Car audio questions from bad sound from subwoofers... Bass is different, Electromagnetic Interfence?

[BassErex]

Update 2: Last time after disconnecting the equipment from battery and all instalation of the car, (welding exhaust). And instaled back all powers (all wires are tight, no slack) I've noticed a bit more of a drop voltage on amps and very small power of subs. Oh ok, my volt meter readed 13,8v, so i caught a multimeter and test voltage on amp, I noticed every few seconds voltage drops to 11volts! it is possible that the drops are lower, but reading of multimetter is not fast... Maybe that's been my problem all along. My subs is now wired to 0,5 ohm on amp. At higher wirring (2ohm) i not see this problem on amp terminalls..
On my battery voltage is strong, so problem is only on wires.

Check out this article on Parallel grounding, maybe it will help!

https://www.bestcaraudio.com/car-audio-myths-you-cant-ground-a-car-audio-amplifier-to-the-battery/

I ordered the cables and that's what I want to do it
I suspect a problem of wires ground, but i dont know why...
This time I will try to do as short as posible wires ground to amp,
I give grounds parrael 2x 50mm2 to chasis and of this same point chasis to amps, but 70mm2 wires x2

 

[BassErex]

Update 3: New and more ground point (PARAEL) not working... First start play my sound system, bass not bad, and not 100% good, the bass gone after 10 minutes. Ground wires 2x shorter, but now power wires 2x longer.
Below in the photo you can see the tension on the music play, tension on amplifier ground, in peace is about 0,5v, on music jumps from 0,050v to 1,4v. Reading from: GROUND TERMINAL AMP AND BODY AMP (SCREW)
In addition, I observed two phenomena:
1. FIRST Play system car audio after Test new grounds point: Source AUX/BT nice signal rca (because something else?)
volume 22 and full power audio, after next engine start: i must set volume about 26-27 to get this same. So, RCA signal LOSS?
2. I have on my BITMAT ab25 a 0,2-0,3 voltage, WFT? Why?

 

[BassErex]

Hello back, For those who are also looking for a problem of sh*t bass, after such a long time of fighting,
I come to a conclusion that the problem is with the electricity power...
This issue is very very rare, but this is a traditional problem with Connection Lossing.
I still don't know what's going on (I think current is loosing in 100% good wires LOL?)
I changed cables, checked all connections, grounds points, fuses itp... But no loose conections, all are tight!
Everything came out since I have a hifonics amplifier, who work at 0,5 ohms, i see BIG VOLTAGE DROPS And Voltage boost! LOL
my alt is charging at 14,8v but on amplifier terminal i see volts 11 to 16,5 volts! its to much... the amplifier excitation can give above 1volt voltage drop! or much more!
This was not visible on any other amplifiers!
As for the sound quality, loss bass, I think the amplifier draws voltage (GROUND) From Rca, what causes Head unit Mallufunctions and different RCA OUTPUT voltage, yesterday i have Loud sound on 19 volume on AUX/BT, Wchich sometimes i must put about 25-26volume on my head unit to have this same loud from Music, or power.
I'm writing this for those who are also looking for a solution, because it's possible that this year I won't try anything else...
However, I will try the following things:
- Supercapacitors 1 pack 500f (6x 3000f) and max 60cm per wire SUPERCAPACITORS->AMP. More bigger wires, or much more to amp (Now i have 4x 50mm2, i try 8x 50mm2 or 8x 70mm2 wires)
If this doesn't help, I don't know what to do...
Voltmeter Which I have connected to the amplifier terminals, dont see this BIG voltage drops.
For those who want to see what it looks like on video. On vid Sound like Great, but on real Sound like bad...