Troubleshooting Help Needed

[ahas83]

Hi everybody. I am new on this site but have been reading many posts over the last month to get my system to work properly. I have tried a lot of things to nail down any potential fixes but cannot seem to find anything. Hopefully, you guys can help me narrow down my issue.

I recently installed a LC2i, JL JX500/1D amplifier, and a 12W3v3-4 subwoofer – 300W RMS at 4ohms in a sealed box installed in the back corner of my car. There is also a harness in between the factory speaker wiring harness connector and stock amplifier to tap into the underseat ‘subwoofers’ (but really mid-bass speakers) in my 2011 BMW M3 and connected to the LC2i speaker inputs.

The issue is the sound output from the subwoofer is not much unless I turn it up.

Things I have tried:

• Measured for voltage drops by measuring DC voltage with car running, playing a 50Hz tone at high volume at battery (~14.4V), voltage at amplifier (~14.4V), voltage at LC2i (~14.4V), they all really fluctuate from 14.35V to 14.4V, so there’s good grounding and no voltage drop or increased resistance in my connections
• Measured AC voltage of each underseat subwoofer at the harness and at the LC2i speaker input while playing a 50Hz tone at high volume to see if there is voltage drop due to a loose connection or incorrect wiring, but there’s no voltage drop there either. Both were at 31.1VAC under load.
• Replaced my RCA cables also since they seemed loose, but no change. Checked polarity of wires coming into LC2i to make sure I did not switch + to -.
• My logic tells me since iPad to amplifier played well, my issue is either the wiring harness, or LC2i or RCA cables. I connected a 3.5mm headphone jack to RCA cables and played music through my iPad. At pad’s max volume, I was getting ~8VAC with the 50Hz test tone, and when I played music thru my apple music app, subwoofer was sounding better, which lead me to believe, my problem is not the amplifier.
• Playing the same track through my USB port, I have to have the volume up ~40-50%-ish to get the same 8VAC I got with the iPad
• I set my gains initially using the DMM method, played 50Hz tone and set LC2i until the ‘maximized’ light went off, then set the amplifier sensitivity until I got ~34.6VAC at amplifier speaker output, but I felt like bass at low end/low volume was not good at all with the gains set up to this method.
• I increased the gains at both the LC2i and amplifier to get some more low end/low volume bass, but from reading countless threads on the BMW forums, my gains were much higher than what most people had theirs set to. Right now, LC2i gain is set to roughly 12 o'clock using main output, and amplifier set to 9 o'clock. I've also read that to adjust gain at LC2i and keep amp gain at minimum/or slight increase on the BMW forums and that's worked pretty for most people.
• I have also measured resistance at the subwoofer terminals to check if subwoofer was bad and got 4 ohms, I checked all wiring for continuity, and all seems good. I checked for loose wires in the wiring harness and pushed them all in to make sure its tight.
• Only thing I can think of is that either the wiring harness or LC2i are bad, but I cannot seem to identify what is wrong where.

I thought about getting a new harness and trying that since I bought the entire setup used on the BMW forum, but I would rather not just throw money at parts hoping for a solution. Unfortunately, there does not seem to be many people doing audio upgrades on these cars and the Audio section of the forum is pretty quiet.

Perhaps my amplifier power is not enough since its 300W RMS at 4 ohms, but at the same time shouldn’t 300W give ‘enough’ power, at least to determine if system is working properly?

Is there any other troubleshooting or testing I can do to pinpoint the root of my issues? Any tips or advice is appreciated!

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[Lasherž]

Hi everybody. I am new on this site but have been reading many posts over the last month to get my system to work properly. I have tried a lot of things to nail down any potential fixes but cannot seem to find anything. Hopefully, you guys can help me narrow down my issue.

I recently installed a LC2i, JL JX500/1D amplifier, and a 12W3v3-4 subwoofer – 300W RMS at 4ohms in a sealed box installed in the back corner of my car. There is also a harness in between the factory speaker wiring harness connector and stock amplifier to tap into the underseat ‘subwoofers’ (but really mid-bass speakers) in my 2011 BMW M3 and connected to the LC2i speaker inputs.

The issue is the sound output from the subwoofer is not much unless I turn it up.

Things I have tried:

• Measured for voltage drops by measuring DC voltage with car running, playing a 50Hz tone at high volume at battery (~14.4V), voltage at amplifier (~14.4V), voltage at LC2i (~14.4V), they all really fluctuate from 14.35V to 14.4V, so there’s good grounding and no voltage drop or increased resistance in my connections
• Measured AC voltage of each underseat subwoofer at the harness and at the LC2i speaker input while playing a 50Hz tone at high volume to see if there is voltage drop due to a loose connection or incorrect wiring, but there’s no voltage drop there either. Both were at 31.1VAC under load.
• Replaced my RCA cables also since they seemed loose, but no change. Checked polarity of wires coming into LC2i to make sure I did not switch + to -.
• My logic tells me since iPad to amplifier played well, my issue is either the wiring harness, or LC2i or RCA cables. I connected a 3.5mm headphone jack to RCA cables and played music through my iPad. At pad’s max volume, I was getting ~8VAC with the 50Hz test tone, and when I played music thru my apple music app, subwoofer was sounding better, which lead me to believe, my problem is not the amplifier.
• Playing the same track through my USB port, I have to have the volume up ~40-50%-ish to get the same 8VAC I got with the iPad
• I set my gains initially using the DMM method, played 50Hz tone and set LC2i until the ‘maximized’ light went off, then set the amplifier sensitivity until I got ~34.6VAC at amplifier speaker output, but I felt like bass at low end/low volume was not good at all with the gains set up to this method.
• I increased the gains at both the LC2i and amplifier to get some more low end/low volume bass, but from reading countless threads on the BMW forums, my gains were much higher than what most people had theirs set to. Right now, LC2i gain is set to roughly 12 o'clock using main output, and amplifier set to 9 o'clock. I've also read that to adjust gain at LC2i and keep amp gain at minimum/or slight increase on the BMW forums and that's worked pretty for most people.
• I have also measured resistance at the subwoofer terminals to check if subwoofer was bad and got 4 ohms, I checked all wiring for continuity, and all seems good. I checked for loose wires in the wiring harness and pushed them all in to make sure its tight.
• Only thing I can think of is that either the wiring harness or LC2i are bad, but I cannot seem to identify what is wrong where.

I thought about getting a new harness and trying that since I bought the entire setup used on the BMW forum, but I would rather not just throw money at parts hoping for a solution. Unfortunately, there does not seem to be many people doing audio upgrades on these cars and the Audio section of the forum is pretty quiet.

Perhaps my amplifier power is not enough since its 300W RMS at 4 ohms, but at the same time shouldn’t 300W give ‘enough’ power, at least to determine if system is working properly?

Is there any other troubleshooting or testing I can do to pinpoint the root of my issues? Any tips or advice is appreciated!

I also own the LC2i and something to be aware of is that the trubass and acubass knobs can be very confusing. Once it's setup at high volumes you'll need to redo the whole setup for low volumes using the bass threshold knob and acubass knob. What this does is when the volume is low it plays the normal signal but when it's high it plays a slightly amplified signal in the bass range. The reason is that cars lower the bass output as the volume goes up to spare the cheap speakers from getting blown and the cheap internal amp in the head unit from clipping.

It seems like you're doing a good job in troubleshooting it on its own, but yeah the LC2i requires a bit more thought than usual.

As for your power output at the high end not being very much, well the sealed box is going to have a lot to do with that. 300W isn't very much, particularly on a sealed enclosure. You'll never get mirror-shaking bass with that unless you get much more powerful. With 300W ported is the more common box since it makes due with a lot less power and can sound quite formidable. The noise output depends on a lot of things with your system including the car's cab volume, but when you have a small sealed enclosure with only 300W my expectation isn't very high, and it's pretty likely that yours was maybe a little too high.

For context, I have a 1200W RMS amp powering a Hertz SX 380D in a sealed enclosure at the manufacturer recommended dimensions. It's very accurate, very high quality sound, but very low volume. Even at 1200W near clipping there's hardly a thud, whereas my old setup with 2 12's and a 500W amp in a ported enclosure would shake the car probably twice as much even at less than half the power.

 

[ahas83]

Hi Lasherž - thanks for your response. Couple comments:

1) I have the subwoofer connected to the 'main' output of the LC2i, and am not using Accubass - at high volume, sub output is good, and I typically dont listen to music very loud. My issue is i have low output from sub at low volume. When playing music at volume levels i typically listen to, i am getting ~4-5VAC at the amp speaker outputs which is not much power. The reason I installed the subwoofer was because I wanted more bass at lower volumes.

2) I think you're right on a couple things, my expectations may have been too high, also my amp is not adequate for my setup, especially since the subwoofer is 4 ohms and needs more speaker output voltage at the amp. My car is also insulated very well from factory, therefore i am also looking at bass output at the subwoofer and think it should be better.

Since my last post, i removed the harness, made sure all pins were on tight, checked continuity from end to end with a DMM, replaced the wire from amp to sub since i found a small kink in the wire insulation and a few broken strands, also re-checked voltages with a 50Hz test tone, rechecked for voltage drop.

Is there anything else i am missing or can try? Can this be fixed by increasing the gain on the amp? I currently have the LC2i set at roughly 11 o'clock, and amp at 9 o'clock.

 

[blazian87 10+ year member]

it's not your LC2i that's the problem. Your expectations are too high for the equipment you have. You need to either upgrade your amp or build a new custom enclosure or both. Sealed boxes do poorly in efficiency so if you want to keep it sealed, you're gonna need to double or triple your power to make it worthwhile. If you were to only choose one thing to upgrade that would make the biggest difference, it would be the enclosure. My very first system consisted of a 300w amp and going from a sealed box to a custom ported box was a big game changer. Every friend that I convinced to switch to a ported box saw a huge difference in output and deep lows from switching enclosures alone.

 

[Lasherž]

Hi Lasherž - thanks for your response. Couple comments:

1) I have the subwoofer connected to the 'main' output of the LC2i, and am not using Accubass - at high volume, sub output is good, and I typically dont listen to music very loud. My issue is i have low output from sub at low volume. When playing music at volume levels i typically listen to, i am getting ~4-5VAC at the amp speaker outputs which is not much power. The reason I installed the subwoofer was because I wanted more bass at lower volumes.

2) I think you're right on a couple things, my expectations may have been too high, also my amp is not adequate for my setup, especially since the subwoofer is 4 ohms and needs more speaker output voltage at the amp. My car is also insulated very well from factory, therefore i am also looking at bass output at the subwoofer and think it should be better.

Since my last post, i removed the harness, made sure all pins were on tight, checked continuity from end to end with a DMM, replaced the wire from amp to sub since i found a small kink in the wire insulation and a few broken strands, also re-checked voltages with a 50Hz test tone, rechecked for voltage drop.

Is there anything else i am missing or can try? Can this be fixed by increasing the gain on the amp? I currently have the LC2i set at roughly 11 o'clock, and amp at 9 o'clock.

Yeah 4-5V isn't very much at all. It should be closer to 34V @ 4 ohms to get 300W. Once you're at 34V though I think unfortunately that may be as good as it'll get with that setup. I mean, there's a huge difference between 4-5v and 34 so you'll see an improvement. Another thing you can try is turning the subwoofer around or moving it to find the sweet spot just to make it a little louder to your ears.

When setting gains preferentially set the LC2i first until it's near clip, then set the amp. The goal is to get as strong of a signal as possible to avoid interference. Only lower the gain on the LC2i if the minimum gain position on the amp is still too powerful or if you want to do a little acubass restoration, then you'll just do it the same way, until it clips then turn the gain down a little (with test tones).

 

[ahas83]

the sealed enclosure is a custom enclosure that fits into the back corner by the tail lights which i like since i still have all my trunk space and cant move it around the trunk either. I will get a more powerful amp.

I tuned the LC2i to near clipping, and amp to 34VAC with the test tones, but was getting the 4-5VAC (low bass) playing music at low volume, which is why i thought something was wrong. After going down all the rabbit holes and making sure every connection and measurement was correct, I realized it was my expectations that were wrong lol.

Another thought i've been having - with my 'goals' from this system, would tuning with -3 or -6dB test tone be better? right now I am using a 0dB 50Hz tone.

Thanks for your help guys!

 

[Lasherž]

the sealed enclosure is a custom enclosure that fits into the back corner by the tail lights which i like since i still have all my trunk space and cant move it around the trunk either. I will get a more powerful amp.

I tuned the LC2i to near clipping, and amp to 34VAC with the test tones, but was getting the 4-5VAC (low bass) playing music at low volume, which is why i thought something was wrong. After going down all the rabbit holes and making sure every connection and measurement was correct, I realized it was my expectations that were wrong lol.

Another thought i've been having - with my 'goals' from this system, would tuning with -3 or -6dB test tone be better? right now I am using a 0dB 50Hz tone.

Thanks for your help guys!

Music should be higher than that, I think you should try using the bass side instead of the main side. I mean that's its main advantage besides high signal integrity from other cheap LOCs. I have a feeling that you're bumping up against a frequency response issue with the main circuit because that's incredibly low. The difference between my sine wave tests and music utilizing the same beats is like 90% not 15% Alternatively your test tone is clipping right from the head unit or something. That's definitely not correct. Then again I have a min-max true rms multimeter, you might be getting issues measuring the music. I don't know if that could cause such a large dependency. Does your meter measure maximums over time? Otherwise the odds of you catching a peak on the display are very small.

 

[ahas83]

I will try the bass output. My DMM is just basic, rms.

Also to clarify, the 4-5V i got was at lower volumes that i normally listen to music at, not at the same volume i used to set my amp gain. Not a true apples to apples comparison.

What music file do you use for your sine wave comparison? I can try the same to see if i get similar results.

 

[Lasherž]

I will try the bass output. My DMM is just basic, rms.

Also to clarify, the 4-5V i got was at lower volumes that i normally listen to music at, not at the same volume i used to set my amp gain. Not a true apples to apples comparison.

What music file do you use for your sine wave comparison? I can try the same to see if i get similar results.

I use the 0dB test tones from Kicker on this site:

KICKER | Test Tones

KICKER produces high-performance car audio, vehicle specific solutions, marine audio, home and personal audio, and power sports products since 1973.

www.kicker.com

50hz usually

If you're unhappy with the bass on normal music and your test tones are super volumous, maybe it's because the source you're setting the gains with is significantly louder than the source you're playing music from. You should be very close to hitting clip points in bassy songs with the same volume as the tone, so 2 or 3 extra ticks on the volume would usually start blinking the lights, at least on my amp.

 

[1aespinoza 10+ year member]

I use the 0dB test tones from Kicker on this site:

KICKER | Test Tones

KICKER produces high-performance car audio, vehicle specific solutions, marine audio, home and personal audio, and power sports products since 1973.

www.kicker.com

50hz usually

If you're unhappy with the bass on normal music and your test tones are super volumous, maybe it's because the source you're setting the gains with is significantly louder than the source you're playing music from. You should be very close to hitting clip points in bassy songs with the same volume as the tone, so 2 or 3 extra ticks on the volume would usually start blinking the lights, at least on my amp.

I agree that it is the source going to the loc where the issue lies. Ahas83 said that the underseat subs were more like midrange. I think to protect said midrange/woofer setup, the amp does not feed them a signal that drops down to 50hz, and if it does, it would probably be anemic. Also, I thought most tuned sub amps with an 80hz signal and voice amps with a 1khz signal.

 

[Lasherž]

I agree that it is the source going to the loc where the issue lies. Ahas83 said that the underseat subs were more like midrange. I think to protect said midrange/woofer setup, the amp does not feed them a signal that drops down to 50hz, and if it does, it would probably be anemic. Also, I thought most tuned sub amps with an 80hz signal and voice amps with a 1khz signal.

Yeah that's an issue I'm dealing with in my car too, but I think maybe he's running a test tone through the ipad instead of through the head unit which is very likely to be the problem. I say even go as far as burning a CD and playing it in the car with the test tone if you need to.

The "correct" tuning frequency will depend on impedance so it's dependent on the enclosure and the driver which tone is the best to use. The best way to find it though is to just play a lot of them and figure out which one gives the most voltage and use that. Between 40 and 80 will usually be the right spot. 60hz is the most accurate for non-true rms meters.

When you say you measured 4 ohms at the subwoofer, that's actually too high for a 4ohm sub. Impedance goes up as the subwoofer plays, but a DMM can't measure that. So 4 ohms is actually more similar to 5 or 6 ohms impedance on speakers. The resistance DMM value is usually somewhere between 2/3 and 3/4 the impedance value.

 

[1aespinoza 10+ year member]

Yeah that's an issue I'm dealing with in my car too, but I think maybe he's running a test tone through the ipad instead of through the head unit which is very likely to be the problem. I say even go as far as burning a CD and playing it in the car with the test tone if you need to.

The "correct" tuning frequency will depend on impedance so it's dependent on the enclosure and the driver which tone is the best to use. The best way to find it though is to just play a lot of them and figure out which one gives the most voltage and use that. Between 40 and 80 will usually be the right spot. 60hz is the most accurate for non-true rms meters.

When you say you measured 4 ohms at the subwoofer, that's actually too high for a 4ohm sub. Impedance goes up as the subwoofer plays, but a DMM can't measure that. So 4 ohms is actually more similar to 5 or 6 ohms impedance on speakers. The resistance DMM value is usually somewhere between 2/3 and 3/4 the impedance value.

Valid point.