This design originally started out as a single 15" Dayton Series II driver coupled to a 15" PR-15 by Adire Audio.  Needless to say, this was the not final result of this subwoofer.  I was very disappointed with the performance of the Dayton sub in this particular enclosure.  The bass was week, incredibly slow and sounded as muggy as anything I'd ever heard.  Not only that but the driver would bottom out and pop at even moderate listening levels.  I did frequency response plots and although everything checked out fine, the response was very smooth with a gentle roll-off beginning around 25 Hz, the actual real-world performance of this sub was less than acceptable.  Within 45 days I returned the sub to Parts Express and simply exchanged it for the Ultimate Attitude 15" subwoofer which had just come out at the time and was on sale for the same price as the Dayton.  You can read about the box I built for the Attitude in another page.

Choosing a New Driver

So with two 14" cutouts on either end of my huge 4.95 cubic foot enclosure (140 L) that fit two 15" drivers I was left with quite a dilemma - what drivers could I put in this huge beautiful box that I'd just built, without having to completely redo the whole thing?  I looked at various other 15" drivers, seeing as that would be the easiest to directly replace the the old 15", but none of the ones I could find suited my liking.  Once the idea of another 15" driver slowly faded, I started looking at 12" drivers hoping that way I would only have to re-do one of the baffles.  As I began looking at 12" drivers and modeling them for a huge EBS style enclosure with a tuning of 18 Hz, the only driver that I found that would fit the mold was...Shiva.  Could you have guessed?

Making the New Baffle

It was certainly more difficult than I thought it would be to re-build that front baffle from a 14" cutout to only an 11" cutout.  But the final  result looked as good as if the box had never undergone the modification - which was my intention.  I sanded down the entire front baffle (which was already painted in a high gloss lacquer).  It was fun to see that stuff come off and show the bare MDF below.  I fabricated out of MDF two semi-circular pieces which were about 20" total diameter across.  The two halves allowed me to allocate one inside the baffle and mount to to the interior-side of the front baffle with lots of liquid nails and screws.  I then did the same with the other semi-circular baffle, and clamped it all down overnight, which completed the new front baffle.  Now I was left with a baffle that was a total of 1.5" thick and had a 14" round crater 0.75" deep in the middle of it.  I cut out my 11" cutout for Shiva in the middle (offset high) of the old cutout, then made a ring with and ID of 12.25" and an OD of 14" which perfectly flush mounted the Shiva to the new baffle.  It looked great with the Shiva because of Shiva's unusually tall mounting gasket.  I'd recommend all Shiva builders should flush mount this driver if possible.  An extra piece of 3/4" MDF with a 12.25" cutout on your front baffle will accomplish this easily.

New Calculations

With all the extra bracing and boards that went into the enclosure, I re-calculated its new internal volume to sit at 4.75 cubic feet.  Still very acceptable for Shiva - even for an EBS alignment.  Now was time to decide on a tuning frequency for the whole set-up.  Using ported.xls and WINisd, I decided that 18 Hz would be a good fB point to shoot for.  Then using passive.xls I was able to decide about how much mass I was going to need to add to my 285 gram PR to get the tuning just right.  According to the calculations I came up with somewhere around 540 grams total mass required.  Yet since I know the calculations aren't totally perfect, I decided to design a way to easily add or remove mass from the PR's to ease the pain of adjusting the tuning.  Check out my Mass Kit page to see how it was done.  After doing the PR modification, the PR had a mass of about 450 grams.  Well under the 540 grams I calculated I would need, leaving me room to add washers as needed until the exact fB was met.  As it turned out, fB was reached alone without having to add any washers at all.  I was surprised at the vast difference, but I was not totally concerned.  As long as the final fB was actually 18 Hz, that was the only goal.

Giving it a Whirl

Now with the new Shiva driver in place and the PR properly tuned, I gave the system its first break-in run.  The first thing I noticed was the incredible improvement over the Dayton sub.  You could actually hear the bass this time.  The Shiva performed marvelously.  The bass was intensely deep, very rich and full-sounding.  The box rumbled away happily while the PR in the back bounced back and forth heavily as if it was going to yank itself from the cabinet (good thing for t-nuts!)  The most impressive point about this subwoofer was that it truly redefined the word 'subwoofer'.  I mean this sub put the sub back in subwoofer where it belongs.  In-room modes resonated as low as 15 Hz and not only could the bass be felt all around you, it sort of gave you this weird sense of a mysterious invisible presence that would not evade you.  A friend of mine who was majoring in psychology at the time said that it has been proven in studies that continual exposure to subsonic frequencies would drive a man to complete and total insanity.  After witnessing this subwoofer, I can believe it.

Trade-offs to EBS

Now of course in every design there are trade-offs to be made, and this EBS-aligned subwoofer is no different than the rest.  I was somewhat disappointed with its mid-bass level performance.  Such as between about 45 and 65 Hz - the bass region where I feel most of the kick comes from your sub.  It wasn't as hearty as I would have liked.  When compared to another Shiva in a smaller enclosure with a higher tuning frequency, the smaller Shiva sub was overall more efficient and had more kick and punch to it.  The Shiva also seemed to be able to handle much less power before reaching Xmax as compared with its little ported brother.  Granted you could still dump about 300 continuous watts into it, I'd be weary of using any kind of really high powerful amplifier with Shiva in a EBS alignment, especially an EBS Passive Radiator alignment.

Improving the Design

If I could do it all again, I believe I would opt for a very small enclosure, under 2 cubic feet, while still using the PR for a low tuning frequency in the low 20 hz.  Though the deep bass was really cool, I believe that there is a greater percentage of bass content in the higher octaves, say above 30 Hz, with music and movie and therefore I would rather have a subwoofer that hit those notes all the time better than a sub that hits the lowest of the lows only every now and again.  Check out a few designs by John at The Basszone where he models a single Shiva in a 2.5 ft^3 enclosure with 2-15" passive radiators.  I'd venture to say that a sub like that would definitely rock.  I really think the obvious solution is to build two subs, one definitely being an EBS alignment for the truly subsonic material, while the other sub may be an optimally small ported or sealed enclosure for the mid-to-upper bass frequencies.  That way you get the best of both worlds.  And if you're going to be building the subs yourself, you can design both subs to suit all of your exact needs.  We're almost to the point where we've discovered that a single paper woofer with a wizzer cone just wouldn't deliver the full spectrum of human hearing, just like a single subwoofer may not be able to produce the full spectrum of truly unbelievable bass.

The Completed Project

Designing the Enclosure

The Sub, PR and Me

Putting the First Pieces Together

Note the Awesome Bracing Technique

Mounting the Front Baffle

More Bracing

First Coat of Stain

Painting the Front & Back Black

A Little Sanding

The Bottom & Feet

Interior Shot with Insulation

The Backside of the Driver

Almost Done

The PR is About to Go In

Sitting in the Corner with Shiva

Undergoing New Baffle

Completed Baffle for Shiva

Measured Response