Shiva+PR15 Subwoofer (Work in Progress)

3-August-2003

It's been over 2 years since I made the first test box. I wasn't too thrill with its un-equalized response and the size of the box made it rather unappealing. The next step was therefore to shrink the box to about half the original size. Using the original box, I made a new one measuring 16-5/8 x 15-1/8 x 18-7/8 inches on the outside for an internal volume of just over 2 cubic feet (not accounting for the driver's and passive radiator's rear volumes). But that still wasn't quite right.

[new box, upside down, 186,120 bytes] Here is the new smaller prototype box.

The real problem is that I don't really have a use for this sub yet. The original use for this sub fell through and so this project has had no calling. And so the new smaller box is partly to allow the drivers to be stored on a baffles while I decide what to do with it ! I placed the drivers in adjacent faces of the box mainly to allow me to place the unit in a particular place in my house for "temporary storage". The box is still nothing more than 3/4 inch MDF with absolutely no bracing of any sort. No attempt was made to "do the job right" since the probability is high that a new box will be built once a final plan is made. This box does however provide a reasonaly test platform for designing the EQ and crossover circuitry that will eventually be needed.

Like the sub, the amplifier for this unit has also languished. Here is the current state of the LM-12 based amplifier.

19-July-2001

I've owned a original Adire Audio 12 inch Shiva (not the Mark II) since 1999 and up until recently, it sat quietly on the floor in its original box. The only more lonely looking thing was the 15 inch PR15 that sat beneath it. Both cried out to be used but my original plans for a home theater subwoofer were stalled for various reason I won't go into.

As luck would have it, we had a need for a subwoofer in the office lab. This was the perfect excuse to use these drivers.

What follows is work in progress and may take some time for the whole thing to come together. The overall plan calls for a powered subwoofer using a passive radiator. A built-in equalizer will boost and flatten the low-end and allow for level of "tuning" to allow usage in both large and small rooms.

Prototype

The prototype is a simple box used to get up and running. It's the largest box I intend to use and during future tuning, I will decrease the volume of the box by adding blocks inside the cavity.

June 24, 2001

[top of driver, 101,725 bytes] Here is the Shiva 12 inch woofer (left) and PR15 passive radiator (right)

[bottom of driver, 102,695 bytes] Here is the bottom of the 2 drivers. Note the space in the cardboard tube at the center of the PR15.

[weight added to the PR15, 106,596 bytes] I added 726 grams of mass to the passive radiator by adding ninety (90) 3/8 inch zinc hex nuts with 4 ounces of wax. This is pretty easy to do. I melted two 4 oz of wax into a clean tin can by heating the can it in hot water. Layers of nuts were then added to the space in the center of the passive radiator and held in place with melted wax. Each layer was allowed to cool and solidify for a few minutes. Both the nuts and wax container were carefully weighed before use. When done, the wax container was weighed again to determine how much wax was actually used. Added to the original mass of 285 grams, the new PR has a moving mass of 1011 grams which is the upper bound of what I expect to have. The final mass will be determine through further tuning.

June 25, 2001

[prototype box, 92,181 bytes] Here's what the prototype box looks like. It is made from 3/4 inch MDF and has internal dimensions of 30 inches (height) by 15 inches (width) by 13.5 inches (depth). This creates a volume of 3.5 cubic feet or 99 liters (not counting anything else that takes up space in the cavity). The small rectangular hole in the rear of the box is for the terminal cup. Another identical (unseen) hole is located just beneath it for a second cup (one per voice coil).

[prototype box with dowels, 91,058 bytes]. For this box, bracing consists of just 3 dowels that tie opposite side panels together. Screws from the outside hold things in place.

[wheels on the bottom, 130,922 bytes]. These four casters are supposed to make the unit easier to move. The sad truth is that they are cheap wheels and don't turn well. If they continue to bother me, I'll replace them with better ones.

June 26, 2001

[terminal cup and wiring harness, 114,001 bytes]. Here are the other parts that make up the prototype. Once installed, the wires were taped to the bracing dowel to keep them from rattling :)

[prototype with test amp, 70,121 bytes]. The completed prototype with a test amp sitting on top.

[prototype next to NHT1259 sub, 77,930 bytes]. Here it sits next to my NHT1259 sub for size comparison.

Amplifier

The current plan is to build an amp using a pair of National Semiconductor LM12 power op-amps in a bridged configuration.

Equalizer

Details TBD

Real Box

The "Real Box" is the final box built. Its characteristics will be determined through testing of the prototype.

Details TBD

03-August-2003

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