Speaker Design: Background and Parameters
The Diaphragm
The diaphragm of the Legatia L3 speaker includes its cone and dust cap. The shape, weight
and strength of the Legatia L3 cone and dustcap relate directly to the extended frequency
response of the speaker. The cone and dustcap are both untreated pressed paper. Convex
shaped cones typically have a peak in the upper range of the frequency response (e.g. dome
midranges), so we decided on a concave cone for the smoother frequency response. And
contrary to common belief, most convex cones have a narrow directivity pattern. The concave
cone of the Legatia L3 has a wider directivity pattern, and is excellent for use in “off-axis”
applications.
Our approach to point-sourcing is to allow the midrange driver to effectively play the majority
of the human vocal range; having virtually all imaging cues emanating from one set of drivers
in an installation ensures stable stereo imaging across the fundamental frequencies which
define image placement and definition. The paper cone is critical to tame unwanted cone
modes, resonances, and the classic "cone breakup" associated with most composite cones, but
still be rigid enough for upper midbass response.
The ability of the diaphragm to produce low
frequency information is bound by its resonant frequency (129 Hz), and high frequency
information is bound by the radiation impedance and the diameter of the L3’s cone (65mm).
The Legatia L3 was meant to be used as a dedicated midrange driver in a three-way front
stage system. The three-way designs offer elevated power handling capability, better
midrange transient response, and lower upper frequency distortion over its sibling two-way
system.
The Suspension
Rounding out the face of the driver is an inverted high-loss rubber surround that, in concert
with the spider, provides the compliance needed for the 3" midrange to play upper midbass
frequencies with authority. The spider is attached to the voice coil former and the basket.
The spider acts as a centering device and a restoring force for the voice coil. The surround,
which acts as an air seal between the cone and the basket, adds to the restoring force of the
spider. Another function of the surround is to absorb cone flexure waves as they are
transferred up the cone. You'll also know a Legatia midrange and midbass design by its
inverted surround; this design feature allows for the use of a smaller height grille, and more
flexibility in mounting options.
The Frame/Basket
The basket is a high-quality cast aluminum design, which plays a critical role in aligning the
voice coil and the magnetic circuit. In the case of the Legatia L3, it uses an aluminum basket
instead of a stamped steel frame to ensure idealized clamping strength to the baffle where the
speaker will be mounted and less chance of flex/warping. Finally, a pair of gold-plated
terminals and high-gauge tinsel leads ensure adequate connection.
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