Prestige CANTERBURY SE Owner's Manual page 7

Running in
Like all loudspeakers, the drive unit in your Canterbury 15 SE requires a while to reach optimum performance, as the stresses in the
materials relax - especially in the suspension system. For this reason, it is beneficial to run the system at fairly high levels at normal
room temperature, for approximately 20 hours to achieve best results.
Tannoy Dual Concentric Drive Unit
™
One of the unique advantages of the Tannoy Dual Concentric™ principle is that the low and high frequency sound radiation is generated
on the same axis. The high frequency unit is mounted behind, and concentrically with, the low frequency unit. High frequency sound
radiates from the centre of the low frequency unit through a carefully designed high frequency exponential horn. Low and high
frequencies are therefore fully integrated at source. It is this feature that gives the Dual Concentric™ driver such unique sound
reproduction qualities.
There are other significant benefits. The high frequency unit does not obstruct the low frequency unit in any way (a unique feature
when compared with other so called coaxial systems). Polar dispersion of sound is symmetrical in both horizontal and vertical planes.
By careful crossover network design the virtual acoustic sources of the high and low frequency units can be made to occupy the same
point on the axis. Therefore the total sound appears to emanate from a single point source located slightly behind the drive unit. This
means that a full and accurate stereo image can be recreated by the loudspeakers when fed from a high quality stereo source.
The Low Frequency Section
The low frequency section of the Dual Concentric™ driver has exceptional power handling and dynamic range. The low frequency
cone piston is produced from selected paper pulp. This is specially treated to absorb internal resonance modes. The completed cone
is fitted with unique rigid reinforcing members to attain a very high stiffness to mass ratio thereby preserving piston action over the
operating frequency range.
The twin roll fabric surround is also damped and shaped correctly to terminate the moving cone and provide optimum compliance and
linearity at large excursions. The cone piston is driven by a high power motor system consisting of a four-layer coil suspended in a
precision magnetic air gap. The coil is wound with a special high temperature adhesive system and individually cured to ensure reliable
operation at high peak power inputs. The shape of the low frequency cone is arranged to provide optimum dispersion of audio frequencies
at both the high and low ends of the spectrum. The cone flare continues the high frequency horn profile to ensure a smooth transition
at the crossover point.
The High Frequency Section
The high frequency driver consists of a wide dynamic range compression unit giving superb transient performance with a smooth
uncoloured response. The compression unit feeds acoustic power through a multiple phase compensating device to the throat of a solid
steel acoustic horn. This horn provides an acoustic impedance transformation to match the compression unit radiation into the listening
environment.
A magnesium alloy diaphragm formed by a specially developed five-stage process produces a piston with a very high stiffness to mass
ratio. Optimum molecular grain structure gives long term durability. A very low mass precision aluminium coil provides the driving
force for the diaphragm, with fine multistranded copper lead out wires to ensure reliability. A rear damped acoustic cavity controls the
compression driver response and ensures further correct acoustic impedance matching to the horn throat.
The response of the compression horn driver extends a full two octaves below the crossover frequency to eliminate colourations that
can arise through operation over the fundamental resonance region.
The Magnetic Circuit
An Alcomax 3 high energy magnet provides flux generation for both high frequency and low frequency driving motors. Precision air
gaps contain the magnetic flux surrounding each coil. The high frequency air gap has a unique shunt member to apportion the total
magnetic flux in the correct ratio between low and high frequency units. This gives an optimum acoustic balance. Precision machined,
low carbon steel pole pieces ensure unsaturated operation, linear flux fields and a high heat sinking capability. High power inputs can
therefore be handled with minimum change of impedance due to temperature effects. A very robust, high quality, precision pressure
die-cast chassis locates the whole magnet assembly and positions the moving parts with high accuracy. This provides long term reliability
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and yet does not interfere with the acoustic radiation from the individual sections.