6
I L L U S I O N A 7 F E A T U R E S
1
The geometrically complex form of the A7 enclosure
provides nearly ideal acoustical behavior, with non-
parallel plane surfaces, precisely calculable volume,
and peerless strength, rigidity, and freedom from
unwanted vibration and resonance. The overall cabinet
is a vented system (woofers) via twin rear-facing ports.
2
The smoothly elliptical radius of the I
LLUSION
A7 baffl e
(front surface) reduces re-radiation or “edge-diffraction”
for cleaner and smoother response at midrange and
high frequencies, especially off-axis. Snell pioneered this
technique in the original Type A system 30 years ago.
3
The A7’s true D’Appolito array is one of a very few
such that is genuinely entitled to the name. This
extensively computer-modeled, highly engineered
construct yields a nearly perfectly coherent forward-
radiating wavefront, with a combination of precisely,
moderately controlled vertical directivity and broad,
smooth horizontal dispersion that approaches the ideal
for a two-channel reproducer.
4
The A7 midrange is a proprietary driver developed
specifi cally for the I
LLUSION
design. A unique cast-
magnesium cone, machined to a thickness-contour
designed to optimize stiffness and minimize mass, is
surface-treated for strength. This singular diaphragm is
combined with a natural-rubber surround to elimi-
nate edge resonance, and the proprietary Hexadym™
magnet that anchors an enormously powerful “motor”
with vast dynamic linearity and power handling. (The
unusually open Hexadym structure further provides
free air movement behind the cone, eliminating cavity
resonances and turbulence.) Its special injection-mold-
ed alloy basket is strong, rigid, and provides the un-
restricted airfl ow the A7’s transmission-line midrange
sub-enclosures require.
5
The soft-dome tweeter designed for the A7 develops
smooth, resonance-free response to nearly 40 kHz, as
well as powerful and accurate output to unusually low
frequencies. This facilitates an atypically low midrange/
high crossover point, critical to the A7 D’Appolito array’s
ideal combination of amplitude and directional smooth-
ness. A scaled-down Hexadym magnet (similar to the
midrange’s) is highly effi cient, with an acoustically open
structure that frees the tweeter sub-enclosure to negate
backwave and internal-resonance factors.
6
Each A7 midrange operates in an individual, vibration-
isolated, transmission-line-terminated sub-enclosure.
This effectively absorbs the transducer’s rearward-radi-
ating energy or “backwave,” eliminating its unwanted
cancellations and nonlinearities from infl uencing
midrange motion, or from contributing to port output.
7
The proprietary A7 woofer’s aluminum-magnesium
alloy diaphragm is cast, machined, and surface-treated
similarly to the midrange’s. Matchless stiffness-to-
mass, a two-inch, high-temperature voicecoil, an
oversized T-shaped polepiece with heavy copper “sand-
wich” rings and phase-plug are but three of the many
factors that underpin this driver’s enormous dynamic
range, power handling, and linearity. Specialized 12
Ω
windings match the A7 woofer-pair ideally to the mid-
range/tweeter array, for absolute bass precision and
perfect low-to-mid transitioning. The driver’s extraor-
dinarily stiff, injection-molded alloy basket combines
superb structural stability with huge “windows” for
air movement, making it acoustically invisible at low
frequencies and so reducing refl ections, cavity reso-
nances, and turbulence-noise to insignifi cance.
8
Removable grille brackets accommodate the cloth
covered grille. This frameless design reduces high-fre-
quency diffraction refl ections. The custom-perforated
pattern is calculated for acoustic transparency. The
grilles are iso-mounted to decouple induced vibrations
from the A7.
