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C INEXPO WHITEPAPER
Three-way Loudspeakers
for the Digital Age
The Laws of Physics / The Art of Listening
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dB SPL
Frequency (Hz)
Traditional 2-way loudspeaker design
vocal range
woofer compression driver
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dB SPL
Frequency (Hz)
EAW 3-way loudspeaker design
vocal range
woofer
compression drivermidrange cone
INTRODUCTION
The primary requirement of left/center/right main channel
cinema loudspeakers is that they faithfully reproduce the
entire audio spectrum from 20 Hz to 20 kHz. While crisp,
natural reproduction of the vocal range (300 Hz - 2 kHz) has
always been critical to good cinema sound, very high and
very low frequencies (abov e 4 kHz and below 200 Hz)
demand particular attention in the age of digital cinema
audio. The advent of digital technology has brought sound
effects to the very extremes of hearing, filling these ranges
with sonic material which today defines the digital age
cinema experience.
Traditional two-wa y cinema loudspeaker design (a large
cone woofer and a horn-loaded high frequency compression
driver) suffers from an unfortunate 500 Hz crossov er placement that robs dialog of much of its warmth. By requiring
the high frequency compression driver to cover frequencies
as low as 500 Hz, two-w ay design introduces substantial,
audible distortion in the vocal region, leaving voices sounding harsh and hollow .
Similarly , a 500 Hz crossov er compromises a loudspeaker’s reproduction of extreme high and low frequencies.
Transducers (cone or compression drivers) hav e optimal
ranges in which they are most “comfortable” and reproduce
sound most easily . When a driver is asked to go beyond its
“comfort zone ,” distortion and/or inadequate response
result. While it is possible for a two-way design to emplo y
drivers that cover extreme highs and lo ws adequately , it
would require sacrificing response in other frequency ranges
– notably the vocal range.
Finally , for a traditional two-wa y cinema loudspeaker to
achieve adequate pattern control from 500 Hz to 20 kHz,
the horn’s throat must be of such a size that cancellations
within the throat add yet more distortion, typically in the
700 Hz range .
This paper will endeavor to show that b y dedicating a
subsystem to the vocal region, three-w ay loudspeakers are
better able to handle the new demands of digitally edited,
mixed and encoded soundtracks. Compared to two-wa y
designs, three-way loudspeakers impro ve vocal clarity and
warmth, reduce distortion from both horn-throat cancellation and driver excursion, increase the loudspeaker’s pow er
handling capability , and improves performance across the
audio spectrum including extreme highs and lows.
DIVIDING THE AUDIO SPECTRUM
The audible spectrum spans just under 1 0 octav es ranging
from 20 Hz to 20 kHz (20,000 Hz). Frequency is measured
according to a logarithmic scale; for each octave ascended,
frequency doubles. If middle “C” is 300 Hz, then the “C”
above it would be 600 Hz and the “C” belo w , 150 Hz.
Since a single transducer can only effectively cover so
much of this range, two-w ay and three-wa y loudspeaker systems divide the range into high/low- and high/mid/low- frequency sections, respectively .
Our research and experience have shown that a single
transducer’s comfort zone usually spans no more than three
and a half octaves. Yet traditional 500 Hz crossover design
requires the high frequency compression driver to cover w ell
in excess of five octaves .
While compression drivers reproduce frequencies above
1 kHz quite well, much higher distortion result below that
point due to excessive driver excursion. Critical vocal material in the compression driver’s low est octave (5 00 - 1 000 Hz)
falls outside the driver’s comfort zone . The resulting distortion gives voices a harsh, unnatural edge sometimes rendering them unintelligible. One cannot ov eremphasize the
importance this holds for cinema sound; without intelligible dialog, the cinematic experience is meaningless.
By dedicating a subsystem to the mid frequency range ,
three-way loudspeakers effectively eliminate these problems. EA W’s three-w ay designs use large cone woofers , cone
driven midrange subsystems and horn-loaded high frequency compression drivers. W e place crossov er points at specific
frequencies selected to optimize the performance of each
particular loudspeaker system. In general, the low/mid
crossover is set around 350 Hz and the mid/high crosso ver
around 2 kHz.
Simply adding another horn-loaded compression driver
to cover the mid frequency range does not eliminate distortion from the vocal range; in fact, it aggravates the problem.
If excessive driver excursion at 500 Hz causes a compression
driver to introduce significant distortion, distortion at 300
Hz will be even greater . T o eliminate distortion from the
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dB SPL
Frequency (Hz)
2-way w/ compression driven high frequency
distortion comfort
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Frequency (Hz)
3-way w/ compression driven midrange
distortion comfort
dB SPL
vocal region and give dialog exceptional warmth and clarity,
EAW always employs cone drivers for its mid frequency
subsystems.
Since three-way design divides the audio spectrum
between three subsystems , each only needs to cover a little
over three octav es – a range over which each driver can be
truly optimized. The high frequency compression driver
now operates only in the true high frequency range, meaning better performance in the very high frequency range.
Similarly , optimized woofers can better handle the low frequency sound effects that give films that “digital sound.”
THREE-WAY IMPROVES OUTPUT
The maximum volume (peak output) that a loudspeaker system can generate is related to two factors: sensitivity (output
generated by 1 W att of power as measured at 1 meter) and
power handling (the amount of pow er a loudspeaker can
bear before failure).
Horn-loaded compression drivers enjoy excellent sensitivity characteristics but handle relatively low amounts of
amplifier power , particularly when driven at v ery low frequencies (i.e. 500 Hz). By comparison, a horn-loaded,
heavy-duty cone driver is somewhat less sensitive but handles substantially more power . The calculated peak output of
the cone driven subsystem will be 6 - 10 dB higher than that
of an equivalent compression driven subsy stem. Higher
peak output gives loudspeakers a greater dynamic range
throughout the audio spectrum, which particularly
improves reproduction of full range musical scores and
sound effects. It also permits a greater degree of passive filtering to smooth the total system’s frequency response without sacrificing peak output.
ACCURATE WIDEBAND DIRECTIVITY
The ability to put sound where it is needed and keep sound
away from where it is not wanted distinguishes welldesigned loudspeakers. When a loudspeaker with poor
directivity characteristics sends some frequencies at wide
angles and others at narrow angles, listeners at the edges of
its coverage area will hear some frequencies and not others.
Furthermore, uncontrolled soundwa ves reflecting off walls
and ceilings can create unacceptable reverberations that
degrade the sound quality in the entire venue.
The directivity characteristics of a loudspeaker can vary
widely depending on the frequency and the size of the
sound producing device. The rule of thumb goes as follow s:
as the length of a sound wave decreases (with rising frequency) to approach the size of the driver cone or horn mouth,
directivity narrows; as the sound wa ve becomes smaller than
the size of the driver or horn mouth, directivity becomes too
narrow for most applications including cinema. The lower
the frequency , the more difficult it is to confine to a narrow
angle; the higher the frequency , the more difficult it is to disperse at a wide angle.
Traditional two-wa y cinema loudspeaker design uses an
exceptionally large high frequency horn to provide pattern
control at 500 Hz (which it does admirably). But making
very high frequency sound wav es “fill the bell” of the horn
requires an exceptionally long horn throat. So long, in fact,
that cancellation effects within the horn throat cause significant, audible distortion in the 700 Hz region. Smaller format high frequency horns one encounters for smaller cinemas produce much less distortion, but lack the necessary
pattern control at 500 Hz.
By asking each subsystem to cov er a smaller range than
two-way designs , three-way loudspeakers can control both
mid and high frequencies without introducing distortion.
EA W’s larger three-wa y cinema designs – CB223 and
MC4972 – employ smaller format high frequency horns
with very short throats. Since they don’t need to control
sounds in the 500 Hz range, their size is quite manageable .
These horns disperse the highest frequencies across a wide
area without noticeable distortion. Our smallest three-way
cinema system, CB150, loads a compression driv er on our
shallow , throatless W av e Guide Plate™ giving high frequencies an exceptionally smooth character.
EA W’s proprietary manufacturing techniques allow s us to
produce the most mathematically accurate mid frequency
horns in the industry . Automated saw s and routers cut
grooves in the enclosure that accept a flexible hardwood
veneer shell which acts as a form for structural foam which
we inject into the enclosure. The foam/v eneer horn provides
much greater rigidity than fiberglass horns, allowing it to
control mid frequency sound waves with greater ease .
continued
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CONCLUSION
The digital age of cinema audio demands more from loudspeakers than ever before and the systems designed for cinema use must keep pace. Sound effects at the extremes of the
audible spectrum have come to define the digital age cinema
experience and require updated loudspeakers to accurately
reproduce them.
Three-way loudspeakers allow driv ers to operate in more
narrow , optimized ranges, eliminating the distortion that
results from excessive driver excursion. These optimized drivers can then cover their intended frequency ranges more
effectively , without sacrificing response at extreme frequencies. Since three-way design does not ask a single horn to
control directivity from 500 Hz to 20 kHz, pattern control
can be optimized without introducing distortion. EA W
three-way loudspeakers employ only cone driv ers for their
mid frequency sections, providing better pow er handling
and, when necessary , greater peak output than two-wa y or
three-way sy stems using horn-loaded compression drivers
for the midrange. EA W’ s cone driver , selected for their optimal mid frequency response, reproduce dialog with exceptional clarity and warmth.
By moving to accept three-way loudspeaker design as the
new standard for digital age cinema sound, forward-thinking exhibitors can offer audiences the full advantages of digitally recorded, mixed and edited soundtracks which, until
now , hav e only been enjoyed in production studios’ priv ate
screening rooms.
The Laws of Physics / The Art of Listening
One Main Street, Whitinsville , MA 01588 tel··800 992 5013··508 234 6158 fax··508 234 8251 web··http://www.eaw.com
EAW INTERNA TIONAL L TD., Th e Old Coach House, Am ersham Hill, High Wycombe , Buckingham shire , England HP13 6NQ tel··+44 1494 539090 fax··+44 1494 539091
1447 / June 1997
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