Wisdom Audio Series S55i - Manual (Page 5)

5
Description
Your Sage S55i subwoofer uses a modern implementation of an old idea for high
quality, low distortion bass reproduction. While the roots of the Regenerative
Transmission Line
™ go back to the 1950’s, it is the combination of modern com-
puter 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 optimiz-
ing its use required both powerful drivers and computer modeling. But if you
are into such things, check out US Patent 2,765,864 (filed in 1955), and an AES
paper published 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 drivers that are specifically optimized for this
application. We call our unique implementation of this relatively old idea a
“Regenerative Transmission 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 S55i
is roughly equivalent to a 8” diameter round woofer, yet the enclosure fits in a
3.5” deep stud bay.
The results are quite striking. Low frequencies are dynamic and responsive, and
integrate quite seamlessly with the fast and detailed Sage Series planar magnetic
hybrids.