UHF No 70 (Net).indd - Ultra High Fidelity Magazine

Cinema
WE HAVE MOVED
TO A NEW
LARGER LOCATION!
But, for
Creek
Cyrus
Eichmann
Epos
Visonik
in Winnipeg,
it still has to be
BOYZ ON A WIRE
956 PORTAGE AVENUE
WINNIPEG, MB, R3G 0R1
TEL: 204-256-0462
www.boyzonawire.com
going dead centre. Worse, it strikes the
screen surface at a angle, projecting an
oval onto the screen surface rather than
a circle. That means poor focus at the
edges, worse in the corners. That’s why
most TV screens have rounded surfaces.
Expensive flat screens use electronic
compensation to minimize problems.
Even so, the CRT has a practical size
limit. Its size was once adequate even
for large rooms, because scanning lines
looked crude on a bigger screen. As line
doublers and sophisticated video processors
became common, screens grew.
Not that the CRT has vanished from
home theatre. Most rear projection sets
still use a CRT…three of them in fact,
one for each of the colors used for the
image. Those tubes are turned up very
bright, and projected onto the screen.
They work well, though an RPTV needs
careful alignment to make the three
images converge exactly on the screen.
Even so, they may not stay converged.
Plasma…the imperfect miracle
Huge fl at screens that could be hung
on the wall were a staple of science fi ction
20 ULTRA HIGH FIDELITY Magazine
years before they appeared. You may
recall the wall TV sets in Fahrenheit 451,
based on the Ray Bradbury novel. The
plasma screen appeared to be the realization
of that long-predicted technology.
Indeed, its futurist look drew a lot of
early adopters, at least ones with deep
pockets. Prices have dropped dramatically,
but they are still not cheap. Nor
are they perfect.
The plasma display is inherently
fl at, because there is no scanning, as
there is with CRTs. Each tiny module
of the unit contains an inert gas trapped
between two glass plates. At the rear is
an electromagnetic exciter, which heats
the gas so it emits ultraviolet energy.
A phosphor coating on the front plate
glows in the appropriate color. A plasma
screen throws off a lot of light, and it is
an eye magnet in high end stores.
The drawbacks? There’s more than
just the price. The gas takes a short but
fi nite time to heat enough to glow, and
some screens have diffi culty following
movement, which is why demos are
mostly done with landscapes. Contrast
ratios are poor, making for punchy
images but little nuance. The screen
may be thin, but it is heavy, fragile and
energy-hungry, and hot…
And, oh yes, it has a fi nite life. So
do CRTs, but they don’t cost as much.
Tossing out a burned out plasma screen
can make you cry, and you may replace
it long before it goes dark, because it is
prone to burn-in: the pixels most used
will darken fi rst. Ouch!
Liquid crystals
The fi rst LCDs showed up over a
quarter century ago in pocket calculators.
An LCD is a diode with an intriguing
property: apply a voltage to it, and it
will darken. That’s how LCD elements
can form the digits on your calculator or
your watch.
On a video or computer screen
they are used differently. Tiny LCDs
are placed behind a colored fi lter, and
depending on its voltage state it will be
transparent, letting light through, or
opaque. A large fl uorescent bulb and
diffuser behind the LCD lattice light
up the resulting image.
LCD screens are turning up on a lot
of computers, as already noted, but also
on TV sets. They are costly, but they are
light and they use little energy, which
is perfect for laptop computers. They
require no convergence adjustments
There is no burn-in effect, and changing
a bulb is potentially cheap, though some
displays have bulbs that are astoundingly
expensive. Check before buying.
You should know that LCDs have
their own problems. You can pay $700
for a display not much larger than a
magazine cover. Like plasmas they
can be slow to react. They can suffer
from “stuck” pixels, jammed either on
or off, and that may not be covered by
the warranty unless there are lots of
them. Colors shift as you move off axis.
LCD images can look crude at close or
medium quarters, because the individual
crystals are clearly visible.
And the LCD panel has one other
drawback seldom mentioned: the range
of colors is narrow. The color gamut
chart is misleading, even so, because the
fl uorescent bulb used as backlighting
does not emit a continuous spectrum.
Use a prism to see the fl uorescent spectrum,
and you’ll see a series of discrete
lines rather than a full rainbow. Add to
that the fact that LCDs have trouble
with deep blacks.
Note that some manufacturers,
notably Sony, now make rear projection
TVs using LCDs rather than CRTs.
Our judgement stands.
Digital Light Processing
The DLP is an invention of Texas
Instruments, a one-time electronics
powerhouse that hadn’t done anything
this original in years.
The heart of the DLP is a tiny mirror
controlled electronically so it either
refl ects light toward the lens, or else into
a “light sink,” a black absorbent surface.
Early DLP projectors had blacks that
were closer to grey, but the rest of the
spectrum was superb, with bright,natural
colors, no burn-in, and a long lifespan.
Replacement bulbs are inexpensive and
are user-installable. Perfection?
As with plasma, the cost was something
of an obstacle, running into the
tens of thousands of dollars. The tiny
DLP modules would surely come down
in cost, but in the meantime there was
a trick that could drop the cost by two-