User guide
5
Description
Your Wisdom Audio STS subwoofer uses a
modern implementation of an old idea for
high quality, low distortion bass reproduc-
tion. While the roots of the Regenerative
Transmission 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 computer mod-
eling. But if you are into such things, check
out US Patent 2,765,864 (led 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 specically optimized for this
application. We call our unique implementation of this relatively old idea a “Re-
generative 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 of the two
15” woofers in the STS is equivalent to four 15” woofers in more conventional
enclosures.
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 STS is only -3 dB at 15 Hz and can
output in excess of 130 dB at 20 Hz.