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    Single sub phase problem?

    Howdy, I have not done a car audio install since the mid 90's, but I used to do quite a few. My girlfriend decided that she wanted a little thump in her 09 Mazda 3, and I found some used equipment cheap from my cousin, and bought it to install for her, however I am having a weird issue I was hoping for help with.

    First, here is the setup:
    • 09 Mazda 3 stock (non bose) head unit.
    • Line out converter (either the wiring diagrams I found were backwards, or I read it backwards, but the LOC is tapped to the front speakers instead of the rear for now.)
    • Pioneer GM-5500t (it is running bridged)
    • 12in Kicker CompS sub in a sealed enclosure

    After much struggling and cursing, I got the power, amp remote, and RCA cables run and tucked in. I also had to find a good ground when EVERYTHING in the **** trunk is painted/coated/covered in some way, and I only had a short ground wire.

    As it stands it plays, and the grounding is good as I have no clicks/whine with the motor on. I was very happy about this!

    The amp has the built-in lowpass crossover on and set at ~250hz.

    The problem is this. The bass is extremely weak. If I adjust the balance all the way to the left or right, it thumps, but in the middle it is very weak. Now from past experience (at least with non-bridged setups) between any two speakers on opposite channels (l/r or front/rear), if adjusting to one of the speakers increased the volume, it was a phase problem. Either a speaker was wired in revers polarity or the input signal on one channel was reversed somehow.
    • At any rate, thinking it may be a phase issue, this is what I have tried, and the results:
    • Reverse the input polarity of one side of the LOC (No change)
    • Remove one RCA (still weak in the middle, when balanced to the removed side no sub, to the other side it rocks).
    • Reversed the polarity of the sub (I have not been in the box so it could have been wired wrong, so I reversed it at the amp, thinking maybe it is out of phase with the rest of the speakers somehow- but also knowing if it was, balance adjustments shouldn't make it louder) (Results, no change)

    There are a couple of other things I could try, but my mind is saying they will have no difference, and that is, reverse the inputs to -both- left and right on the LOC, wire the LOC to the rear speaker outputs.

    I feel like in my lack of recent experience I am missing something very simple but I do not know what. Any help is much appreciated, as I am getting very frustrated with this.
    Last edited by BTG; 07-31-2013 at 03:58 PM.







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    Re: Single sub phase problem?

    OK so...
    1) this is your girlfriends car, so your a$$ is on the line
    2) It sounds like you accidentally swapped polarity on *one* of the speaker inputs (left or right) going into the LOC. What is happening is that the bridged amp is mixing the right and left signals into a mono mix into the sub. Because one channel is out of phase they actually cancel each other out when centered.

    SOLUTION: Simply swap the (+) and (-) of *one* of the speaker inputs to the LOC. Either the left-front or the right front. Once it is working as expected from a balance standpoint, you may then want to go to the sub speaker leads and see which polarity gives the strongest hit.




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    Re: Single sub phase problem?

    OK so...

    1) this is your girlfriends car, so your a$$ is on the line here.
    2) It sounds like you accidentally swapped polarity on *one* of the speaker inputs (left or right) going into the LOC. What is happening is that the bridged amp is mixing the right and left signals into a mono mix into the sub. Because one channel is out of phase they actually cancel each other out when centered.

    SOLUTION: Simply swap the (+) and (-) of *one* of the speaker inputs going into the LOC. Either the left-front or the right front. Once it is working as expected from a balance standpoint, you may *then* want to go to the sub speaker leads and see which polarity gives the strongest hit to make sure the sub is firing with the correct push-pull phase in relation to the bass signal.




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    Re: Single sub phase problem?

    Thanks for your input. Actually, switching the polarity on one LOC input was the first thing I tried, with no change. It had (and still has me baffled).

    However, I did find a fix. I did not want the sub wired to the front, so I switched it to the rear outputs, and all is well. I tried unbridging the amp first, just in case it was something with the amp, but that was not helpful either.

    Thanks again for your input.




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    Re: Single sub phase problem?

    Quote Originally Posted by BTG View Post
    Thanks for your input. Actually, switching the polarity on one LOC input was the first thing I tried, with no change. It had (and still has me baffled).

    However, I did find a fix. I did not want the sub wired to the front, so I switched it to the rear outputs, and all is well. I tried unbridging the amp first, just in case it was something with the amp, but that was not helpful either.

    Thanks again for your input.
    My guess is one of the wires you tapped into for the LOC wasn't what you thought it was. With the symptoms, the ONLY thing it could be is the LOC is faulty or you tapped the wrong wires and one side is out of phase.

    Typically people tap the rears anyway so I guess it all worked out AND the fact that that worked proves that the LOC isn't the culprit




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    Re: Single sub phase problem?

    set your lpf to 80 not 250




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    Re: Single sub phase problem?

    Quote Originally Posted by hispls View Post
    My guess is one of the wires you tapped into for the LOC wasn't what you thought it was. With the symptoms, the ONLY thing it could be is the LOC is faulty or you tapped the wrong wires and one side is out of phase.

    Typically people tap the rears anyway so I guess it all worked out AND the fact that that worked proves that the LOC isn't the culprit
    @hispls, I agree that it had to be a faulty LOC or switched polarity on one input. I also agree that it should be tapped to the rears, which it is now so all is good. Thanks!

    @Side Show, I have lowered the LPF to around 100. I want it a tad higher than 80, as I am turning the bass down some in the stock head unit to help prevent distortion in the stock speakers, and compensating with the gain on the amp, to balance it out. When reducing the head units bass, to my ear, it seemed to cut at about 100-120, so I need that range filled some by the sub.

    If you or anyone else has better ideas (aside from going all out and replacing the head, unit, stock speakers, adding another amp and x-over, thats just not in the budget!!) I am all ears and appreciative of any input.




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