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,
Philip Rastocny
I do not use ads in this blog to help support my efforts. If you like what you are reading, please remember to reciprocate, My newest title is called Where, oh Where did the Star of Bethlehem Go? It’s an astronomer’s look at what this celestial object may have been, who the "Wise Men" were, and where they came from. Written in an investigative journalism style, it targets one star that has never been considered before and builds a solid case for its candidacy.
My other titles include:
Copyright © 2015 by Philip Rastocny. All rights reserved.
No comments:
Post a Comment
To comment on this blog, you must first be a member. All comments are moderated.
Note: Only a member of this blog may post a comment.