in a downtown theater. The lights are dim and the curtains
the show begin. But when we're at home, it's not quite the
same. And so begins the challenge for those AV specialists
who work in home theater.
and directors have long known that to entertain, they must
capture the imagination of the audience. Composers, musicians,
and conductors also know that to bring satisfaction into the
performance, they must enrapture the audience. To achieve
such abandon involvement, the audience must be cultivated
into a mental state such that they forget themselves and where
they are, being conscious solely of the show, and, thus, becoming
part of the show themselves.
In the movies or live performances, this audience
involvement effect is developed by two means. First, good
material and a good performance is necessary. These factors
lie in the hands of those who produce the show. Secondly,
a good setting must be provided for experiencing the show
and this lies in the hands of those who put on the show. There
are numerous elements that go into and compose a good setting
for a show. A light dimmer might be one. A pull cord for the
curtain is another. Comfortable seats in an even temperature
and draft-free room are needed. Air conditioning noise needs
to be reduced just as the excess light from windows. And the
list goes on.
A/V specialist in home theater is the person in charge of
putting on the show. Part of this responsibility is to get
the equipment operating properly, and the other part is to
create a proper setting so that distracting effects are eliminated.
For the most part, the program material available these days
for home theater is pretty good, and so is the equipment used
to process it. What separates the good from the bad and ugly
in home theater is, in most cases, the distraction factor
of the room. By controlling distractions, the A/V specialist
can bring into play that final touch and end up presenting
a really good show without breaking a leg.
The customer does go to the store to buy both
program material and the equipment. The third element is,
however, a "customer service" commodity. It's the
personal touch part of the sale that only the A/V specialist
can implement. Not unlike high end audio, the home theater
sale goes beyond the equipment-in-a-box mentality to include
the setup. To maximize customer satisfaction and loyalty,
good equipment must be set up in a room that has been organized
for minimal distraction effects. We now turn our attention
in some detail to describing various distraction effects that
exist in home theater.
The home theater audience generally has access
to all five senses: sight, sound, smell, touch, and taste.
Being at the downtown movies can keep all five senses pretty
busy, especially if we like popcorn. We can be easily distracted
from the movie by our senses. Let's say we take a seat --
only to discover that the person next to us is devouring hot
popcorn by the handful. If we don't care about popcorn, only
the noise is distracting. But if we love popcorn, the smell
drives us crazy and we'll probably get up and go buy some
popcorn. The point being that sensory distraction can keep
us from being involved in the movie.
There are two kinds of distraction: primary
and secondary. For the movies, the medium of communication
involves sight and sound. Primary distractions would be things
we see or hear that are not the sight and sound of the movie.
Secondary, but not lightly dismissed, distractions are the
comfort of chairs, temperature settings, and drafts in the
room. Primary distractions from the movie program material
involve auditory and visual distractions. The A/V specialist
will work to minimize A/V distraction from the A/V program
theater is a mix of sight and sound. Two out of our five basic
senses are fed coordinated signals that result in the audio/visual
message experience. Imagine for a moment a video projection
screen displayed inside a room, whose entire surface is covered
with mirrors. The floor, ceiling, and walls would all be mirrors.
Consider the visual confusion you would experience in such
a house of mirrors when the video screen lights up, Which
image would be the real image? The one ahead? Maybe it's to
the left or again to the right? Is it above on the ceiling
or behind you? To some degree, it may not matter which image
is real and which one virtual, as each looks like the other.
On a practical basis, it is the confusion and distraction
that comes from having so many images presented at one time.
Some of the images may be simple, clear visions, of the real
screen, but looking in another direction, we'll see the stacked,
multiple image effect of parallel mirrors that fades away
from us into virtual infinity.
No one would really propose a "house
of mirrors" setting for home theater. Fortunately, the
painted surfaces of most rooms are far from a mirror surface;
they are partially light absorbing, and due to their rough
surface, they are partially light diffusing. Whatever light
reflects off the wall is diffusely scattered in practically
all directions with nearly equal intensity. A blue wall stays
a blue wall no matter where you are located in the room. Blue
is the color reflected, but the reflecting surface of the
wall is so rough that blue light is scattered everywhere.
We are lucky that light is pretty well behaved
in rooms, but we're not so lucky with sound. The room does
become a house of mirrors as far as the speakers are concerned.
For sound, the walls are "acoustically" flat like
a polished mirror. If we could visually See the speaker images,
they would be found all over the walls. Unfortunately, with
sound, the room really does become a house of mirrors.
A good room for home theater will be set up
to control both visual and sonic distraction effects. Before
we can go very far with guiding the home theater room away
from behaving like a house of mirrors, we need to understand
the principle of sensory fusion. Sensory fusion is part of
our natural condition and comes as a mixed blessing. Without
this fusion process, movies as we know them today would be
impossible. Yet, because of it, we become susceptible to sensory
input overload. But first, let's review some aspects of sensory
fusion. There are two kinds of sensory fusion; one involves
time and the other involves space. There is always a limit
as to how close events can occur and still be distinguished
as individual events.
video. It is actually a rapidly flashed sequence of still
images like movie frames. These stills are flipped up to us
at a rate just a little faster than our ability to perceive
separate visual events in time. Hence, this staccato of stills
seems to the viewer to create a continuous motion. The visual
images are flashed at a rate of 60 times/second (every 1 sec/60
or 17 ms) and at that rate we cannot separate one image from
the next. These well-defined still frames are being flashed
to us at a rate faster than our visual reaction time for discrimination
of separate events in time. This is called temporal fusion,
the time period of sensory fusion.
The reason we are slow to perceive the rapidly
flashing visual images is because we employ a slow speed biochemical
sensor (not a speed of light electronic photocell sensor)
in our eye/brain system. The relative slowness of our electro/chemical
visual sensors results in the "visual fusion" of
actually separate-in-time events. It is not a weakness, but
it is the nature of our biochemical being that multiple events
are perceived as separate events, only if they occur sufficiently
separated out in time. If separate events arrive too quickly,
they are perceived as one continuous event. Without this "vision
fusion" process, video as we know it today would be like
watching a strobe light show -- a novelty -- but not an entertainment
Let's utilize this card flipping process to
introduce the sense of sound into temporal fusion. Most of
us have done something like this when we were young. We used
a clothesline clip to position a card into the spokes of the
bike wheel and we got the sound of a motorcycle. Try an experiment.
Take a deck of cards in your hands, arch them back and then
with the thumb, release the entire deck in one second. What
do we hear? A breathy, fluttering type of sound, but a tone
nonetheless. If we flip through 50 cards in one second, we
get 50 separate positive pulses of air per second. But we
hear this process as if it was a breathy 50 Hz tone, which
is a bass note whose location is about four keys up from the
bottom end of the piano keyboard.
If we flip one card per second, we hear distinct
snaps. If we flip 50 cards per second, we do not hear 50 snaps
per second, but perceive a continuous tone of 50 cycles per
second. Because we are human, and our detection systems are
biochemical, our experiences with sight and sound are quite
similar. Rapidly flipped cartoon cards create the impression
of continuous motion and rapidly snapped playing cards create
the impression of continuous sound. Both effects occur because
of the temporal fusion threshold (time) in our ability to
detect separate events. Separate events that occur within
1/20 second are perceived as one event. Multiple events that
are spaced closer than 1/20 second apart are perceived as
a continuous event.
Again, we consider video and find the spatial
(location) version of fusion on the video screen itself. At
the movies, the image is practically a continuous distribution
of colors and shadings because it is a projected photograph
(slide shot) of real objects. The smoothness of the image
is controlled by the graininess of the film, which long ago
was reduced to the levels. Not so with video. We have pixels,
dots, or blocks of colors on the screen. The size of the dot,
its brightness, and distance to neighboring dots is macroscopic.
It becomes visible to the naked eye as we move closer to the
screen. Of course, if we sit back far enough, these separate
dots seem to merge, fuse into a continuous image. Again, sensory
fusion. Separate events in space, as well as those in time,
can fuse together into a continuous event. If it were not
for our susceptibility to sensory fusion in both time and
space (temporal fusion, spatial fusion), we could not enjoy
the film or video process as we do today.
This fine grain fusion threshold has to do
with the distances between adjacent light cones in our retina.
As long as separate distinct light sources on the video screen
are sufficiently close enough together, the cones in our retina
cannot separate the lights. One of the biggest equipment differences
between the movies and video decreased the distance between
pixels, and when viewed from the proper distance, the grainy
resolution problem of TV is improved.
is also a graininess aspect to hearing. This isn't the so-called
"grainy sound" effect that has to do with high frequency
distortion. Here we concern ourselves with listening to a
sound source with one ear and how well we can detect its position
changes. This is like listening to a cricket chirp while it
crawls along the ceiling and you listen with one ear. We detect
this kind of position change by the way sound enters over
the folds in our "ear trumpet." Sound from one direction
engages one pattern of the curves of our ear, while sound
from another direction engages these same curves in a different
pattern. We learn to tell where sound comes from by the way
it is changed by the corrugation of our ears.
A third and very important similarity between
sight and sound is that we have two eyes as well as two ears.
Two sensors, separated but side-to-side, allow us to easily
resolve lateral positions and get a fix on depth positions.
This third aspect of sensing is available to us through the
coordination of our pair of sensors. With sight we can detect
depth, what is in front of or behind. Also with sound, we
can detect if a sound source is close or far from us. The
mechanisms for these detections may be different, but the
effect of stereoscopic vision and stereophonic audition is
clearly due to two sensors and the coordination of their inputs.
We have considered areas of similarity in
the perception of sight and sound. Each contributes, more
or less, to perception in the movie process. We have temporal
fusion thresholds (those due to time) illustrated by cartoon
flash cards and thumbed playing cards. We also have a spatial
threshold on the resolution of distinctly separate source
positions in space. When it comes to the set up of an A/V
room for home theater, the goal is to reduce primary distractions
to the sight and sound process of the movie presentation.
Our perception of a sequence of events depends
on the time between the events. If they are close enough together
(within 1/20 second), the separate events seem to fuse into
one single continuous event. If they are separated out more
than 1/20 second, they appear as a staccato of events, a stroboscopic
presence. A sensory distraction in time usually occurs because
a distracting event shortly follows the main or desired event.
If the distracting event arrives within the sensory fusion
time periods of 1/20 second, we have a fusion distraction.
If it arrives later, we have a "post fusion" distraction.
Let's consider the echo. It is a sensory distraction,
a distinct, post-fusion acoustic event. Sound passes by us,
hits a distant wall and bounces back. The round trip distance,
from the listener to the reflecting wall and back to the listener,
delays the hearing of the reflection more than 1/20 second.
Sound travels 1130 feet/second, and so the distance covered
in 1/20 second is 56.5 feet. A wall half as far, 28 1/4 feet
away or more, will provide a detectable echo.
For light, the temporal threshold is roughly
the same 1/20 second, but the speed of light is very fast,
186,000 miles/second. A reflecting mirror would have to delay
a light reflection by 186,000 miles/second x 1/20 second or
9,300 miles. The mirror would have to be 4,650 miles away
for us to detect the flicker effect of an echo of light.
a room with an average dimension of 15 feet was covered with
mirrors, light could reflect three million times and the images
would still be inside our optical fusion threshold. On a practical
basis, light would die out long before it could reflect three
million times, so the entire optical process of distraction
lies well within the visual fusion time period. We don't have
to worry about optical echo problems. With light we only experience
visual fusion problems, and a little paint or wall paper goes
a long way to control them.
On the other hand, sound travels much slower
and it will cross the room no more than four times before
starting to sound like an echo. In a typical room, sound delay
times are easily 1 1/2 seconds. This means sound can be audible
for over 100 reflections. The first four of these are inside
the sound fusion threshold and the rest arrive outside the
threshold in the post fusion time period. With sound we hear
four fusion distraction reflections and about 100 post fusion
(echo) distraction reflections. Reflections inside the fusion
time period produce an image distraction effect, while reflections
that arrive outside the fusion period produce an echo effect.
The home theater is set up in a residential
sized room. Under no circumstances would anyone ever consider
covering all the walls, ceiling, and floor with mirrors and
then placing a video screen at one end of the room of mirrors.
Such a reflective condition is useful only at the carnival
in the "house of mirrors." What happens in the "house
of mirrors"? Disorientation -- too many images from too
many places. We lose track of the original image source and
certainly cannot dismiss all the reflected images of the source.
The images are too strong and occur well inside the fusion
time period. The source and images merge into one confusing
visual space. And we pay good money for this experience but
only as a novelty -- a game.
We would never really choose to live, work,
or watch a movie in a room filled with distractions. Yet,
all too often with sound, we expose ourselves to just exactly
this acoustical house of mirrors. Normal walls, floor, and
ceiling may not reflect much light; but, for sound, they are
so acoustically smooth they act like a polished mirror. And
this time, it's not the carnival, but your A/V presentation