Crackling sound in all loudspeakers even after replacing old ones

[Michkin]

I recently purchased a 1995 Volkswagen T4 van and immediately noticed an issue with the audio system. At slightly higher volume levels, it sounded as if all four loudspeakers were broken. Upon inspection, I discovered that the previous owner had replaced the original loudspeakers with poor-quality ones and had installed two-way loudspeakers in place of the original tweeters on the dashboard and doors. Additionally, they had installed a cheap radio with a touchscreen.

One of the first things I did was to purchase a Continental DAB Radio with a retro look and a set of Alpine loudspeakers, including tweeters for the dashboard, 13" 2-way loudspeakers for the door, and a frequency filter for each side. I used the original wiring, except for the last part of the tweeters, where I attached a bit of wire for ease of use. Although the previous owner had done some wiring behind the radio, it did not appear relevant, and I fixed any poorly done wiring.

Unfortunately, after installation, the problem persisted. I tried changing the input polarity at the frequency filter, checked for broken wires, and played music from a USB or Bluetooth, but nothing helped. I also measured resistance for each wire connecting to the speakers and everything seems to be fine (meaning no broken wires). All four front loudspeakers sounded broken from mid-volume levels and up, meaning that I can barely listen to the radio while driving before the sound starts crackling.

The fact that all 4 loudspeakers are affected makes me thing that, if a broken wire is to blame, my bet is that it must be a ground wire, since it would be the only wire common to all loudspeakers.

I visited two local car audio workshops today, but they were unable to identify the problem. They suggested bringing the car in and checking all the audio wiring for a bad cable, but I like working on my car and I think I should be able to find the problem with a bit of help from you. What do you think could be the source of this problem?

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[1aespinoza 10+ year member]

What do you think could be the source of this problem

Does it crackle with the engine off?

 

[JohnPD]

Could be lots of different things. Bad ground, rca cable interference etc

 

[audiobaun 5,000+ posts]

Could be a poor ground on the HU. Id start there. Run a ground wire(14ga or 12ga0 from the HU ground wire to a solid cleaned off bolt or solid metal dash bar.Start with a solid ground on the HU

 

[hispls 5,000+ posts]

Disconnect all of the speakers from you source unit, pull one of the new speakers out and connect that directly to your head unit and see if you still have problems at that volume. If you have no problems connect one speaker at a time and test again.

It still could be your head unit is faulty or it could be you are need some sort of high pass filter on your components. You need to start removing variables to test everything by itself to isolate the problem.

 

[huberoy123 10+ year member]

Disconnect your alternator and see if the problem goes away. I had a similar issue and it turned out to be the alternator.

 

[Michkin]

Today I had the chance to take a look at this issue and did the following:

1) Checked that the problem is also present with the engine off. I assume this discards an alternator-related reason for the problem.

2) Measure the voltage at both (battery and key) 12V wires at the HU using the original ground cable. Voltage is ok.

3) Run a new cable from ground pin at HU to clean ground on the frame. Problem persists.

4) Tried with a different radio. Problem persists.

5) I could not connect the speakers directly to the HU for a reason: the signal goes from the HU to a frequency filter, and from them separately to the tweeters and the 2-way speakers at the doors. I guess I could try connecting the 2-way speakers directly to the HU, I may try that again tomorrow, but somehow I don't expect any difference.

It is quite annoying when you buy an old car and have no idea of what has been done on it that could be the reason for a current problem. It being a car from 1995 has a pretty simple audio system, but I am puzzled.

 

[audiobaun 5,000+ posts]

have you checked to see if this car has been in a flood/Flooded ? Could possibly be the ECU got wet and creating issues within the vehicles electrical system? Just throwing that out there as a possibility of a bad ECU?

 

[Michkin]

have you checked to see if this car has been in a flood/Flooded ? Could possibly be the ECU got wet and creating issues within the vehicles electrical system? Just throwing that out there as a possibility of a bad ECU?

There's no other electrical problem present in the car that could make me think of an issue of this kind. It's had only two previous owners and quite low mileage for its age. It runs smooth with no symptoms of an ECU problem.

I am tempted to dismantle the whole dashboard and check all connections, but that would be tedious.

 

[Michkin]

At the end I decided to take the dashboard out, since I also had to solve a problem with the heater core. Upon inspection, I could not find any faulty cable. I tried all possible combinations of loudspeakers (tweeters, door, rear, left, right) and the problem persists. I checked again that the battery feed is over 12V and that the key feed works as well. Both drop to some 11.3V when turning the ignition. I could also measure that the HU output -to both front and rear loudspeakers- is around 6.2V. Is this a good value? Both the HU and front loudspeakers are brand new Alpine.

I'm running out of ideas.

Maybe worth mentioning that while dismanteling the dashboard the radio stopped working due to a blown fuse. This fuse is shared between the radio and interior lights.