142L ported Shiva - destroyed twice - advice really needed!

Hi everyone,

About 15 months ago I set out to build my own speakers for use with a 6.1ch amp, I had the first part of my mission completed (building the 6 speakers) within a very short time and for the past year I've been waiting to get the chance to build the sub. Based on the comments around here and on other forums I was convinced that the 12" Adire Audio Shiva would be the best driver to buy. I ordered the Shiva from Acoustic Concepts (Australian Distributor), bought a 350w @ 4ohm amp and built the 142L ported enclosure... with the port facing the amp and I had no bracing in the enclosure. Everythings built, the driver arrives and I mounted it to the enclosure and started playing some sounds. At low volumes the driver made a loud sort of 'pop' with each beat which definately didn't seem right, I'd read that using one voice coil sometimes provided better performance so I plugged in one voice coil. I started 'Die Another Day' and had the volume at 1/3, the first bit of bass starts and then no bass at all, not good. The voice coil had died and I ended up sending it back to Acoustic Concepts, who sent pictures showing the dead voice coil and also said the driver had been driven so hard it was hitting itself (I guess reaching maximum excursion). The driver was sent to his repair person, Ian, and the voice coil was replaced and sent back. Before mounting the driver I took all of Acoustic Concepts advice to move the port away from the amp, so the port is only facing wood, I have also added the full bracing shown in the 'Shiva Vented Applications.pdf'.

So with the design all correct I mounted the driver again and for about a week I've used it to play music and I've been careful with the volume, any sign of strong bass and I'd turn it down. All was going sort of well until about a month ago when I bought 'The Incredibles' and went to test it on my new setup. I set the sub to 1/3 volume, the THX intro starts and after about 5 seconds the drivers dead... again. Taking the driver out and inspecting it showed the glue which was used to secure the basket had failed, so now I'm left with a tear around 1/3 of the basket. In addition to the tear, when pushing down on the driver it makes a scraping noise like the coil is rubbing against something. I sent the driver back to Acoustic Concepts and the report was "The end of the voicecoil former has been crushed into the back of the magnet structure exceeding x-max inwards. Then folded over (internally) by the pole piece as the driver exceeded x-max forward". I still don't know what the final outcome will be, just have to wait some more time.

I've read reports from people using more than 800w with the Shiva, people are saying the Shiva will 'sing' with 350w of power, but from my experiences the Shiva completely dies with 1/3 volume. I'm looking for anyone else who has used this 142L ported enclosure and wondering what experiences you've had with it, I really hope that it is this enclosure which is causing the problems. If I do ever receive this driver back in working condition I'm wanting to build the 88.5L Low-Q design but if I'll get the same, bad, performance that I've had so far then it just won't be worth it. I'm using 6.5" drivers for my mains, yes the Shiva was definately more powerful than them (you'd hope so) but I wouldn't say there was a large amount of bass. Its one of those awful situations where you have the enclosure built and have applied the finish, all to find out that the enclosure would be better as fire wood. Whats even worse is I don't know if I should build another enclosure yet or just wait.

Thankyou for your patience if you read this and any help you can give me.
 
hi

me and a mate recently built the 142l ported enclosure after winning a shiver on ebay- rare driver in the uk! We built it to fill in the bottom end of his fe206e horns for home cinema and music use.
We used the 250w plate amp from cpc, which is the same as the one from parts express. In the enclosure, the driver really shifts some air and we have never bottomed it out even at silly volume that shake everything in the house :D We used a 17inch long 4 inch sewer pipe for the port- its not flared so we made it a bit longer than it says in the plans. Its probably tuned pretty low, so cone flap under port resonant frequency shouldnt be as much of a problem. The enclosure definatly works. The tapping the fishtank bit in finding nemo is rediculous .:bigeyes:
We bottomed the cone out once, but that was messing around with the driver in free air, needless to say we stopped doing that straight away.
Have you checked that the enclosure is airtight, particularly around the mounting bolts? what amp are you using- it might have some sort of eq that is making the driver exceed its xmax at certain frequencies?
 
Two possibilities come to mind, one of them hinted at above already.

First, your port may be all wrong (length) with a resulting tuning frequency much higher than it is supposed to be. Any frequencies below your tuning frequency will cause the driver to 'unload', with massive excursion and breakdown possibly resulting.

Second, your amp could be faulty.

I'd suggest you post a picture and/or provide more description of the box and port size/length so we can give better advice.

Paul
 
The problem could also be caused by a leaky enclosure in which case he'd tend to turn up the volume higher than usual just for more output. Long enough seems that were not completely sealed somehow during construction don't necessarily whistle or chuff at high volumes. As what the others have suggested thus far and I'd say check the enclosure as well for leaks by running a lit candle along the enclosure seems at resonance.
 

Ron E

Member
2002-06-27 10:41 pm
USA, MN
If you are exceeding Xmax to the extent that you are damaging the coil former and spider, you have either made a serious mistake in design execution or you are way overdriving the woofer at low frequencies. I suspect the latter. The shiva can be overdriven with about 25-50W at low frequencies (below tuning) in a vented box.

Thermal powerhandling (the specification) may be around 250 watts per coil, but mechanical powerhandling is a different story. If I were the dealer, from what you describe, you wouldn't get a replacement from me. Smashed/burnt coils and ripped spiders are classic overdriving symptoms.

1/3 of the way on the volume control means nothing at all. I have never owned a piece of equipment where full output was any more than 1/3-1/2 way up on the volume control, unless the source component had very low output.

If you need more SPL, you need more woofers.
 
I used the FP4 from Adire Audio so the vent is flared and 4" by 15", I'm guessing the tuning frequency is the F3 figure which is shown on the ShivaTechSummary.pdf? If it is then its 17hz. I made sure the enclosure is air tight, using lots of glue for all of the parts where the wood made contact as well as beveled edges so everything fit well. The driver was sealed with Moroday Econo-Seal which I was recommended to use for sealing it. The amp has been tested before use with the Shiva on another driver and it worked fine, it was also tested with a multimeter and less than 0.1V DC was present across a wide range of gain levels. Also, there was no audible distortion. I'm still wondering about the difference when using a sealed enclosure, I understand that a sealed enclosure would need more power for the same volume level as a ported enclosure would. Does this mean I'd be able to reach higher volume levels with more power with a sealed enclosure rather than using considerably less than the amp can supply with the ported enclosure?
 
I can't speak from personal experience about bass reflex enclosures.. but I have heard similar stories about the Shiva bottoming easily or being blown from bass reflex enclosures tuned incorrectly.

As another poster mentioned, power handling changes with alignment and tuning. As does sensitivity, among other things.

My personal experiences with the Shiva were in acoustic suspension enclosures of varying volumes. I can say the 88.5L box worked well with my setup and surprised many a folk. Although I was able to bottom it with the 250 PE plate amp, on certain HT selections as well as some test tones. It worked well with music though.