Troubleshooting issue where Subwoofer output seems to intermittently drop to half pwr

[knil]

I have a kicker ZX 750.1 and I was running a kicker solo baric L5 10 inch sub pre loaded in a truck sub enclosure (08TS10L54) it was a dual 2 ohm voice coil wired in series for a 4 ohm load. The setup ran perfect for about 3 years at which point I started to notice a slight distorted rattle coming from the sub at low volumes. I decided to upgrade to the new L7 10 inch Solo baric using the same truck sub enclosure that came with the pre-loaded L5. This time I went with the dual 4 ohm voice coil and wired it in parallel for a 2 ohm load to get more power out of my setup. After breaking the sub in for a few weeks, I started to crank it up and began to notice that it seemed like the sub was dropping to about half power from time to time. Since it was still under the seller warranty, I exchanged it for a new L7. Again, after a couple of weeks of breaking it in, I started to crank it up and the exact same problem started happening again. I get a new speaker smell in the cab of the car (not quite a burning smell, but maybe close) when it is cranking at what I am calling full power. I have checked the impendence of the sub and it is around 2.4 ohms which is exactly the same reading I was getting when it was brand new out of the box. I have even replaced the head unit thinking that maybe it was related to a bad preout (plus I wanted a new head unit anyway) and the problem is still there. I repair car amplifiers as a side hobby and I know that the common failure for amps is in the output transistors or the power supply transistors. I have taken the top off of the amp and everything looks good, the amp is not even getting that warm while it is playing. After I had thought the first L7 went bad, I made sure to properly set the gains of the sub and high amplifiers with the test tones and an oscilloscope just to make sure that I wasn't killing the new sub with too much gain. I will also admit when I had the original L5 running, I had the bass boost on the ZX750.1 cranked up before I realized had bad this was for the sub, before installing the new L7 I made sure to keep the bass boost at zero and rely only on the gain for adjustments (which is slightly between 1/4 and 1/2). Does anyone have any idea what may be going on or have experienced this type of behavior. To me, it almost seems like one of the 4 ohm voice coils is going in and out which would cause the amp to see the single 4 ohm load which would decrease the output but the sub reads around 2.4 ohms every time I put a meter on it. Thanks in advance for any help.

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[honkyg 10+ year member]

sounds like a voltage supply issue. a bad connection can be a choke point and hinder the amperage supply needed for your amp to operate properly when it tries to draw the current. might want to go and sand/wire brush, tighten, and reconstitute all of your connections.

if you havent done it already, the big 3 is in order.

 

[knil]

That is a good point and something that I did not think of. Also, I should probably go ahead and give you a description of my current power wiring. I have run about a 12-15 foot length of 4 gauge wire to a power distribution block that fans the power out to the Kicker ZX750.1 amp and the JL Audio XD400/4 amp and a 2 farad capacitor. I have also used about an 8 inch run of the 4 gauge wire from the distribution block to the power connection of the Kicker amp. My ground is set up with about a 4 or 5 foot run of 4 gauge wire (terminated to one of the seat belt bolts of the back seat of my Honda) to another power distribution block that feeds the kicker amp and the JL audio amp. Also there is a fuse close to where the power wire connection is made to the battery under the hood of the car and fuses in the power distribution block before it fans out to the amps. I am at work now, but I will take the connection loose and clean them up and re-terminate them. Again, thanks for the advice. I have been battling this issue for about 3 months and been lurking on forums to find information but finally bit the bullet and created an account here to seek help.

 

[honkyg 10+ year member]

well, youve got 120amp total draw for your audio components,.. im sure it's not loading all at once, but it can on high volume and bursts. we can factor in a loss of voltage and amperage over distance through the 4ga. power wire, 10% is acceptable in the electrical industry. personally, i always go overboard on my electrical just to be safe and keep my amps well fed,.. think of it as if you were trying to **** a milkshake through a straw,.. too small a wire is like using a capri sun straw or cocktail stir.

now, we also need to account for your alternator (provided it is stock) being given extra duty on top of powering your car's electrical. idk what you drive, but i can state that on average, alternators for passenger vehicles produce between 120-145 amp @14.4vdc, sometimes less, sometimes more.

i think you may be taxing your electrical system if youve got a large amount of electrically powered accoutrements in your vehicle.

once again, and i cannot stress it enough, do the big three if you havent already; 1 extra ground wire between engine block/head/alt case and batt, 1 extra ground between chassie and engine block/head/alt case, 1 extra ground between chassie and batt

 

[knil]

Ah, now I understand what you mean by the big 3. I have done a modified version of what you are calling the big 3. I replaced the factory wire between the engine block and chassis with a piece of the 4 gauge wire and I believe I replaced the factory wire between the negative terminal of the battery and chassis with a 4 gauge wire. I haven't done anything modifications with the one you describe between the battery and engine block. I will take your advice and double up on those 3 connection points. I drive a 2008 Honda Civic and I believe it's alternator may be rated around 100 amps. I am in the same thought camp as you about this being a power related issue, especially since I am now driving that kicker amp at 2 ohms instead of at 4 ohms. I did take a look at the connections between the amps and the power distribution blocks and everything looked tight. I will look at the connection point for my ground and see about sanding some more of the body where I make the connection for the amps. The only puzzling part of this problem is that speaker smell which keeps making me think one of the voice coils is trying to burn out, but since this is the second L7 with the same issues, I am inclined to remove the speaker from my fault isolation. Sorry you will have to forgive some of my nerdiness, I am an electrical engineer by trade, LoL

 

[knil]

I did a bit of research on the 2008 Honda Civic EX alternator and it looks to be rated at 80 amps. While doing a little extra troubleshooting, I decided to monitor the voltage as the car was running, and it was around 13.5-13.8 volts which seems a bit low. I wonder if after about 4 years of having the stereo has slowly taken its tool on the alternator, I will have to research some higher output alternators if this one is about to go bad. I had some corrosion on the battery post that I need to clean up and then do some more work on my big 3 (ran out of daylight for today) and then recheck the running voltage, but the alternator will need to be upgraded at any rate since it is under amperage for my system. I will continue to tweak and see if I can get to the root cause

 

[knil]

Wow, was researching High Output alternators that fit my Honda and the price range is salty, $400-$550 to upgrade to a 170-230 amp. I decided to recheck my gains last night since I noticed the new Kenwood head unit was 5V on pre outs whereas the pioneer I replaced was 4V. There was only marginal adjustments to be made on the JL which is powering my highs but the Kicker amp was up way too high. After tweaking the gains last night, I was disappointed with how little bass I was getting out of my sub. I started tweaking with the Eq and other setting on the head unit to bring the bass back up but it still wasn't quit where I thought the level should be. Then as I was driving home, the whole system decided to wake up and it was hitting hard. I'm still pestimistic and thinking this still may be an intermittent problem and expect it will be flat again tomorow, but we will see. I picked up some more 4 gauge wire to start tackling my big 3, Hope to find some time this weekend to perform that upgrade.

 

[honkyg 10+ year member]

Wow, was researching High Output alternators that fit my Honda and the price range is salty, $400-$550 to upgrade to a 170-230 amp. I decided to recheck my gains last night since I noticed the new Kenwood head unit was 5V on pre outs whereas the pioneer I replaced was 4V. There was only marginal adjustments to be made on the JL which is powering my highs but the Kicker amp was up way too high. After tweaking the gains last night, I was disappointed with how little bass I was getting out of my sub. I started tweaking with the Eq and other setting on the head unit to bring the bass back up but it still wasn't quit where I thought the level should be. Then as I was driving home, the whole system decided to wake up and it was hitting hard. I'm still pestimistic and thinking this still may be an intermittent problem and expect it will be flat again tomorow, but we will see. I picked up some more 4 gauge wire to start tackling my big 3, Hope to find some time this weekend to perform that upgrade.

this seems rather strange if its not a loose connection. hell, your voltage regulator might be taking a dump

 

[knil]

Yeah, I'm thinking the stock 70 amp alternator has been taking a lot of punishment over the years. I found a 170 amp alternator at alterstart for around $409 with shipping, I think I am going to go ahead and order it tomorow. I don't think the stock one will hold up much longer especially since the big amp is now driving a 2 ohm load instead of a 4 ohm load with the new L7 sub I recently installed.

 

[knil]

Well I took the plunge and ordered a HO alternator and installed it the other day. I also took this opportunity to do my "Big-3" as well. I noticed that the factory wire coming off the B+ side was not going directly to the battery but was instead feeding into a fused/relay box in the engine compartment before feeding back to the battery and then another heavy gauge wire was running from the battery to what I guess would probably be the starter. I decided to run a new 4 gauge directly from the B+ to the battery as well as reconnecting the factory connection from the fuse box to the alternator. I just soldered the wire coming back out of the fuse box to the one that was running to the starter. It would seem to be fancy way of splitting the audio system power from the rest of the car's electrical system except for the fact that the new 4 gauge wire run between the battery and the alternator creates a direct short back to the factor connection going to the fuse box. I can see why some people choose to go with an inline fuse between the alternator and battery since it looks like the original factory connection was providing this protection previously. I already had 4 guage going between the negative battery post connection and the body and I made another 4 gauge jumper between the body of the car and the engine. I expect that will get a few virtual fist bump since I can now claim to have both feet in the "big 3" club as well as the HO alternator upgrade club. With all that said, back to my original issue that lead to the creation of this post. I suspect the stock alternator was in its final death spasm from about 5-6 years of abuse. After performing the upgrade above, I had forgot how bright the headlights must have been back before installing the system, and it is refreshing not having other drivers flash their headlights at you because they you were doing the same to them during loud bass hits, LoL. Since I had to take the battery connections lose during the upgrade, my head unit reset back to it's factor settings and I have been trying to go back through and re-tune the sound settings, but I have noticed that I am getting much better performance from my audio gear, at least the audio system and car electrical system are no longer having to compete for amperage anymore. I will continue to monitor and tune the setting and update the thread if I start experience the intermittent power output issues.