Little dog playing up again. This time it's rustling noises from just one speaker.

Little Dog

A2OC Donor
European-Union
A new development that completely has me beaten and I don't know where to start. When the engine is running there is a rustling noise from the N/S rear door speaker. It appears worse when the car is moving but that could be because it is distracting me from driving:


It is just the one speaker and the radio is switched off. Any ideas, just being advised where to start would help. Thank you.
 
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Very much sounds like electrical interference noise to me. I’m a bit of a novice but I believe that when rear speakers are present they a driven off a separate amplifier which is located in the drivers side foot well. I am making the assumption that you don’t have the Bose sound system and have an Audi head unit. If that is the case you could try disconnecting the input to the rear speaker amplifier which comes from the Audi head unit. If the cracking disappears then it is something upstream of this rear speaker amplifier. If it remains then it likely that it is being generated in the rear speaker amplifier itself, a dry joint could create this sort of noise. Is the noise there with ignition on but engine not running?

Justin
 
Just looked at a picture of one shown below and it’s not quite as straight forward as I thought as everything connects via a single connector block so not trivial to identify the input pin and pull them from the connector block

8D33D365-E6E1-426F-87DA-D36CFBF0BEAE.jpeg
 
Very much sounds like electrical interference noise to me. I’m a bit of a novice but I believe that when rear speakers are present they a driven off a separate amplifier which is located in the drivers side foot well. I am making the assumption that you don’t have the Bose sound system and have an Audi head unit. If that is the case you could try disconnecting the input to the rear speaker amplifier which comes from the Audi head unit. If the cracking disappears then it is something upstream of this rear speaker amplifier. If it remains then it likely that it is being generated in the rear speaker amplifier itself, a dry joint could create this sort of noise. Is the noise there with ignition on but engine not running?

Justin
One test is not conclusive but no crackling with the ignition on, crackling as soon as the engine started. Will try a few more times.

No Bose, Audi head unit.
 
As the noise is when the radio is off, my guess is that the Bose amp is not going into standby when the radio is off, (it should be put into standby when the switched 12 volts from the radio goes off), so interference is being picked up by the Bose amp. Try unplugging the Bose amp, to see if the noise disappears. This is theory based on the symptom, but I'm not sure where the Bose amp is to unplug it.
Mac.
 
As the noise is when the radio is off, my guess is that the Bose amp is not going into standby when the radio is off, (it should be put into standby when the switched 12 volts from the radio goes off), so interference is being picked up by the Bose amp. Try unplugging the Bose amp, to see if the noise disappears. This is theory based on the symptom, but I'm not sure where the Bose amp is to unplug it.
Mac.
I don't have a Bose system. It is standard Audi but perhaps Audi could have a similar problem?
 
OK, so noise only heard with radio off, ignition on and engine started?

With radio on, ignition on and engine started can you hear this crackling as well as whatever is on the radio?

J
 
I don't have a Bose system. It is standard Audi but perhaps Audi could have a similar problem?
Sorry, miss read, thought it was Bose.
Yes, same theory applies to a non Bose. Rear speakers have their own amp. Again try disconnectung the supply to the rear amp.
Mac
 
Electrical noise, or interferance, does not have the power to drive a speaker. It needs to be amplified to produce the noise on the vid. So, my logic is that the rear amp must have enough power supplied to it, to drive the speaker. I don't think the electrical noise is the problem, it's always there, rather it's a symptom. The problem is how the amp can drive the speaker, when it's supposed to be off (because the radio is off).
Mac.
 
Thanks for your reply's and advice. Little dog has been an unbearable hot dog for the last two days. When he cools down I'll go digging for the amp and report back on what I find. Much appreciated.
 
I’m assuming everything else in that door is working? Could be broken wires where they connect to the plug in the door hinge. I’ve seen it where a couple of wires break and touch each other, could be that the speaker wire is broken and touching a live? Long shot, but very easy to check by pulling the rubber cover/bellows at the door hing back to reveal the wires.

Ian
 
I’m assuming everything else in that door is working? Could be broken wires where they connect to the plug in the door hinge. I’ve seen it where a couple of wires break and touch each other, could be that the speaker wire is broken and touching a live? Long shot, but very easy to check by pulling the rubber cover/bellows at the door hing back to reveal the wires.

Ian
Probably what I will do next, depending on the feedback on today's investigations. Details to follow.
 
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Turn ignition on turn on radio, I get music but nothing from either rear speaker.
I tapped the N/S rear speaker with the back of my hand and it started crackling, engine not running.
I disconnected the amp under the divers floor pan and I still have music at the front and absolutely nothing at the rear. Couldn't get the speaker to crackle.
I suppose I should drive it to be absolutely certain but detaching the amp does appear to stop the speaker crackling.

IMG_0427.jpg
 
It does seem likely there is a fault with this booster amp. I wonder if someone might be able to lend one to try. From what I can see it appears that this amplifier is fed from Block C of the head unit at line level but it does also look like there is a power switch line that turns this amplifier on and off with the stereo. So a cabling issue not completely out of the question. @timmus has posted some articles on converting 2 to 4 speakers so may well be useful to get his thoughts

J
 
It does seem likely there is a fault with this booster amp. I wonder if someone might be able to lend one to try. From what I can see it appears that this amplifier is fed from Block C of the head unit at line level but it does also look like there is a power switch line that turns this amplifier on and off with the stereo. So a cabling issue not completely out of the question. @timmus has posted some articles on converting 2 to 4 speakers so may well be useful to get his thoughts

J
The amp is permanently powered, but is switched in and out of standby via the switched 12 volts from the radio. So there's 12 volts, ground, control (switched 12 volts from radio), left and right line inputs, and the outputs to left (9 &10), and right, (6 & 12), speakers at the amp.
Schematic below.
The pins at the amp, (R12), end are:
2 = +12 Power.
3 = Power Ground
4= Signal Ground
5 = Amp Standby Control (from radio). +12 V = On, 0 V = Off.
9 = Left Rear Line I/P ( LHR Line O/P from radio).
10 = Right Rear Line I/P (RHR Line O/P from radio).
rearspeakeramp.png


Only do the checks below if you are confident with voltage measurements.

So, check for 12 V Power across 3 (-) & 2 (+).
Check for 12 V control across 4 (-) & 5 (+), with radio ON.
If they are all OK, probably the amp.

I strongly suggest you insulate the probes on the multi meter, with sleeving, or tape, so you only have the smallest metal point on the end of both leads. This will greatly reduce the chances of creating a short between pins when checking voltages.

Mac.
 
The amp is permanently powered, but is switched in and out of standby via the switched 12 volts from the radio. So there's 12 volts, ground, control (switched 12 volts from radio), left and right line inputs, and the outputs to left (9 &10), and right, (6 & 12), speakers at the amp.
Schematic below.
The pins at the amp, (R12), end are:
2 = +12 Power.
3 = Power Ground
4= Signal Ground
5 = Amp Standby Control (from radio). +12 V = On, 0 V = Off.
9 = Left Rear Line I/P ( LHR Line O/P from radio).
10 = Right Rear Line I/P (RHR Line O/P from radio).
View attachment 98123

Only do the checks below if you are confident with voltage measurements.

So, check for 12 V Power across 3 (-) & 2 (+).
Check for 12 V control across 4 (-) & 5 (+), with radio ON.
If they are all OK, probably the amp.

I strongly suggest you insulate the probes on the multi meter, with sleeving, or tape, so you only have the smallest metal point on the end of both leads. This will greatly reduce the chances of creating a short between pins when checking voltages.

Mac.
There is 12V across 3 and 2 with the ignition switched on.
With the radio switched terminal 5 gives 12V relative to the space frame. Switch the radio off and there is no voltage at 5. Terminal 4 was difficult to identify due to the number of brown / white wires. There was no PD between 5 and 4 but I suspect I selected the wrong brown / white.
 
There is 12V across 3 and 2 with the ignition switched on.
With the radio switched terminal 5 gives 12V relative to the space frame. Switch the radio off and there is no voltage at 5. Terminal 4 was difficult to identify due to the number of brown / white wires. There was no PD between 5 and 4 but I suspect I selected the wrong brown / white.
Pin 5 to body is fine for measurements, and seems the control signal is fine.
12V, 3 to 2 is good, so power is fine.
I'd expect pin 4 to show as a short circuit (ohms) to body.
You'll not see much on 9 and 10 as they are low voltage signal line out from the radio to the input of the amp.
The 3 wires, pin 5, 9 and 10 go direct to the 20 pin connector on the back of the radio, same wire, so same colour, so, with both ends unplugged, you could continuity check each wire, (ohms), should see short.
If all's well, an amp swap is next move.
Good luck.
Mac.
 
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