Tannoy TURNBURRY 85 LE, Owner'S Manual

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6
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 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 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.
Low frequency alignment is through the front firing Tannoy Distributed Port System (DPS).
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
precision machined 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 multi-stranded 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 two full 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. Low carbon steel
pole pieces, machined to an ultra fine tolerance, 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,
pressure die-cast chassis locates the whole magnet assembly and positions the moving parts with high accuracy. This provides long-term
reliability and yet does not interfere with the acoustic radiation from the individual sections.
Alcomax 3 magnet
Alcomax 3 is a grade of Alnico magnet, an especially high-energy material. This unusual iron / nickel alloy is doped with cobalt, aluminium
and other rare metals to produce a magnetic material with very special properties. Alcomax 3 has a high remanent magnetism and
energy product. In other words, it magnetises to a high level and retains that exceptional degree of magnetisation. Alcomax 3 is also an
electrical conductor, forming a shorted turn around the voice coils, to effectively null non-linear eddy current effects . These properties
give the Dual Concentric drive unit using an Alcomax 3 magnet an exceptionally clean transient response and increased sensitivity.