Shooting 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.

The first picture below (Figure 1) you can see what is essentially known as a flat passive radiator or a basketless PR.  The PR consists of only the radiating diaphragm and lacks the frame (basket), cardboard center former, and spider.  In theory, this is all that is needed it order for the PR to perform its job normally. In Figure 2 you can see what is a common occurrence of flat PR's - they cantilever.  Since there is no spider or adjoining former to keep the diaphragm moving in a linear and controlled "back and forth only" motion, the PR will have a strong tendency to resist on one side, while giving on the other.  This causes the PR to sustain a good resonance in "wobble land".  This is an unacceptable behavior for a PR and cannot be used in most applications.  As a result of research and design, there are now two ways to combat this problem. Figure 1 Figure 2 Figure 3 Figure 4

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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 driver]".  

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

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