SYSTEM DESCRIPTION AND PHILOSOPHY
A loudspeaker design naturally splits into various parts: cabinet, lower frequency, higher
frequency, and crossover which, for the System 600A, is integrated in the amplifier
assembly. The design of these parts cannot take place in isolation, as they are all
interdependent.
The integration of all the features described below is what makes the whole loudspeaker
system even greater than the sum of its individual parts.
Drive unit.
The drive unit used in the System 600A monitors is part of the latest generation of Dual
Concentric units designed by Tannoy. Amongst many other features, this range of
drivers incorporates a dual magnet assembly, ‘tulip’ HF waveguide and injection
moulded polypropylene LF cone.
The design of the HF waveguide has been arrived at by making extensive use of CAD
(computer aided design). It matches the acoustic source impedance at the HF
diaphragm into the acoustic environment, shaping the wavefront as it travels down from
the diaphragm ensuring equal path lengths to achieve a spherical wavefront. Wavefront
shaping begins at the diaphragm surface and, because the compression ratio can be
kept relatively low with this design, the distortions due to air non-linearities are
minimised.
The HF diaphragm is made from aluminium and magnesium alloy, with optimised shape
and thickness, suspended by a precision moulded, inert nitrile rubber surround. Its very
narrow roll eliminates resonances below 25 kHz and provides a very stable and
consistent mounting. The roll form ensures high excursions can take place if necessary
yet provides a fatigue-indestructible assembly.
The HF voice coil assembly incorporates a high temperature copper wire chemically
bonded onto a kapton former fitting onto the outside of the HF diaphragm skirt. The
thermal power handling of the voice coil is greatly increased thanks to its ferrofluid filled
magnetic gap.
The LF unit uses a CNC precision injection moulded polypropylene cone, terminated by
a nitrile rubber, high-compliance surround. The characteristic cone termination
impedance is matched by the surround material independently of the required
suspension compliance. The unit system compliance is provided by the rear suspension
where the best degree of mechanical control can be provided.
The shape of the LF cone has been calculated to match the HF hyperbolic waveguide
ensuring the wavefront remains spherical and perpendicular to the cone surface
throughout the propagation.
The heart of the LF unit is the motor system comprising the magnet and voice coil. The
choice of magnet operating point parameters, air gap flux strength, voice coil details
(number of turns, resistance, winding length, diameter etc.), moving mass, dynamic
compliance and drive unit radiating area presents a very complex mathematical
problem where the solutions can take many different forms. Reaching the correct
answers is much easier if computers can be called on to assist with solving the
equations, as Tannoy do for its drivers.
Cabinet.
As well as the drive units, cabinet design plays a major role in the acoustic performance
of a speaker system. Among the problems which can contribute to the degradation of
the emitted sound field, diffractions and reflections caused by the cabinet boundaries
are too often overlooked although they are the cause of most of the irregularities heard
and measured in the higher frequency areas.
In that respect conventional rectangular, sharp corner boxes perform especially poorly.
On the other hand, the shape of the System 600A has been designed with careful
(3 pages)
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