LEGACY AUDIO V System

It would be a mistake to think that the Wavelet is a digital room correction device – it is only a fraction of what it does. In essence, this engine is there to uncover the naked program material (music) as it was encoded on a disk or in a file by ultra-precise alignment of drivers in frequency and phase, and by reducing the impact of the room, especially the reflected sound and phase shifts are heard as colorations. In the abbreviated excerpts, taken from The Absolute Sound interview, Bill Dudleston explains the concept.

On the tweeters: The outside edges [of the tweeters] were brought forward in increments, allowing the ribbons to crossfire. 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.

On the dipole: The primary reason [to use it] 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.

On the crossover parts: 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, which is reducing amplifier headroom.

On the time corrections: It’s all in the timing. The sound of music is created by varying air pressure over time. Ironically, it is in the time domain that we find the real solution to the problem. It is the combining of multiple arrivals that cause problematic response dips and peaks. The room is dominating the decay of power. As a result the anechoic “flat” speaker may exhibit boominess or muddiness, and transient hangover. Attempting to equalize the response without regard to the time domain will actually compound the response errors at other points in the room while creating new time domain errors at the listener position.

 [The Legacy] algorithm relies on psychoacoustic weighting (how we hear) and how the sound sequentially arrives to us. The applied correction is not sensitive to position. Transient behavior is improved on- and off-axis. The measurements [by microphone] are exported to a dedicated website where a super-computer performs many thousands of iterative calculations to determine the optimal correction solution. After the correction algorithm coefficients are rendered for each speaker and automatically downloaded into the processor, the processor can apply the correction in real-time over a full 40ms window. Psychoacoustic weighting is emphasized in the calculations. The time domain is not compromised to fill minor dips in the response curve. The time-corrected response is always smoother but never ruler-flat. The bass will be deeper with faster decay. Vocals will be full, but not chesty or weak from the floor bump and dip that nearly always occurs. Sonically this translates to a more natural transient. If an actual drum is struck, the initial sharp transient pulse will be felt as well as heard. Conventional speakers without controlled directivity and proper room correction can smear the event in time, compromising tautness. This is readily evidenced by defeating the room correction, even on the highly controlled V system.

On the frequency corrections: We have learned that notch filtering of resonances is not a solution. When a dip is boosted in the power response, so is the reflection that caused the dip in the first place. Amplifier power is wasted, the speaker works harder, and the time domain is corrupted. Many of the nulls and buildups we experience are not from resonances at all, but instead from reflections interfering with the direct path to the listener. Remember that multiple reflections are required to create a resonance, so the time required for them to generate is significantly longer. Resonance and reflection behavior is quite different and should be treated accordingly. Automated equalization of the power response is treating a symptom, not the cause.

A chief problem in correction systems lies in the unevenness of sound throughout the room. It originates because of the way correction systems treat the different resonant phenomena within the room. They tend to disregard the origin of the resonance, treating them all in an equal manner. This is a mistake because resonances with different origins have radically different behavior.  The Bohmer method captures the wavefront as it is building in time. It collects a more useful and accurate sample over a longer period and distinguishes between direct sound, reflections, early resonances, and later resonances.