Earth under dash

[mr.tourette]

In the process of fitting an underseat subwoofer, all working fine in terms of powering up and playing audio but I'm getting some interference through the speakers on the same line out, gets louder and moves up and down with revs too

First thought is a bad earth but the point I'm using(glovebox mounting point) checks out on the multimeter although i'm not convinced its ideal..thing is I can't see any proper earth points under the dash so I'm a bit snookered ..I'm reading elsewhere there is a proper earth point in the passenger footwell but not found a pic..does anyone know if there is one under there that I'm missing...my other thought is to splice into the ground cable on the iso loom and try that but not really wanting to do that unless absolutely necessary...any thoughts on where this mysterious earth point is?? or for that matter any solid earth point

 

[BadgerDog]

[ref]mr.tourette[/ref], it could be a bad ground (earth), but it could just as easily be interference on the line in to the sub. If its routed too closely to any active wires they can become coupled. Something to consider as well.

 

[mr.tourette]

[ref]mr.tourette[/ref], it could be a bad ground (earth), but it could just as easily be interference on the line in to the sub. If its routed too closely to any active wires they can become coupled. Something to consider as well.

Thanks Badger, yeah i will go at it again, after a bit of research I also found what you have said about wires to close, this may be the problem as ive cable tied the power and rca where they first exit the sub to try and keep things neat, ill split all the wiring up later and try to run a shorter ground somewhere where there is a better chance of a good earth although to say options seem very limited is an understatement, Im struggling to find anything at all.. any thoughts on splicing into the ground cable on the iso loom?

 

[BadgerDog]

ive cable tied the power and rca

Undo this and reroute your wires before you do anything else. Power is very noisy, and is almost 100% certainly the cause here. It would explain the interference changing with engine speed as well... alternator introduces noise on the power side and that will change with speed.

As a general rule you want your power and audio lines as far apart as they can be. When I ran a new amp into my old Miata, I ran audio through the center of the car, and power along the left side (under the door) to keep them way apart.

If that doesnt do it you can try another ground/earth, but I suspect thats just fine. FWIW my degree is in electrical engineering, though I've mostly done software since graduating.

 

[mr.tourette]

ive cable tied the power and rca

Undo this and reroute your wires before you do anything else. Power is very noisy, and is almost 100% certainly the cause here. It would explain the interference changing with engine speed as well... alternator introduces noise on the power side and that will change with speed.

As a general rule you want your power and audio lines as far apart as they can be. When I ran a new amp into my old Miata, I ran audio through the center of the car, and power along the left side (under the door) to keep them way apart.

If that doesnt do it you can try another ground/earth, but I suspect thats just fine. FWIW my degree is in electrical engineering, though I've mostly done software since graduating.

Thanks for your inputbuddy is mich appreciated After splitting up the wiring with no change I had a good look at this excellent guide https://www.crutchfield.com/S-oedlkP7JeOx/learn/learningcenter/car/noise_suppressors_installation_guide.html

which led me to believe it was an rca isue.. turns out after speaking to the Amp manufacturers (Vibe UK) that they put a 3rd pair of rca leads on the loom for any such issues involving interference from the amp which effectively bypass the amp allowing a clean signal to the active sub.. plugged in there and all was well so the glove box earth was actually ok all along... shout out too to Vibe for their support on chat messenger even at the weekend

 

[flybobbie]

Cabin earth just behind the right panel next to the accelerator, underneath the insulation foam.

 

[Silverstar]

So Mr.Tourette how does the underseat sub sound? are you happy with it? Can you please post some photos of the install, perhaps on the other thread for continuity. I have an amp on order and am waiting for my Apple Car Play kit to arrive from China although there seems to be some shipping delays from there right now. When it comes that will be my next project for the audio / ICE.

 

[mr.tourette]

So Mr.Tourette how does the underseat sub sound? are you happy with it? Can you please post some photos of the install, perhaps on the other thread for continuity. I have an amp on order and am waiting for my Apple Car Play kit to arrive from China although there seems to be some shipping delays from there right now. When it comes that will be my next project for the audio / ICE.

Yes buddy I will get around to it at some point, I didn't really take many photos but will talk through it , it was actually incredibly simple in terms of wiring it in and only the interference issue slowed me down thinking I had a bad earth when it was fine all along, without buggering about with that it would only have been 1-2 hours max did you go for the vibe amp or one of the others you were looking at?

 

[Silverstar]

In the end I got a very good deal on a JBL A9004 which puts out 90W RMS x 4 at 4ohms. It's relatively compact so I can mount it in the same spot where the OEM amp for the upgraded Hifi goes. Since the Hertz woofers I got are rated at 90W RMS, this will do perfectly. I also managed to bag a second hand AudioControl LC6i LOC which should clean up the signal a little from the head unit and provide low level RCAs to the amps (JBL plus future sub amp). I am hoping to stick that somewhere under or behind the glove box.

 

[mr.tourette]

In the end I got a very good deal on a JBL A9004 which puts out 90W RMS x 4 at 4ohms. It's relatively compact so I can mount it in the same spot where the OEM amp for the upgraded Hifi goes. Since the Hertz woofers I got are rated at 90W RMS, this will do perfectly. I also managed to bag a second hand AudioControl LC6i LOC which should clean up the signal a little from the head unit and provide low level RCAs to the amps (JBL plus future sub amp). I am hoping to stick that somewhere under or behind the glove box.

Sounds like you are going all in

 

[Silverstar]

Sounds like you are going all in

Yep but still on a budget, be it slightly more than yours. :wink:

 

[Bodben]

I came here, rubbing my hands together looking forwards to a fruity story about a car with mysterious lumps of mud under the dashboard. Still a good thread though.

 

[BadgerDog]

[ref]mr.tourette[/ref], Glad you were able to get it sorted! Even if my advice didnt much matter in the end. ;-)