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Engine Whining Noise


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#1 Sam Biscuits

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Posted 12 September 2019 - 04:48 PM

Hi guys, I've just installed speakers on my parcel shelf, but for some reason I get a whining noise on them when the engine is on. The pitch of the sound changes depending on the revs of the car and my other speakers in the car are don't have this problem. Anyone got any ideas?



#2 unburntfuelinthemorning

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Posted 12 September 2019 - 04:59 PM

Are the speaker wires close to the main battery cable?



#3 Sam Biscuits

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Posted 12 September 2019 - 05:13 PM

Actually I've just checked, it is on all speakers (2 x parcel shelf, 2 x under the rear seats and 2 x speakers on the dash). The front speakers are on a different output on the head unit to the other 4. The sound is on the speakers as soon as I turn the engine on (no music playing).

 

I've moved the speaker wires as far as I can away from the main battery cable, though some are fairly close. The from speakers wires however are nowhere near the main battery cable but still have the sound on them.



#4 unburntfuelinthemorning

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Posted 12 September 2019 - 06:00 PM

Are you sure it's alternator whine and not ignition noise?

 

Is the interference with the radio only or with other media too?



#5 Sam Biscuits

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Posted 12 September 2019 - 06:21 PM

Alternator whine does make more sense.

 

Just had a play with the system, I ran two pairs of phono cables from the head unit in to the amp in the boot. To do this I snipped them to feed through tight holes and then soldered them back together. When I remove the phono plugs from the amps, the whining stops. Maybe it's because where the solder joints are there is no cable screening?



#6 unburntfuelinthemorning

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Posted 12 September 2019 - 08:43 PM

Could be.  So when did the noise start?  When you added the rear speakers and an amp?


Edited by unburntfuelinthemorning, 13 September 2019 - 01:07 PM.


#7 Sam Biscuits

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Posted 12 September 2019 - 09:57 PM

Been thinking about this. I've done the build in stages and I think it started when I ran the first pair of RCA cables using a different amp. Now have a much better amp, but have ran another pair of RCA's. I have ordered more cables and will install without cutting and soldering. Fairly confident this is this issue. Before I ran the RCA's I used the same parcel shelf speakers but had no issues. Hopefully this'll fix the problem.



#8 unburntfuelinthemorning

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Posted 13 September 2019 - 01:08 PM

I'll be interested to know if your new cables solve the problem.



#9 Sam Biscuits

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Posted 13 September 2019 - 06:58 PM

The RCA cables didn't fix it. Confirmed it's definitely the Alternator I'm hearing on the speakers. Checked the grounding on the Alternator and the head unit, but need to do a proper job of the head unit as I'm not convinced.

 

I've got the pair on the parcel shelf sharing pos and neg on the same amp channel, similarly with the speakers under the seats. Would wiring them in series (only having a single wire on the pos and neg per channel help here? All the speakers are the same impedance.



#10 MikeRotherham

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Posted 14 September 2019 - 05:48 AM

Is this thread any use?

 

http://www.theminifo...ternator-whine/

 

The image shows a suppressor fitted to the ignnition coil which is not applicable here but posts 8 and 9 seem relevant.


Edited by MikeRotherham, 14 September 2019 - 05:53 AM.


#11 unburntfuelinthemorning

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Posted 14 September 2019 - 06:54 AM

I've got the pair on the parcel shelf sharing pos and neg on the same amp channel, similarly with the speakers under the seats. Would wiring them in series (only having a single wire on the pos and neg per channel help here? All the speakers are the same impedance.

So you're powering the parcel shelf speakers with a single channel amp?  Or you're using a two channel amp with one channel powering the parcel shelf speakers and one channel powering the under seat speakers?

 

What is the minimum impedance your amp can cope with?

 

What is the impedance of the speakers?



#12 Sam Biscuits

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Posted 14 September 2019 - 09:41 AM

I'm using a 4-channel amp for 6 speakers, a pair in the front, pair under the seats and a pair on the parcel shelf. All the speakers are 4 ohm, not sure on the minimum impedance of the amp. At the moment I have both under the seat speakers on a single channel in parallel, both parcel shelf speakers on a single channel in parallel, and the two front speakers are on their own separate channels.



#13 unburntfuelinthemorning

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Posted 14 September 2019 - 10:00 AM

Your 4 ohm speakers connected in parallel at the rear means the amp sees a 2 ohm load on those channels which it may not be designed to cope with.  That isn't good for the amp and it may be a factor with the noise you're getting.  Try having one speaker on each of the rear channels just to see if that makes any difference to the noise.  It'd be worth checking those amp specs too. 



#14 Sam Biscuits

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Posted 14 September 2019 - 06:36 PM

Reworked the speakers and replaced the RCA’s with decent ones. Also fitted a noise suppression filter in to the head unit power input, but still have the alternator whine!!!

Got some filters for the RCA’s on the way so fingers crossed that sorts the issue out.

#15 viz139

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Posted 14 September 2019 - 07:00 PM

You changed the amp and cables but the problem still there so I would be looking at the headunit  or altenator.  If you could borrow an altenator it would quickly rule out a faulty regulator. Using an adapter you can connect the RCAs to music on your phone and with the engine running check the amp without the head unit. How high have you set your gain levels?






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