Wisdom Audio Series S90i - Manual (Page 5)

5
Description
Your Sage S90i subwoofer uses a modern implementation
of an old idea for high quality, low distortion bass repro-
duction. While the roots of the Regenerative Transmis-
sion Line
™ go back to the 1950’s, it is the combination of
modern computer modeling and the vastly more powerful
motors of contemporary driver design that make the RTL
™
so special.
Regenerative
Transmission Line™
There is a class of bass enclosures that has been around
since the 1950’s, which can be described generically as
“low frequency tapped waveguides” or “tapped pipes.” It
was an idea that was a bit ahead of its time then, since fully
optimizing its use required both powerful drivers and com-
puter modeling. But if you are into such things, check out
US Patent 2,765,864 (filed in 1955), and an AES paper pub-
lished in 1959, “Analysis of a Low Frequency Loudspeaker
System.” We have published both on our website for your
convenience, at
http://www.wisdomaudio.com/support_documents.php
We have utilized sophisticated modeling software in order
to fully optimize our enclosures, and have developed driv-
ers that are specifically optimized for this application. We
call our unique implementation of this relatively old idea a “Regenerative Trans-
mission Line
™ ” subwoofer, or “RTL” sub for short.
All dynamic drivers develop energy on both sides of the diaphragm, with the
rear energy being 180° out of phase with the front energy. If you allow the
driver to operate in free space (no enclosure), the front and rear energies largely
cancel each other out — especially at low frequencies.
In our Regenerative Transmission Line ™ subwoofer, the energy from the back
side of the driver is sent along a long, folded path in such a way that its lowest
frequencies arrive back at the front side of the driver in phase, effectively sum-
ming to an increase of 6 dB in output. Thus, the energy from both sides of the
woofer cone is used in a productive way, resulting in a substantial reduction in
distortion and an effective surface area double compared to what you would
otherwise expect. As an example, the effective radiating surface area in the S90i
is roughly equivalent to a 13” diameter round woofer, yet the enclosure fits in a
5.5” deep stud bay.
The results are quite stunning. Low frequencies are strikingly dynamic and re-
sponsive, and integrate quite seamlessly with the fast and detailed Sage Series
planar magnetic hybrids. As an example, the S90i is easily hidden in the wall,
yet is flat to 20 Hz and can output in excess of 120 dB at 20 Hz (measured at its
output port to minimize the room’s effects on the measurement).