Wednesday, December 4, 2013
High-end Soundstages - Part 2
By the early 1970s both the electronic hardware and available software had evolved to a sufficient level of refinement where, along with sonic accuracy, a realistic psychoacoustic 3-dimensional soundstage was possible revealing not only a left-to-right presence but also remarkable front-to-back realism. However when trying to correlate technical measurements with a piece of equipment’s ability to recreate this realism, nothing consistently stood out. Something beyond current technical measurements seemed to be at play.
In 1979, Bob Carver founded the Phase Linear Corporation believing that one particular measurement - the integrity of the input phase compared to the output phase - contributed to this 3-D ability. He designed and built several amplifiers whose claim was that not only did they possess the usual low THD and IM distortion measurements but also linear input-to-output phase (no time smearing here folks). Time-aligned loudspeakers appeared reinforcing the belief that this may be the missing measurement to explain this 3-D ability. The term "sound stage" quickly caught on by reviewers to subjectively describe the height, width, and depth of this acoustic illusion.
Over time equipment reviewers discovered that combining different pieces of equipment achieved different results. For example, time aligned speakers played through time-aligned amplifiers did not achieve a deep-wide-high sound stage and detailed clarity that other equipment did. The hope that end-to-end linear phase measurements of individual pieces of equipment could describe a system’s ability to reproduce a good sound stage was again in doubt. Something else appeared to be influencing this ability.
A "subjective vs. objective" battle ensued where these two camps dismissed the opinions of each other for one reason or another and a severe split ensued between them. The subjective camp asserted that the objective camp is listening to music with their eyes and the objective camp asserted that the subjective camp cannot reliably choose what is heard in double-blind tests. This split ensues today with no resolution in sight.
But the fact remains that both camps are correct in their own realm. Low distortion of individual pieces can translate to higher accuracy but poor 3-dimensionality relates somehow to an overall system distortion. Experimentation revealed that the position of speakers in a room changed the size and shape of a sound stage. And since most homes have rooms that severely limit loudspeaker positioning, a clue to making a large sound stage was uncovered.
Early attempts in properly locating the two independent loudspeakers to optimize this sound stage effect took several approaches, one of which focused on bass. Starting with loudspeakers in the center of a room (equidistant from all walls, floor, and ceiling), people found it produced X amount of bass (what can be termed as the reference bass level or 0dB). Moving the loudspeakers against a wall but still centered on that wall produced +3dB more bass than the reference level. Moving the loudspeaker down against the floor but still centered on the wall produced +6dB more bass, then moving the loudspeaker into the corner and on the floor produced +9dB more bass. So to hear as much bass as possible, both loudspeakers soon occupied the corners of the rooms.
Loudspeaker Position Influenced Loudness
However, by enhancing the bass level the soundstage depth/width/height suffered. When loudspeakers were against a wall, it returned the holographic soundstage effect to a 2-dimensional “wall of sound” losing that highly prized 3-D characteristic. In addition, rooms with complicated wall angles or non-parallel walls proved to be a challenge in finding reasonable loudspeaker locations that revealed a good-sized holographic soundstage while fitting into the compromises of daily living.
Also noticed in this positioning process was that to fully appreciate this holographic effect, this synergistic interaction could best be appreciated from only one location in the listening room, termed the “sweet spot.” The further away one listened from this sweet spot, the perception of the soundstage degraded as was the smoothness of the bass. Even when listening from the optimal sweet-spot position, normal room furnishings such as chairs, tables, and lamps, all impacted the size and shape of this holographic effect. To help correct for these room interactions, sound absorbing and diffusing products flooded the market with names like ATS, Auralex, pArtScience, RPG, Sonex, SonoMatt, Tube Traps, and many others. Combined with loudspeaker positioning, strategically placed products help to enhance the shape of the psycho-acoustic hologram and control dips and peaks in a room’s resonances, reverberations, and acoustic reflections.
A Sound Diffuser
So it quickly became clear that room shape, loudspeaker positions, sonic treatment, and location of the listener all interacted with each other in a synergistic way that not only influenced the size and shape of the soundstage but also the level and smoothness of the system’s perceived response. Some extreme audiophiles even went to the pains of designing listening rooms in newly constructed homes with specific dimensions so as to minimize these annoying issues. Today, custom home theaters use this same exact approach.
Unfortunately, most audiophiles do not have the luxury of designing a listening room from scratch but rather must recruit a room in their existing home that would best serve this purpose. So what type of room is the ideal room for the chance at getting a really good sound stage? Good question and one we will investigate in Part 3 of this series.
Yours for higher fidelity,
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