3 x 12" Shiva sub

OzBradW

Member
2005-03-14 1:54 pm
Perth
3 x 12" Shiva sub

My new sub is finally in operation (the project was delayed due to having to move interstate for work). See pictures below

This is where the Construction is currently at.

I have mounted three 12’ Shiva’s in a sealed enclosure and wired with the dual voice coils in series and the drivers in parallel.

The power supply consists of a 50-0-50 800Va transformer, 1 bridge rectifier module and two 100V 10,000uf Epcos capacitors. Measured DC under no load where we are living now is +-72.5V (at home the AC Voltage runs anywhere up to 255 volts with DC measured at around +-77V). This powers a Zappulse 2.3SE amp and at a speaker load of 5.3R as per the Shiva white paper and the power rails above it should be good for around the 500W mark.

The rest of the electronics(ESP Projects) are a regulated +-15V power supply to power the 8 band constant Q graphic EQ and the Linkwitz Transform circuit. the power supply feed from a 15-0-15 transformer.

The enclosure was modelled using WinISD and the Linkwitz Transform circuit was designed to provide an F3 of 25hz. This is the reason for the high powered amp and i selected the Shiva drivers for their high power handling and Xmax.

A couple of commissioning issues along the way, including frying the first amp module! but it is finally up and running.

The Review.

After replacing the amp module I did the initial testing with the rest of the electronics bypassed. I ran the sub using only the amp. The sub physically performed okay, but the sound reproduction was only average. I was not able to incorporate the sub into my sound system that well for music reproduction. Either too little or too much Bass. This said the actual bass itself was a vast improvement over that of my previous ported commercial sub. My wife had never liked the other sub turned on when listening to music in the background during the day (found the woof woof irritating) and even she commented on the improvement.

I then connected the rest of the components up and on the first power up a low volume constant hum was detectable from the speakers (within 1 metre). I currently believe that the Hum is from EM induced noise from the signal leads, so some work still to do with either changing cable types and/or routes. I immediately disconnected and removed the long leads to the phase switch on the linkwitz transform circuit and replaced it with a link and some improvement with the reduction of the noise was noticed.

Initial sound testing showed a small sound reproduction improvement but still not that great.

I then went on and spent around 1 ½ hours using both the sub woofer channel (Gain / Volume) level available on the Marantz AV Receiver and 8 band graphic EQ to level the peaks and troughs in the bass. I have been using a sound level meter and the Digital Video Essentials (DVE) DVD that I have. The DVE disk has an all channel (6.1 channel) frequency sweep from 15hz to 150hz. Whilst I don’t believe that the sound level meter that I have is 100% accurate I managed to get between 25hz and 100hz to be roughly 5db each side of the 0 mark on the meter. When I first started the meter went from hard over one end of the scale to the other thru the sweep. I still have a trough over100hz and then a peak over 120hz where either the other system speakers contribute more volume or the room gain is large. Unfortunately the graphic EQ does not cover frequencies this high. I plan to fiddle with the graphic a bit more and then may consider installing some sort of filter (fixed or variable) in the sub to help eliminate this.

The effort paid off though as the sub is performing great and sound reproduction has been vastly improved over my previous setup on both music and movies with surprisingly no changes to the settings required when changing from listening to music to watching a movie (for my taste anyway).

I certainly believe that incorporating the graphic EQ has paid off. My test DVD for bass is currently Star Wars II (the opening scene where the ship explodes on the landing pad). The bass (and physical speaker movement) was impressive from the sub pre incorporation of the linkwitz circuit. Post this it is just plain awesome. Not much more that I can say than that and I have yet to build up the courage to play the scene at the Marantz’s reference level (at least the house we are in is a rental). The driver excursion is something else!! From the couch 4.5 metres away, if you are wearing loose fitting jeans, you can feel them shaking.

Conclusion

Whilst the Sub needs more tweaking to get rid of the low level hum and possibly the peak over 125hz, it has certainly met my expectations. Yet this sub is not what you could term ‘budget’. Final material costs excluding having to replace the amp module is around the AUD$2,400 mark. Though when compared to a commercial sub that may be able to perform the same, I feel it was worth the cost. On top of that I would feel reasonably confident in saying that it is a one off in its enclosure design. If the design of the enclosure hinders it’s performance in any way, at least I will never know.

I have seen other posts on this site talking about tower subs. I choose a tower due to floor space constraints at my own house. If the room would allow it, i would have probably built two 15" sealed subs. I have seen posts on possible standing waves in tall subs, not sure if this is possible, but i have eliminated the chance of this with the three sloping sides to the enclosure.

Heres some construction photos of the sub

Click on the thumbnails to see larger photos

Heres the amp

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As you can see these photos where taken befor the wiring was completed, and yes that is amp module No. One. This module now resides in my box of bits and pieces. i intend to try to source a new resistor and on of the capacitors that blew to see if replacing them will resurrect the module.

Heres the enclosure

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As you can see with the enclosure, it has three sloping sides. fortunately i have a friend who is good with maths who developed a spreadsheet to calculate the dimensions of the enclosure for the internal volume required as modelled using WinISD.

Most of the timber used was 25mm MDF.

I also sourced some materials from an upholster supplier which i lined the internal with and also installed some wadding.

Heres some photo's of the unit as it is. once the hum is sorted out i will finish it with some veneer and laquer.

[IMGHTTPDEAD]http://www.imagehosting.us/himages/ihnp-553992thumb.jpg[/IMGHTTPDEAD]

Heres the unit with the old 12" sub in front.

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Ok yeah, and it is bloody heavy!!!

Cheers