competing ribbon, electrostatic, and dome tweeters I’ve heard, and the integration of the upper midrange and treble is exceptionally realistic and musical.
As I noted earlier, the combination of the AMT and other drivers in the Legacy V does an exceptional job of providing a wide listening area and natural soundstage on those recordings which have a natural soundstage. Upper-frequency performance was very good on test tones, and frequency response amplitude measured very well—far beyond the limits of my hearing.
What are the reasons for the dipoles?
Dudleston: The primary reason is as a steering mechanism. The technique provides better transient behavior and more snap. The goal is to reduce the angle of sound radiated in the room. The dipole by nature creates acoustic nulls to each side. It also radiates out-of-phase energy to the rear so that the rear reflections do not add constructively to the front radiation. In the midbass range the rarefaction of the dipole erodes the undesired bass leakage to the rear from the upper bass driver. As with microphones, an omni and a figure-of-eight combine to form the desired cardioid pattern, rejecting rear energy.
Cordesman Assessment of Impact on Sound: The sound in the lower frequencies is very good in transient detail and apparent speed, but I have no way to assess how much of this is due to the design features Bill Dudleston describes.
What is the musical rationale for large bass active and passive drivers and 1500 watts of power?
Dudleston: When one ponders the size of a kettledrum, double bass, tuba, or Hartke bass stack one can see why lots of piston area on a loudspeaker is important. Musically speaking, four times the air displacement is required for each musical octave lower in pitch. For a woofer to have a deep voice naturally, it must have a good amount of mass or very little damping. To have both a deep voice and good damping, a tremendous amount of power is required to overcome stiffness and inertia. The V system uses massive motor structures and weighted acoustically coupled radiators to accomplish the needed damping and deep tuning without adding port turbulence at high levels.
Cordesman Assessment of Impact on Sound: If you wonder if high power, large driver size, the right crossover, and the right cabinet really count with room correction to sharply reduce room-caused peaks and valleys in the bass, just try the Legacy V out with really deep test tones, synthesizer, bass guitar, etc.
The combination of large multiple drivers and plenty of amplifier power really pays off. The control of resonant peaks made possible by room-processing features described shortly also means you hear far more of the deep to upper bass in the way the signal is meant to be heard, and not the usual mix of peaks in the more audible portions of the midbass, and suck-outs in the upper bass or lower midrange. There also are fewer problems with audible room resonance and vibrating objects sensitive to the particular bass peak in a given room. Great for those few organ records that go really deep.
What are the advantages of an electronic crossover?
Dudleston: Generally, improved resolution and transient response are the most obvious benefits of connecting a speaker driver directly to the power amplifier. Component losses are eliminated, and crossovers are much more precise.
Even with the best quality passive components, there is a small degradation of sound for every component you put between the power amplifier and the speaker driver. Even a simple inductor adds resistance. The real benefit of eliminating passive crossover is that the passive filters are impedance-dependent by nature. To compensate for impedance variations, power is dumped to ground, reducing amplifier headroom.
With a DSP-based crossover it is possible to add as many stages or filters as required without accumulating losses. You have a vastly superior toolbox available to improve a driver’s response, align it in time, and create truly complementary crossover slopes throughout the system.
There are some important advantages that digital can hold over analog methods that are worthy to note. The obvious one is that the signal can be compensated in the time domain with surplus dynamic headroom. But there is also an overlooked advantage. When there is a multitude of complex theoretical correction blocks for the loudspeaker, crossover, room, apodizing filter, and low-frequency crosstalk, the powerful elegance of simply inserting the computed coefficients into a single algorithm without multiple circuit stages via DSP really pays off. With the Wavelet, except when you are using the analog inputs, you won’t even be introducing an additional conversion stage. Not only did you not add more circuit stages to accomplish this, you actually eliminated the weakest components in the signal path: the passive components of the crossover.
Cordesman Assessment of Impact on Sound: I can only agree in theory. I have no idea what a Legacy V with a traditional crossover would sound like.