sub amp thermal protection problem

I have an Audison LRx 1.400 amp with the VCRA volume module.  The amp will shut down due to what I have determined to be thermal overload based on the temperature of the amp.  It is a class A/B amp and I realise they typically run warmer.  The problem will occur quiclky if I cank the volume (1/2 hr) or if it is at a medium-high volume over a longer period of time (1 to 1.5 hrs).  I have 2 Eclipse 8810 DVC subs and have run them at both1 ohm and 2 ohms (2 ohm application using only 1 voice coil on each driver).  All ground connections are to bare metal with dielectric grease. 

I have a very good understanding of audio & automotive systems and have had the amp checked out by the authorised service company under warranty.  No problem was detected.  My local stereo shop that sold me the amp told me that the insallation is adequate.

I first noticed the problem when I introduced a line driver into the system.  I tested it without the LD and came up with the same result.  Same goes for the drivers too.  I borrowed a friends subs and the fault still occured.

My stereo consits of; Pioneer DEX P1 Head unit, Audio Control Matrix 6 channel line driver, Audison LRx 1.400 Mono block, Eclipse 3640 4 channel amp, two Stinger 1 farad capacitors with volt meters, Yellow top, 1/0 AWG power & ground wire to caps (4 AWG to the amps).

The Big 4 have been improved to meet my standards.  I have improved the grounding to the chassis and block, the only thing that I can think of changing, is running a direct ground form the caps to the battery but will that eliminate the problem.

Can anyone shed some light on what may be happening with my system.

Each VC is 4 ohms. If I did all 4, I would end up with two 8 ohm drivers that could only become 4 or 16 ohms combined.  However, if I use 1 VC on each driver, I can achieve a 2 ohm load. 

Physics says that I cannot run a lower impedance to the amp than it can handle.  This is why I increased the impedance from 1 ohm to 2 ohms.  Unless the drivers were grossly mislabled, the subs' impedance would not be less than 1 ohm, therefore not causing an overload.

I have another question.  Will a sub enclosure that is too small, cause my amp to fault as outlined in the above posting. 

I have built a SOLID seald box but I know the volume is wrong.  What style of enclosure will work best in a hatchback and what volume should I design for.  2 Eclipe 8810 4 ohm DVC.

You say the problem began after you installed a line driver?  I assume you properly re-set the gain on the amp after it was installed?  Why did you think you needed a line driver if the system was working before? 

BTW, do not assume that a subwoofer's impedance marking is correct simply because it says so.  These are mass manufactured items and published ratings (for even good amps like the Audisson, too) are typical numbers, not necessarily the exact specs for the item you own.  It is not uncommon to be off by as much as 20% so you could indeed be overloading the amp below 1-ohm.  But what about that line driver first...

Yes, the gains are properly set on the amps.  I don't believe that I am clipping the input signal.  I set the line driver up with the use of a loud CD and adjusted by watching the LED meter bounce around an area less than the peak.

I had picked up an impulse buy digital EQ/line driver for super cheap.  I returned that piece because it was not the right one for my system but I liked the line driver portion.  The LD allowed all of the levels to be their best and brightest.  I mostly wanted it for the mid/hi so they would keep up with the bass.  In my application, the LD is an amazing and now integral piece of the system.  I am hearing little nuances that were never there before.  I will try using a test tone CD to more acuratly set the gain staging.

As for the sub, thats why I tried wiring them to a 2 ohm load.  The chance that the actual impedance could be less than 1 ohm would be significantly reduced.  However, this problem occured even when I removed the LD from the equation.

Bleah, unless your HU output is amazingly low or your amp's input sensitivity very poor, the only time a LD is required is for exceptionally long cable runs.  I suspect you could "hear" exactly what you think the LD is giving you without it as long as the system is set up correctly.  And if you have to boost the signal level to your mains amp in order to "keep up" with the subs, then you really need to either reduce the sub output or replace the mains amp and speakers with higher output units.  But, to each his own, if you like it and your amps are not clipping, keep it. 

I recommend rewiring your subs for a net 4-ohm load (woofer VCs in series and both woofers paralleled to the amp) and reset your gain for the 4-ohm load.  If the amp still overheats, it may be defective.

And, to your other initial question, no, a too-small enclosure will not harm an amplifier unless you overdrive it trying to compensate for the boomy sound and loss of low-frequency output a too-small enclosure will cause.

I believe I may have found the problem with my amp.  I was assuming that each VC was rated at 4 ohms but they are not.  Each VC is rated at 3.1 ohms.  I will rewire to accomodate these numbers.

If you are using a basic ohm meter to check your woofers, you just measured the DC resistance of the voice coil.  Not to be confused with the Impedance of the voice coil, which is an opposition of an AC signal.   

But if this is what it takes to get you to try wiring your voice coils in series, so be it.   Try it and let us know how it goes.

I did not measure the DC resistance as I do not have a multimeter handy.  The 3.1 ohm parameter came from the subwoofer manual. 

I will attempt to rewire the pair.

Thanks for the help.

i am an idiot wrote:

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But if this is what it takes to get you to try wiring your voice coils in series, so be it.   Try it and let us know how it goes.

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Like was suggested originally. 

Thank you both for your help on this matter.   As I did not intend on pushing the amp to the max, I thought I was purchasing an amp that had the headroom that was neccessary for my application. 

So the question becomes, what feature is it that this amp lacks that I need to have in the next piece?  Is a Class D what I need to invest in?  I am not interested in a super loud SPL system.  I would prefer to have an amp that will have higher SQ abilities.

Audison makes some fine equipment, in this case though, the rather small chassis (and therfor small heatsink), prolonged use, summer months and class AB is not what todays subwoofer amplifier should be. As you have just now found out. I would be ideally looking at a class D type amplifier for this application. Where abouts in BC are you?