THIEL • 1026 Nandino boulevard • Lexington, Kentucky 40511 • USA
Telephone: 606-254-9427 • Fax: 606-254-0075
E-mail: [email protected] • Web: www.thielaudio.com
PowerPoint tweeter
The PowerPoint’s tweeter is a unique and sophisticated
device that incorporates many unusual features that provide
extremely uniform response, enhance output ability and reduce
distortion. It was developed and is built by THIEL and is the
same unit used in the flagship model CS7.2. The most
significant features are:
• Very high output ability and very low distortion is
provided by a very long, 5 mm magnetic gap which allows
linear excursions of 3 mm peak to peak.
• To power the long magnetic gap to field strengths
necessary for high efficiency, an unusual arrangement of a large,
ring-shaped, radially magnetized neodymium magnet is used in
conjunction with an additional disc-shaped neodymium magnet
above the gap. The combined magnet weight of 51 grams is
more than 4 times the magnet size usual in neodymium-powered
tweeters.
• Very long, linear mechanical excursion is provided by a
unusual wide roll suspension that is molded of rubber rather
than thermoformed of plastic so that it possesses low memory,
reducing a subtle form of distortion termed hysteresis.
• In order to eliminate another subtle form of distortion
caused by electrical currents in the voice coil former, Kapton is
used for the former material. Since this material does not
provide the mechanical stiffening of the diaphragm usually
provided by an aluminum former, a diaphragm with a long
shoulder is used that possesses its own stiffness.
• A copper sleeve is used around the pole to stabilize the
strength of the magnetic field which reduces distortion,
particularly at higher output levels, and reduces the coil
inductance and therefore distortion caused by the nonlinear
magnetic characteristics of the steel pole. Reducing coil
inductance also extends the high frequency response.
PowerPoint woofer
In addition to the already discussed feature of a shallow,
reinforced aluminum diaphragm, the PowerPoint’s woofer also
incorporates several other high performance features. Among
these are a very low distortion short coil/long gap motor system
and a copper sleeve around the magnetic pole to reduce the
distortion component of the voice coil inductance. (Please see our
generic technical information paper for details of these
techniques.)
Another unusual feature of this woofer is the utilization of a
neodymium magnet instead of the usual ferrite. Since a
fundamental concept of this product requires the woofer to be as
closely adjacent to the wall surface as possible in order to
eliminate wall interactions, it was necessary to make the woofer
much shallower than conventional drivers. By utilizing
neodymium which is ten times as powerful per size compared to
ferrite, the woofer could be made much shallower than normal.
Measuring the PowerPoint
Since the PowerPoint is intended to be used mounted to a wall
or ceiling surface, representative response will not be measured
when the unit is in the free field or on a stand. It is suggested that
measurements be taken with the unit placed on the floor.
The design axis is 45
°
from the wall surface, on-axis with the
drivers. Since the unit is completely coaxial, representative results
can be obtained with mic distances of only 1 meter.
Axially-symmetric (coaxial) designs can exhibit anomalies
when measured directly on-axis. These are not representative of
the response heard by listeners or measured with mic positions
even slightly off axis. It is suggested that on-axis response be
obtained by averaging several 5
°
off-axis measurements.
Cast aluminum chassis Aluminum diaphragm
Polystyrene diaphragm
reinforcement
Powerful
neodymium
magnet
Long magnetic gap
Short voice coil
Copper
pole sleeve
Typical neodymium
tweeter magnet 12 g
PowerPoint
tweeter magnets 51 g
Wide roll rubber
suspension
Tall shouldered
aluminum diaphragm
Kapton
coil former
Copper
pole sleeve
Short
aluminum coil
Very long
magnetic gap
Neodymium
focusing magnet
Large radial ring
neodymium magnet
