2CH amp - low output to 1 channel

[3viley3]

Power not distributing evenly (full power to one sub, other sub is moving but hardly noticeable)

Amp: Rockford Fosgate P8002

200W x 2 @ 4-Ohms RMS

400W x 2 @ 2-Ohms RMS

800W x 1 @ 4-Ohms bridged RMS

Subs: Two 12" Punch

P3L-S12's.

4-ohm load

Amp is set to Low Pass at about 50Hz.

No external crossover/EQ.

Firstly, system is 4 years old and sound output hardly has changed.

I first disconnected both subs and switched right>left and then one at a time. Both subs fired fine with one connected to either channel. Strange was when I reconnected back the way it was before, the nominal movement switched from the right sub to left with everything the way it was before.

I've proven that both channels work when only one sub is using either the left or right. It's when both channels are being used is when one of the channels doesn't put-out at full capacity. Can this be easily resolved or is this something that requires the internal components to be diagnosed? Thanks for any help.

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[funkyab 10+ year member]

out of phase perhaps. How have you set your levels? DMM?? What happens in bridged mode?

 

[3viley3]

In regards to phasing, the box is a sealed 2 chamber so they shouldn't be affecting one another. I also don't see how a mis-wire could be the culprit since after I switched the small-firing sub from left channel to right and secluded it from the other sub, it worked fine. To add to that, after I disconnected, tested and then put them back the way it was...the problem switched sides.

I'm no expert by any means and I need to take a day when I have more time and really take a closer look at this before I determine it's a voltage issue or internal problem with the amp. However, I find it strange that the problem could switch sides when they are connected now the same as they were. To simplify.....

The left channel surround was moving 1/16" and the right channel was moving about 1/2" at normal listening. Then when I tested each sub individually on each channel, and then reconnected them. They switched movement distance (left to right and visa-versa).

If this is impossible and everyone attests to this, then I admit that I may have made a mistake when I reconnected everything. If not, could it be any sort of electrical problem with the amp? I work in computers and I know that electronics act strangely sometimes.

My levels are set as such:

Amp is set to Low Pass at about 50Hz. The gains are a little less than halfway.

Have never attempted bridging. Maybe I should? A mono-bridgable amp and two 4ohm subs...is that ideal? That would bring the speakers down to 2ohms and the amp at 1ohm right? If so, that sounds do-able.

No external crossover/EQ besides the included, trademarked, Punch Bass EQ, that I actually use and I hate to love it. (maybe that?)

Head unit is an Alpine CDA-9830. The "MediaExpander" is not on but the Sub level is set to +9 (I've used that setting for years). The EQ is set in the middle. The head unit is powering rear MB quart 4X6's

I also have a Fosgate P4004 4-channel connected to front component 6 1/2's. I don't exactly know why the 4 channel only powers the components and not the MB quarts because I had a shop install the 4 channel and the front and rear mids a while after the subs were put in.

Anyway, that's all I have for now. Is there a FAQ somewhere to help me with using the DMM? My experience with them is mainly for PC's and gaming consoles, I haven't used one in a 12v environment.

As always, thanks a lot and I'm sorry for the windy response.

 

[kmanian 5,000+ posts]

Are the subs DVC, if so I think you have one of them wired unlike the other, or I guess I am saying check he resistance of the drivers individually as the amp sees them.

 

[funkyab 10+ year member]

check the resistance on both of your subs... if one differs greatly from the other this would easily explain your problem. I am guessing this would be the issue.

as far as using a DMM to set your levels,, go the the amplifiers section of this site, go into the stickys and go to the amplifier/gain setting tutorials or go here. http://mobile.jlaudio.com/support_pages.php?page_id=143

 

[3viley3]

Are the subs DVC, if so I think you have one of them wired unlike the other, or I guess I am saying check he resistance of the drivers individually as the amp sees them.

Good question but no, they are SVC.

 

[funkyab 10+ year member]

still check the resistance of the drivers and see how close they are.

 

[3viley3]

check the resistance on both of your subs... if one differs greatly from the other this would easily explain your problem. I am guessing this would be the issue.
as far as using a DMM to set your levels,, go the the amplifiers section of this site, go into the stickys and go to the amplifier/gain setting tutorials or go here. http://mobile.jlaudio.com/support_pages.php?page_id=143

Thanks, I checked out the link and that helps a great deal. One question though...

I must apologize right away for my lack of knowledge but I wanted to be clear. I would actually be testing the amp speaker output with the DMM on the + (no speaker) and the - with the speaker plugged in?

Either way, if the resistance is for some reason, different, how can that be resolved?

Thanks again.

 

[funkyab 10+ year member]

No.. when you set your levels you do not have the speakers plugged in..

when you test the resistance of your drivers you set the DMM to read ohms and put the testing points on the pos and neg of the sub..

2 totally different things.

 

[3viley3]

No.. when you set your levels you do not have the speakers plugged in..
when you test the resistance of your drivers you set the DMM to read ohms and put the testing points on the pos and neg of the sub..

2 totally different things.

Understood. The wording and the animation were contrasting since it showed the negative of the speaker still connected to the amp. Confusion on my part.

I'm going to do some more testing now that you've given me more to work with. I hope I can append to this later with what I found. Again, thanks a lot for the help and time.