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Discussion Starter #1
I have been playing around with designs for a new subwoofer for a few months now and just can’t seem to find a combination of driver(s), cabinet and performance that excites me enough to start building. I now run a sono sub with a 15” Blueprint drive tuned to 20 Hz that I’m pretty happy with. The new sub would have to be an improvement over this sub and be attractively priced to justify the cost of the upgrade.

I see that the Shiva-X is on sale for $149 plus shipping. This has got me thinking about building a set of subwoofers, each with 2 drivers, both mounted on the front of the enclosure, tuned to 15-16 Hz. I like the idea of using 12” drivers because it keeps the width of the tower to a minimum. The basic size of the tower would be 13-1/2” wide, 45” tall and 17-1/2” deep, the front wall would be 1-1/2” with the rest being braced ¾”. I can add to the depth to the design if needed. I would wire the drivers in sets of two (wire the voice coils in series and the drivers in parallel to produce an 8 ohm load) and drive each set off one channel of my Yamaha P7000S. This would give me approximately 350 watts per driver from one amp so I may need to add another amp to get top performance.

Here’s the strange thing, using the same drivers with the same power input, in the same cabinet size, the graphs in Unibox are very, very close. I think this is because you have to subtract the port volume which gives you a smaller internal volume for the ported sub verse the sealed sub, 135L vs 110L. This leads to estimated outputs of (sealed vs ported) 109db-109db at 20hz, 104db-106db at 15hz and 98db-100db at 10hz. This does not take into consideration, the second subwoofer. It looks like the sealed design is the way to go considering it doesn’t have any of the drawbacks of the ported design and drop off in performance shouldn’t affect me. If something doesn’t look right in my calculations or assumptions, please let me know.

How would a design like this compare to a Mal-X with two 18” PRs?
 

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Below 15Hz the Shiva-X:es would have more output in my example. Otherwise it's pretty much the same. I'd go with the 4 Shivas, but you'd end up with two big boxes, enormous (long) ports...

Maybe 4 sealed Shivas and equalization?
 

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Discussion Starter #6
Yes, the Shiva's would be two 135L boxes with 2 drivers each (sealed) vs one Mal-X with PRs.

In the present room, both Shivas would be placed in the same corner, somewhat of a sub array. In the future HT room they would be laid down end to end on the floor in front of the projector screen to create a sound bar style sub.
 

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Discussion Starter #8
I had a question about the Gen II version of the Shiva-x. The present version has duel 8 ohm voice coils, where as the Gen II will have duel 4 ohm voice coils. So, if the drivers keep the same efficacy and my amp doubles it’s output from 8 to 4 ohms, I should get the same output driving 4 Gen II Shiva’s with one amp compared to 4 Gen I Shiva’s with two amps.

Is this possible? What am I missing? If so, the cost savings by not buying a second amp well out weighs the increased cost of the Gen II Shiva’s.
 

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Discussion Starter #11
Well this is the design I am looking at. It's 15" x 17.5" x 46" with an internal volume of 135L.



In this design, I have the drivers equally spaced, is it better to have them closer together?
 

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Discussion Starter #12
This is the way I see the wiring for this set. The Shiva’s have duel 8 ohm voice coils and there will be 2 drivers per cabinet and both cabinets will be driven by a single Yamaha P7000S bridged.

• The voice coils on each driver will be wired in parallel creating a 16 ohm load per speaker. (each speaker’s voice coils will be wired positive to positive, negative to negative)
• The cabinet will have one set of terminals and wire the two drivers in series creating an 8 ohm load at the cabinet terminals. (Cabinet positive to driver1 positive, driver 1 negative to driver2 positive, driver2 negative to cabinet positive)
• The cabinets will be wired in series with the amp creating a final mono load of 4 ohms. (amp positive to cabinet1 positive, cabinet1 negative to cabinet2 positive, cabinet2 negative to amp negative)

Trying to be conservative, with the P7000S outputting 2000 watts @ 4 Ohms, each driver should see about 500 watts. If I wanted to use the subs in stereo, I would need a second amp and bridge both of them and have them each drive a single cabinet with 1900 watts @ 8 ohms each.

I am banking on this system to fill a 3360 cubic ft Home Theater with a flat bass response down to 15hz, not an easy task for a sealed design. A Unibox model of one cabinet shows an output of 105 spl @ 15hz if each driver is fed 600 watts.

OK, what am I missing or where is the mistake in my assumptions?
 
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