Bigger Amp???

[j-roadtatts 1,129]

So my midbass amp shuts off after 15-20 minutes of hard playing. I am pretty sure I am asking the amp to do more than it is capable of, BUT also know my mounting location is NOT ideal. SO heres the details.

The amp is a Alpine MRP-F600, capable of 300 watts RMS x 2 @ 4 ohms.

I have the amp mounted on the back of the box, with the vents running side to side, in a SEALED trunk.

The midbass drivers are Aura NS10-513-4A, Aurasound NS10-513-4A 10" Subwoofer NLA from Madisound

The Auras are rated @ 200 watt RMS and 800 peak.

I have the Aura's crossed @ HPF 50hz 12db slope, LPF 400hz 12db slope.

The Aura' are mounted IB in the front doors.

There is TWO other amplifiers in the car that never shut off.

Pictures are worth a thousand words So heres the driver mount.

And heres the amp. (left one)

I know the obvious is that the amp is mounted in the worst possible way for cooling.

The next obvious is that the drivers only call for 200 watts RMS.

THE BIGGEST PROBLEM, I think? The Aura's are rated 4 ohm drivers BUT HAVE a WICKED Impedance raise down low. They have an 8 ohm load @50hz, which is where I have them crossed.

I think the Aura's are under rated Because I ASSUME that they are rated at the 200 watts RMS with a full range signal to them. I think the Aura's will handle 400 watts RMS the way I have them installed/crossed. Edit: I think I need an amp capable of 400 watts min. @4 ohms, because alot of the drivers imp. load is closer to 8ohms.

I have had this amp mounted like this for almost 2 years, But not running these drivers. The amp had NEVER shut off with the previous drivers load.

I know I am feeding the amps enough power with a 250 amp DC alt and dual XS batterys, so thats not the problem.

Now for the things I CAN'T/WON'T compromise.

amp/driver locations

crossover points

SO my question is DO YOU GUYS THINK I NEED A BIGGER AMP????? I think I am slowly going to kill this one if I don't do something????? Is there SOMETHING OBVIOUS that I am NOT seeing?????

[j-roadtatts 1,129]

OH how depressing it is. Now the amp will shut off as soon as I turn the volume up past 24, even if I just turned it on. SO DEPRESSING.

Since no one else has any guess's or ideas I will give mine.

I am pretty sure my problem is the impedance rise of the drivers.

Richard (SQ MGB) mentioned in my build log to have an Impedance compensation circuit/network built to solve the problem. I have looked up and attemped to study the Impedance compensator, but am NOT familliar with its attributes in my sitution? I don't know if there is any adverse effects to adding these to my signal??????

SO My questions for today:

Is an Impedance compensator the awnser to my problem?

What adverse affects does an impedance compensator have on the signal?

Is a bigger amplifier still the smartest/best solution?

Thanks in advance for the input.

[Dictator1992 6]

No clue way to complicated for my car audio knowledge (

Did you try testing the amp on some other speakers???Or car?

[sefugi 166]

What about a tester amp to put in it's place just to try then if it corrects the problem find the replacement?

[j-roadtatts 1,129]

I have been using this amp for 2 years, But only started to use it on these drivers a month or so ago. The VERY first day I hooked this amp up to the Aura's and started doing xover sweeps I could put the amp in to protect pretty much instantly. I have tryed narrowing down what frequencys the drivers are playing as far as slopes and xover points go, BUT don't want to lose anymore. I know the drivers are cabable of more power, I just don't have it to give them.

I am looking at a few amplifiers that produce 500 watts @ 4ohm's x2 stereo, So I ASSUME that one of these amps would be capable of producing 250 watts at 8ohms?

I am bandpassing the Aura's @ 50hz and 400hz, both points with a 12db slope. If you are familliar with the Aura's or looked at the impedance graph in the link above, You will see the impedance raises to 8 ohms at 50hz and 400hz, with a 4ohm low inbetween.

So what do you guys think is the best solution to my problem?

[altoncustomtech 773]

I'm of the opinion that the amp has a problem. If it just went from playing for awhile to cutting out immediately when you turn it up there has to be a real problem. I'd start looking for a bad spot in the speaker wires just to make absolutely sure there's no short anywhere for starters. (I know you did a fantastic job running everything in this build, but it's still worth a look) Otherwise, yeah the load could be a problem at high power levels but it still seems to me that the amp should be fine on impedance rise. If the impedance was falling out real low then I could see that being a problem, but rising shouldn't cause the amp to freak out IMO. That's why I think the amp may have an internal problem. On the other hand, an impedance matching circuit (I believe it's also known as a Zobel network) would be ideal to flatten the impedance curve, however I'm pretty sure it would require a little retuning AND the worst problem is that in order to build an IMC or Zobel to handle that kind of power requires some very large (high power handling) coil's and resistor's to handle several hundred watts and that could be expensive to build or even very hard to find the parts to handle 300+ watts.

I dunno for sure, that's just how I see it.

[Impious 1,476]

I really don't see why impedance rise would be a problem or causing the amplifier to cut out. The impedance of a driver could be 20-40ohm at resonance and amplifiers handle this with no problem. I would double check to make sure you don't have any shorts in the speaker wire or the terminals touching any metal. I'm wondering if maybe there isn't a physical problem with the drivers themselves, leads or VC shorting out or something along those lines.

[j-roadtatts 1,129]

I really don't see why impedance rise would be a problem or causing the amplifier to cut out. The impedance of a driver could be 20-40ohm at resonance and amplifiers handle this with no problem. I would double check to make sure you don't have any shorts in the speaker wire or the terminals touching any metal. I'm wondering if maybe there isn't a physical problem with the drivers themselves, leads or VC shorting out or something.

I will check resistance on the speaker wire runs and pull out the drivers and do ohms readings on them too.

I will admit I have overheated the amp a couple of times lately due to long road trips with bags packed in the trunk, up against the amps. I try not to listen very loud with the trunk full, but the amp is going to overheat after being on with no air flow after 8-10 hours anyways.

I will ALSO amit that I could of damaged something in the drivers or amp when I was setting everthing up due to the fact I am a Novice. IDK.

I know I should change my amp mounts for starters also, I am thinking of mounting the amps at an angle like so // OR I can mount the MRP-F600 under the drivers seat. I am starting to lean towards under the drivers seat just to get the poor amp mounted flat and out of the sealed trunk.

Thank you Alton and Impious for confirming that the impedance rise should NOT be a problem.

I will report my findings from the resistence/ohms tests.

[Impious 1,476]

I would suggest manually moving the cone up and down a good bit with a DMM on the terminals to see if there is a significant change.

[j-roadtatts 1,129]

I would suggest manually moving the cone up and down a good bit with a DMM on the terminals to see if there is a significant change.

Would change be good or bad? I ASSUME i can find what these should read in the specs of the drivers?

[altoncustomtech 773]

Change would be bad, VERY bad. If it's a 4 ohm driver it should read around 3.xx ohms DC. No matter what it reads, it shouldn't change from moving the cone.

[j-roadtatts 1,129]

Very Badd Sad. IT appears that I have cooked one voice coil. I Can only guess that its from to much power, But think that a clipped sig could of done the job also.

I pulled the two drivers out and right away could hear scratching in one of them. I hooked the DMM to each one.

The first one read 3.6-3.8 at rest and all over the place when I held the cone down or up.

The second one (the scratchy one ) read 1.6 at rest and when I went to move the cone it went to O.L. When I try to move the cone up it gets stuck real easy.

NOW I am stuck contemplating wheither to try and find a single driver and replace the blow one OR Find some drivers that will fit in my doors and can handle a little more abuse.

I know I am hard on things, thats why I try to over build things. My friends call me Doh-Zor if that explains anything. They will say the drivers where NOT Doh-zor approved.

I fell like a jack-ass right now but need to learn SO please be gentle on me.

I plan on contacting the company I bought them from and see what the warrenty covers. IDK IF the one driver could of had a defect but don't know. I guess thats the first place to start.

Another question: Is there something I can do to my door/enclosure that will help with power handling and cone control? Maybe CCF on the back wall or something?

[sefugi 166]

I guess that was not what you expected to find but now that you know you can move ahead...I did a search on the net and did not find any Doh-zor approved subs.

[altoncustomtech 773]

Man I really hate to hear that. Thing is, you may still be in good shape as far as the doors go. As you said earlier it could of all happened during the testing/tuning phase. If you don't notice the cone's moving as though they're out of control (should hear it as well) then most likely the problem was a clipped signal or something along those lines during the test/tune period. I would guess that the amp you have and the Aura's are a great match and the doors are working well as the enclosures for them and that the damage was induced while making adjustments. I would repair/replace the one bad Aura, leave everything just as it is and try running everything again since you're very close to being dialed in, and see how it goes. If you run into problems again then you/we should go over the possible causes and solutions.

[Impious 1,476]

Yup, definitely sounds like that 2nd driver is toast

Unfortunately there's nothing easy you can do to improve thermal power handling, which is apparently the issue you ran into given the VC sounds roasted.

[j-roadtatts 1,129]

One other thing that could of caused this would be the suround on the speaker hitting the grill and holding the coil in place and thus burning it. I noticed that the surrounds had grill lines on them and that the driver with the burnt coil had a big dent in the grill. The coil only feels burnt in the one spot on the outward stroke right about where the cone would of been hitting the grill.

I sent an email to the company I bought the drivers from asking about thier warranty policy. They have one more in stock SO if nothing else I will buy that one after testing that the other driver is still good. The good new is motor bolts on these drivers are on the outside SO after I hear back from them I will probably pull both drivers apart and take pictures for you guys to look at.

AND change the grill set up.

[ulrisa 26]

That sucks man! I'm sorry to hear it. Hopefully you can it get it warrantied.

[kirill007 52]

Have you looked at the gain setting?(it can change sometimes after you have set it)

Are you using any bassboost?

How do you set you're gains?

[j-roadtatts 1,129]

Have you looked at the gain setting?(it can change sometimes after you have set it)

Are you using any bassboost?

How do you set you're gains?

The gain is right over half, like 9/16. NO BOOST OR EQ. The cone looked very controlled over the last month as I have been keeping a close eye on the one I could see.

Everything honestly sounded great and was set very carefully before turning the gains up the last little bit.

I am starting to lean torwards the grill got bent in and then I listened with alot of excursion and BAM. To think back, It all started while I was listening to Six Feet Under, Demoing for a drummer friend. If you are unfamiliar with Six Feet Under, They are VERY drum heavy.

The speaker still plays at low volumes and only cuts the amp off when the coil reaches the bad spot.

[kirill007 52]

So u turned up the gain after u installed the midbass?(just asking)

[j-roadtatts 1,129]

So u turned up the gain after u installed the midbass?(just asking)

I installed everything and then tuned with the gain at around 1/4- 3/8. After I was cofortable with my settings I turned it up a little every few days until I reached about 5/8, then they started to overpower my highs so I turned it down a little.

[Sir-Lancelot 216]

Damn bro that sucks.

It sound like it was just seeing too much power. I am not 100%, but if the grill was hitting the driver and stopping it's stroke, that could have played into it. That VC had to move somewhere and if not up and down then side to side was the next choice.

I hope the manufacturer can work something out for you.

[altoncustomtech 773]

So u turned up the gain after u installed the midbass?(just asking)

I dunno if you've ever tuned a fully active system before, but it has to be done in that fashion. With the gains low, crossover, eq and level settings all have to be adjusted before setting the gains. Even then setting the gains is not done in the regular fashion either.

[j-roadtatts 1,129]

Once I pull them apart to inspect I will know further. I am waiting on the company to email back before touching the burnt one though.

I may pull the other one apart sooner, we will see. I am at work right now.

[kirill007 52]

So u turned up the gain after u installed the midbass?(just asking)

I dunno if you've ever tuned a fully active system before, but it has to be done in that fashion. With the gains low, crossover, eq and level settings all have to be adjusted before setting the gains. Even then setting the gains is not done in the regular fashion either.

Huh?

I know that you have to first set all the settings on the amp (except, gains, and don't use bassboost).

And after installing everything start to turn up the gain.(some do it by ear, other with a oscilloscope.)

But he said he turned up the gain bit by bit, maybe the last bit was too much for the driver to handle in free air.?