For Something New
Here is a project I have
been wishing I could put together for over a year now. I
have had most of the materials, as well as a general plan for this
project for that long at least. Yet somehow time has not been on
my side and the project has been on the backburner. Yet I think
it may be time to put this thing back into motion once again.
The design starts with a
Shiva MK II Subwoofer by Adire Audio. I have worked with the first
generation model of this driver on a couple of other projects and found
it to be an excellent performing subwoofer. And for the price, it
really can't be beat. One thing that's great about this driver is
its incredible versatility for use in various enclosure designs.
Despite the recent trend for oversized EBS Sono Tubes, that is not the
only enclosure that Shiva will work well in. I'm not a huge Sono
fan myself. Maybe it's because I just can't find it locally yet,
or because so many other people have jumped on the bandwagon, that I
feel I just have to do something different - and you guessed it - maybe
even something a bit innovative. Now don't get me wrong, I've seen
some awesome pictures of some incredibly crafted Sonosubs in the last 6
months. Yet the pictures of a design I'm about to unfold here, has
yet to be seen at all.
The idea stems from two or
three other designs. Let me just point out who exactly were the
influences on the DS-PR1203's design. Namely and foremost - The
Beast by DB. The 10Triple10 by me. The older Klipsch subs
with the single sub and the dual PR's before they were pulled off the
market. And lastly Earthquake with their newly patented SLAPS
passive radiator technology. This sub is designed to be the best of all these
worlds of subwoofers.
Click on the image to see a full
screen and clearer image.
The first solution was and always has been, to make the PR
much like a standard driver (Figure 3). With the use of a
"voice coil" and a solid frame and spider, we can create a
linear back and forth motion that is incapable of cantilevering.
This idea originally became the standard for active driver design due to
its uniform and controlled motion in keeping the voice coil exactly
centered within the tiny magnetic gap.
Despite its overwhelming success in the driver industry,
the design is not without limitations. Since the cone or diaphragm
is suspended between two different forms of spring action (spider and
surround), each one poses its own complex compliance on the motional
behavior of the cone. In most cases, the surround will have a higher
compliance and the spider will have a lower compliance. In other
words, the spider will be stiffer than the surround, and will therefore
provide most of the restoring force for the driver or passive
radiator. According to V. Dickason, "...the spider provides
about 80% and the surround perhaps 20% of the total compliance [of a
Now imagine if we could build a speaker that used no
spider at all. A speaker whose restoring force relied entirely upon
the surround alone. What we would end up with is a speaker with an
incredibly high compliance and therefore very low Fs making it essentially
perfect for passive radiator use. I take another quote from V.
Dickason with regard to passive radiator speaker systems, "If however
the radiating diaphragm is made more compliant than than the woofer, even
low alpha (high Qts) alignments will be more like their vented
counterparts and have acceptable transient response." What this
does is push the Fs (also known as Fp) of the PR farther out of the
passband which causes the roll-off to be less sharp, which is why
transient response is improved.
I have taken on the idea of building a few of these dual
sided passive radiators. I have about 12 of these flat PR's, with which I have drawn up these drawings to scale.
DS-PR12 - Dual Suspended Passive Radiator 12"
CAD Drawing of Enclosure - Top View
Click on Image For Full View
That's all for now. More to come later!