the work bench: The Serpula – a
tapered transmission line loudspeaker
a sketch of the enclosure of this new design.
name Serpula derives from a genus of calcareous marine
tubeworms. It was chosen to indicate the fact that this
entire range of loudspeakers has been optimised for
mounting against a boundary or wall. The first example
was an event loudspeaker, aimed at professional sound
reinforcement. It has been followed by a range of
similarly styled designs for high-end home audio use.
Construction materials for the top, face and back
comprise a laminate of solid 25mm Padauk with MDF, and
the sides are made of similarly reinforced OSB. The
downward-tapering geometry is purely functional and a
set of two carefully selected drivers, one a fullrange
unit and one a supplementary low-frequency driver, will
complete the picture. Features include full-range
operation from 100Hz to 20kHz, with bass extending to
under 40Hz at ±
3dB, sensitivities ranging from 91dB/2.83V to 97dB/2.83V
at 1m, 40W to 350W noise power handling, an easily
driven load impedance, and a minimal first-order filter
= from R15,000.00 (calculated according to size, driver
choices and build details)
off the design bench:
The Serpula SESSS -
a wall-mounted transmission-line/reflex enclosure
Audiophile Loudspeaker System.
the prototype of the new Serpula Single-Speaker-Stereo
loudspeaker, installed in a client’s lounge.
second offering from our new per[form] stable,
the new Serpula design is a hybrid of a short-taper
tuned pipe and a standard reflex enclosure. The
German-designed high-end fullrange driver uses the tuned
pipe character of the enclosure to firm up its lower
frequency response and excursion characteristics, while
the American- or Italian-designed audiophile low
frequency driver, which only operates at full efficiency
between around 40Hz to 150Hz, uses the reflex
characteristics of the enclosure to firm up its
low-frequency response. A high-quality, low-slope,
first-order serial crossover filter assures immaculate
integration of the two drivers.
loudspeaker is made to be mounted relatively high up
against a wall – this is as much a concession to space
considerations as to inevitable boundary
modern, smaller home spaces. Simulations have indicated
that this configuration not only has a positive effect
on the sound character of the fullrange driver, but is
substantially advantaged by the low frequency boost that
accompanies the placement of a loudspeaker against a
boundary. The upward-firing low-frequency driver (in
case of the stereo set) augments this boost effect by
acoustically coupling with the ceiling.
design employs solid hardwood for the face, back and top
of the loudspeaker, and an OSB/MDF sandwich for the
sides. 25mm of solid Padauk wood, reinforced with a 9mm
layer of MDF, was employed in the example above.
loudspeaker has been tested with a range of drivers in
various cost brackets and performs exceptionally with
all of the drivers we have selected. This not only
allows customisation, but makes possible an entry-level
model of this hugely enjoyable and musical loudspeaker.
= R17,000.00 *
The stereo pair will retail at around R30,000.00