Very strange issue with left speaker (21,5" mid 2011)

[saronno]

I have a very strange issue with the left speaker of my imac 21,5 mid 2001:
the left speaker works but the sound is low and sometimes lack of boost.

Anyway, if I reset PRAM everything works fine but, after a while, the problem come back again.

I also give a check to the connection internally and they are fine.

At the moment I have high sierra installed. Anyway I don't think it's a OS issue since, even the
starting sound is affected when the problem kick in.
It's probably something having to do with EFI / PRAM.

Any idea?

 

[mikehalloran]

If it goes away after resetting the NV RAM but then comes back on startup, the obvious first step is to replace the NV RAM battery. This may not be the problem but it’s the first step.

If it still has a HDD, use a BR2032. If an SSD, you’re good with a common CR2032. The only difference is the higher heat resistance of the BR2032.

To replace it on a 2011, the screen has to be loosened and moved towards the top so tha the lower lip clears the groove. Now the bottom can be lifted to give easy access to the battery.

Now that you’ve done most of the work, it’s the perfect opportunity to replace that 7 year old spinner with an SSD.

 

[saronno]

I tested it yesterday and it showed 2,95V ... it doesn't seem so low to cause an issue.
Anyway an SSD is installed.

What about a software issue?

I made another test an hour ago: I restart after one hour the mac, issue came back, then I restarted with "restart" from menu ... issue disappear again. Since it works well when you reset anything, I would exclude some problem with the speaker. If speaker was faulty, nothing could make it works well again.

Another thing I wonder is ... if the mac is connected all the time to power, battery shouldn't be an issue because usually the battery keep nvram information whn you disconnect the mac from power. Am I wrong?

 

[saronno]

Mmmmm ..... I try to unload and reload "AppleHDA.kext" and this solve the problem right away without restarting the mac.

It seems clearly a software issue to me.

sudo kextunload /System/Library/Extensions/AppleHDA.kext
sudo kextload /System/Library/Extensions/AppleHDA.kext

Something is messing up the audio. It happens sometimes from the beginnig (cold start),
it happens when you wake up the mac from sleep and it can be solve reloading kernel audio module ....

 

[saronno]

https://www.ifixit.com/Answers/View/395243/Left+Speaker+pops+&+looses+its+bass-mid+frequencies

It's exactly the same problem I have. As I said previously, you can reverse the issue reloading the audio service,
but I can't find a definitive solution.