The Drivers
ADS manufactures all
of the drivers used in its speakers. This fact alone distinguishes ADS from a
large majority of speaker system manufacturers, who must purchase most or all
of their drivers from bulk suppliers. ADS thus maintains total control over system
matching quality and engineering improvements. Proper design and manufacture of
the drivers obviate the need for unnecessarily complex, efficiency-robbing
crossover networks typical of many "sophisticated" speaker systems
which represent nothing more than valiant attemps to match inherently
incompatible drivers. Each ADS driver, furthermore, embodies the most advanced
design, materials and manufacturing techniques in the industry.
The Tweter
The L620 (L520 and
L420) have in common ADS 1-inch acoustic suspension soft-dome tweeter, which
accounts for their ultra-clean, "airy" high-frequency response. This
unit's unusually small diameter and precise shape results in high-frequency extension
and wide, uniform dispersion unmatched by other designs. The dome is
constructed of a super-light fabric-like material coated with a proprietary
"sticky" damping compound. It has none of the "ringing" and
other resonance-related distortions common to other materials. Soft to the
touch, the tweter nonetheless functions as a perfectly stiff piston through its
operating range, thus ensuring low distortion and coloration.
The tweeter's voice
coil features a sophisticated and unusual single-layer winding. (Most similar
tweeters must use two layers of windings in their voice coils to achieve the
required number of turns.) Although difficult to execute, this technique yields
an incredibly high force-to-mass ratio through lowered moving mass and
increased magnetic field intensity. Further aided by a powerful Barium Ferrite
magnet, the ADS 1-inch tweeter delivers superb high-frequency extension,
excellent transient response, extremely low distortion and high efficiency.
The tweeter also
features an all-metal voice coil structure which is unsurpassed in dissipating
heat. Its narrow-gap magnet design, more-over, promotes efficient thermal
transfer for effective cooling of the voice coil during high-current drive.
This "air-cooled" voice coil structure can only be achieved through high-precision
assembly, and it is more efficient than "liquid-cooled",
ferrofluid-filled systems. It should not be surprising, therefore, that very
few tweeters, including those with voice coils of larger diameter, can handle
as much power as the ADS 1-inch soft-dome tweeter.
All ADS soft-dome
tweeters, furthermore, feature airtight cavities behind the diaphragm. In
effect an independent miniature air suspension system, the tweeter enjoys total
acoustic isolation; and, equally important the trapped air acts as a highly
linear diaphragm "spring" which does not deteriorate with age as in
other designs.
The Woofer
While a woofer
obviously need not be as light as a tweeter, low mass (relative to a given
driving force) is an absolute necessity for well-damped, hangover-free bass. A
woofer cone must simultaneously be as "dead" as possible - it must
have a high degree of internal damping -
in order to avoid imparting its own chaaracter to the sound. (Tapping a
woofer cone with the eraser-end of a pencil should produce a dull
"thump" rather than a sharp, "live" sound.) and yet, the
cone must be as stiff as possible in order to avoid "breaak-up" and
other non-piston;like behavior. These three seemingly contradictory
requirements take on added importance in two-way designs because the woofer is
called on to accurately reproduce midrange frequencies in addition to bass
information. While many driver manufacturers have used various exotic materials
in attempts to meet these requirements, ADS firmly believes it has the closets
thing yet to the ideal woofer cone: Stifflite
The L620 (L520 and
L420) have 7-inch (8-inch and 10-inch) diameter woofers, respectively. All
three woofers feature ADS tapered Stifflite cones. Stifflite is a relatively
thick material formed of air-filled, randomly-oriented pulp liber in a unique "sandwich"
construction. The internally trapped air damps resonances and keeps the
structure very light, while the thickness of the construction lends high
structural rigidity. And yet, the Stifflite cone is thick only where it needs
to be - toward the outer edge - and tapers off where the extra mass is not
required for rigidity.
Coupled to each cone
are a low-mass high-temperaature metal voice coil at one end, and a highly
flexible and uniform rubber surround at the other. The voice coils feature two
layers of windings (where most other woofers use four), and they are precision-aligned
into deep, narrow magnetic gaps. The results speak for themselves. The woofers
have exceptionally light moving systems (lighter than voice coils alone in
typical competitive designs). They excel at midrange frequencies, a sore point
with most larger two-way systems. They do not "color" the sound, and
their ability to excurse freely and linearly makes possible surprising aamounts
of deep, undistorted bass. Correctly dimensioned Barium Ferrite magnets coupled
with low moving mass ensure high efficiency and damping. The woofers boast
exceptional power handling capability thanks to their high-temperature voice
coil assemblies. Their efficiency and power-handling combine to give the L620
(L520 and L420) unusually wide dynamic range.
The Crossover
Network
Many speakers have
crossover networks with numerous power-robbing, distortion-inducing components,
which are needed to correct driver performance anomalies and match grossly
different driver efficiencies. Other have ridiculously simple, inexpensive
crossovers too embarrassing to show or discuss in literature. ADS networks are
necessarily sophisticated because musical accuracy is highly dependent on
proper transition from woofer to tweeter. But, thanks to ADS advanced driver
technology, ADS crossover networks are free of excessive complexity and have
the lowest power loss and distortion figures in the industry.
The crossover
characteristics and frequencies for the L620 (L520 and L420) systems have been
selected through computer analysis and extensive acoustic measurements and
extensive auditioning. The network components, furthermore, are of the finest
quality. All critical capacitors, for example, are computer-grade metalized
polyester-film rather than the more common and less expensive electrolytic
variety. Bass section inductors are "over-designed" with
extra-heavy-gauge copper wire and special low saturation, low dynamic
distortion ferrite cores. All high-frequency inductors are air-core designs.
The coils, as a result, are extremely linear over the system's operating range
and have the lowest measured DC resistance among modern production loudspeakers.
The corossover networks of the L620 (L520 and L420) thus provide seamless
transition from low to high with maximum daamping and minimum distortion
throughout the speakers entire frequency and dynamic range.
Advanced Acoustic
Suspension Design
All enclosed ADS
speakers employ the acoustic (air) suspension principle for two basic reasons.
First, it is ADS belief that a properly designed acoustic suspension system
offers the best, most consistent bass performance for a given size and cost,
for the widest range of applications. Second, since acoustic suspension
provides a highly linear diaphragm restoring force (trapped air) which is not
dependent on the mechanical suspension of the driver, it delivers the most
stable performance over years of use.
ADS acoustic
suspension designs, however, go far beyond these basic considerations. ADS
superior drivers and networks ensure the highest system efficiency. The L620
(L520 and L420) are demonstrably more efficient than other acoustic suspension
systems of comparable bass performance. Surprisingly, they are also more
efficient than most bass reflex systems of comparable internal volume and bass
rsponse, even though theeory dictates the revers. (Most bass reflex systems
lose their theoretical efficiency advantage to poor drivers and/or networks)
This enables the L620 (L520 and L420) to be driven to startling sound levels
with amplifiers as small as 15 watts per channel, an important economic
consideration since amplifier power is not a cheap commodity. ADS acoustic
suspension design, furthermore, ensures maximum bas accuracy and extension. All
parameters are carefully chosen to maximize system damping and provide a
smooth, gradual bass rolloff. Unlike "one-note" boom boxes which may
initially impress the unseasoned listener, the
L620 (L520 and L420) produce bass of substance and subtlety,
apprecaiation and enjouymebt of which can only grow over years of ownership.
The Enclosure
The L620 (L520 and L420) cabinetry is a supreme
example of ADS attentionto detail. The enclosures are precision-constructed
from 3/4-inch extra-high-density particle board, which provides the mass,
rigidy and acoustical properties necessary to keep sonic coloration to an
absolute minium. They are beautifully finished in select natural walnut. The
drivers are carefully flush-mounted onto the piano-finish front baffle to
minimize surface diffraction effects.
The curved metal grille is acoustically transparent, and it eliminates the need
for frames and supports, which cause further diffractive interference in
conventional grille designs. ADS thus achieves remarkably diffraction-free
performance in the L620 (L520 and L420)
without resorting to unusual, and frequently unsightly cabinet shapes. The lack
of diffractive interference gives these speakers an open, "unboxed"
sound quality and pinpoint-accurate stereo imaging, characteristics unusual in
bookshelf speaker systems.
Tweeter protection
Since the tweeter is
the most likely driver to be damaged by amplifier misbehavior (including
clipping and oscillating) or abouse, the
L620 (L520 and L420) have tweeter protection fuses located in special
compartments on their rear panels. Spare fuses are included in these
compartments for convenience.
Accuracy Above All
Sonic accuracy is
often defined as a lack of recognizable character. Since ADS believes that
speakers should be transducers rather than sound generators, it should not be
surprising that the L620 (L520 and L420)
sound remarkably similar to one another. They sound, in fact exceedingly like
all other ADS speakers. And you will find this sound exciting and spectacular
only if you find live music exciting and spectacular. If upper-bass boom,
larger-than-life "presence", and sizzling highs are your cup of tea,
you will find the L620 (L520 and L420)
unimpressive and perhaps even disappointing. If these speakers have a sonic
"signature" at all , it is their transparent, effortless and neutral
sound character, a feature common to all ADS speakers.
L 620
Specifications
Frequency
Response: 30 - 20,000 Hz ±3 dB (20 -
22,000 Hz ±5 dB)
Impedance: 6 Ω (nominal), 4 Ω (minimum)
Efficiency: 92 dB SPL with 2,8 V RMS ( 1 watt) pink noise
input measured at 1 m in typical listening room (2000 ft²)
Driver Complement:
HF : 1" soft dome tweeter
LF : 10" Stifflite woofer
Crossover: 1,500 Hz
12 dB/octave
Power Rating: 75 watts (nominal), 150 watts (max peak program)
Recommended
Amplifier Power: 15 watts (minimum), 150
watts (maximum)
Cabinet: Selected natural walnut over
extra-high-density particle board
Baffle: piano black finish with diffraction corrected
flush driver mounting
Grille: Acoustically transparent removable frameless
grill in bronze finish.
Dimensions (Hx W x
D): 25-1/2" x 14-1/8" x
11-3/4"
Weight: 18 kg (40 lbs)
