Distorted audio, internal speakers

[Johnny Calvara]

A few weeks ago the audio on my internal speakers was suddenly distorted. I tried with Boom 2 (equalizer) activated, and I tried without. I used the internet, iTunes and VLC as sources. The device's start-up chime is also distorted. No problem from the headphone jack or Bluetooth. I installed new speakers today, but the problem persists. I did a PRAM reset, coreaudiod reset, and tried logging in as a Guest. I have no peripherals connected to the ports. MacBook Pro 13-inch Early 2011, 2.7GHz Intel Core i7, High Sierra 10.13.6 Thanks

 

[chscag]

That's really strange. I would have done the same as you and replaced the speakers. Since the sound from the headphone jack is okay and BT is okay, we can assume the audio circuitry is working as it should.

Since the boot chime sound comes from the speakers, and that's distorted, it kind of comes back to the speakers somehow being bad.

Did you change out the speakers with exact replacements and made sure everything was wired correctly?

 

[MarkAllread]

Yes, strange!
Do they distort all the way down to zero?
Could be just the drive circuit for the speaker which would be different to the other audio paths. Could be some utility inserted into this path alone...but if you've already logged in as guest then perhaps not. Can you start up with another system disk to see if it still happens?

 

[Johnny Calvara]

That's really strange. I would have done the same as you and replaced the speakers. Since the sound from the headphone jack is okay and BT is okay, we can assume the audio circuitry is working as it should.

Since the boot chime sound comes from the speakers, and that's distorted, it kind of comes back to the speakers somehow being bad.

Did you change out the speakers with exact replacements and made sure everything was wired correctly?

Yes, exact replacements and correct connections.

 

[Johnny Calvara]

Yes, strange!
Do they distort all the way down to zero?
Could be just the drive circuit for the speaker which would be different to the other audio paths. Could be some utility inserted into this path alone...but if you've already logged in as guest then perhaps not. Can you start up with another system disk to see if it still happens?

The distortion is all the way down to zero volume. I will try starting up with another system disk (have to make one). Is that the way to check the drive circuit?
New info: checking with the Boom 2 equaliser, I seem to get most distortion between 200-300 Hz, however, when I use an online frequency generator I am getting no distortion from pure tones in that (or any other) range. With white noise I can’t detect distortion, with pink noise I hear a little, and with brown noise the distortion is pronounced. Streamed audio from the internet (apart from pure tones) still causes distortion.

 

[MarkAllread]

The distortion is all the way down to zero volume. I will try starting up with another system disk (have to make one). Is that the way to check the drive circuit?
New info: checking with the Boom 2 equaliser, I seem to get most distortion between 200-300 Hz, however, when I use an online frequency generator I am getting no distortion from pure tones in that (or any other) range. With white noise I can’t detect distortion, with pink noise I hear a little, and with brown noise the distortion is pronounced. Streamed audio from the internet (apart from pure tones) still causes distortion.

I suggested the alternative startup disk in case there is some software "utility" that is affecting only the speaker path. You could probably do the same by starting in safe mode.
If this doesn't work it could be the speaker amplifier. I don't know the specifics of your Mac circuit, but because speakers usually require more current than headphones, there are extra hardware components in the speaker circuit that might have failed.
You are being very thorough with your trouble-shooting!!!

 

[krs]

A few weeks ago the audio on my internal speakers was suddenly distorted.

Is the sound from both speakers distorted? If so, I doubt the problem is the speaker itself.
I would test each speaker individually, feed a 400Hz, 1 KHz and 10 KHz tone to each one individually to see if both or only one distorts or if both do. That provides a better idea where to look for the problem.
There is probably a source of these tones on the net that you can use and use the balance control to test each speaker individually.

 

[Johnny Calvara]

Is the sound from both speakers distorted? If so, I doubt the problem is the speaker itself.
I would test each speaker individually, feed a 400Hz, 1 KHz and 10 KHz tone to each one individually to see if both or only one distorts or if both do. That provides a better idea where to look for the problem.
There is probably a source of these tones on the net that you can use and use the balance control to test each speaker individually.

Both speakers are distorted. Probably the subwoofer, too, since I get the distortion in the lower frequencies, too.

 

[Johnny Calvara]

I suggested the alternative startup disk in case there is some software "utility" that is affecting only the speaker path. You could probably do the same by starting in safe mode.
If this doesn't work it could be the speaker amplifier. I don't know the specifics of your Mac circuit, but because speakers usually require more current than headphones, there are extra hardware components in the speaker circuit that might have failed.
You are being very thorough with your trouble-shooting!!!

Sorry I didn't get back sooner -- I wrote a reply but couldn't send it because I'm on cellphone internet and it's not been so great lately. I started the computer in safe mode and it made no difference for the sound. I haven't been able to make an external startup disc since my internet hasn't been good enough to download that many GB. If the problem is in the circuitry I doubt I have the know-how nor the equipment to trace and repair it (unless I can find out exactly where to check with a decent multitester). Any suggestions/advice/helpful incantations? Thanks for your support.

 

[krs]

Both speakers are distorted. Probably the subwoofer, too, since I get the distortion in the lower frequencies, too.

There are a number of audio test sites on the net - it would be good if you an access one and run a frequency sweep on each channel separately, both with the speakers and also via the headphone jack.
That would help pin down where the problem is.
Right now I understand the distortion is with all speakers but there is no distortion when using the headphone jack. If you can confirm that via a frequency sweep, that would help losing in on the problem area.

 

[MarkAllread]

...safe mode and it made no difference for the sound. I haven't been able to make an external startup disc since my internet hasn't been good enough to download that many GB. ...

I guess you'll be making a backup from here on ;-)
(don't forget that if you have another Mac, you can use that as a startup disk using firewire if the OS is compatible with yours)

@krs did you see this?

New info: checking with the Boom 2 equaliser, I seem to get most distortion between 200-300 Hz, however, when I use an online frequency generator I am getting no distortion from pure tones in that (or any other) range. With white noise I can’t detect distortion, with pink noise I hear a little, and with brown noise the distortion is pronounced. Streamed audio from the internet (apart from pure tones) still causes distortion.

A pure tone is usually just a sine wave and has no harmonics. They are very clean. You'd probably get distortion using a square wave with the online generator.
Can you recall if the problem started after you had installed Boom 2 or did you just install it to test.
If it was already on your Mac when when the problem started, I would completely uninstall it and all its components.
It does appear that the problem lies in the speaker audio path. It could be a logic board issue and I am woefully ignorant of anything to do with repairing that. But I'm wondering... isn't there a separate subwoofer in the Macbook pro. Could that be the issue?

 

[krs]

No, I didn't see this

when I use an online frequency generator I am getting no distortion from pure tones in that (or any other) range. With white noise I can’t detect distortion, with pink noise I hear a little, and with brown noise the distortion is pronounced. Streamed audio from the internet (apart from pure tones) still causes distortion.

So when you do a sine wave frequency sweep there is no distortion at the low end?
Seems to me, with distortion pronounced using brown noise, that the distortion would be at the low end of the frequency spectrum.
I thought I read somewhere in this thread that there was also a subwoofer in this Mac.
If there is, maybe that's where the problem is.

 

[Johnny Calvara]

There are a number of audio test sites on the net - it would be good if you an access one and run a frequency sweep on each channel separately, both with the speakers and also via the headphone jack.
That would help pin down where the problem is.
Right now I understand the distortion is with all speakers but there is no distortion when using the headphone jack. If you can confirm that via a frequency sweep, that would help losing in on the problem area.

I did as you suggested. I don't get the distortion with a frequency sweep. I continue to get distortion on both channels with music/speech/etc. on all channels but not on Bluetooth or headphones.

 

[Johnny Calvara]

No, I didn't see this

So when you do a sine wave frequency sweep there is no distortion at the low end?
Seems to me, with distortion pronounced using brown noise, that the distortion would be at the low end of the frequency spectrum.
I thought I read somewhere in this thread that there was also a subwoofer in this Mac.
If there is, maybe that's where the problem is.

There is a subwoofer, and it has been replaced with a new subwoofer. There is also distortion outside what should be the frequency range of the subwoofer. Most of the distortion is at the low end of the frequency spectrum, as you said, but it is not limited to that. With a sine wave frequency sweep I don't detect distortion at the low end. I also detect no distortion when I try individual constant low-end frequencies.

 

[Johnny Calvara]

I guess you'll be making a backup from here on ;-)
(don't forget that if you have another Mac, you can use that as a startup disk using firewire if the OS is compatible with yours)

@krs did you see this?


A pure tone is usually just a sine wave and has no harmonics. They are very clean. You'd probably get distortion using a square wave with the online generator.
Can you recall if the problem started after you had installed Boom 2 or did you just install it to test.
If it was already on your Mac when when the problem started, I would completely uninstall it and all its components.
It does appear that the problem lies in the speaker audio path. It could be a logic board issue and I am woefully ignorant of anything to do with repairing that. But I'm wondering... isn't there a separate subwoofer in the Macbook pro. Could that be the issue?

I also thought that a square wave or a sawtooth wave would give me distortion, but I detected none with these waves.
I've had Boom 2 installed for years. Why do you recommend to uninstall it? Just to see if that resolves the issue?
There is a separate subwoofer. I replaced it along with the left and right speakers, thinking my speakers had been blown, but that made absolutely no difference. Waste of time and money (except that I can be relatively sure that the problem does not lie in the speakers).
There is another Mac in the house, but the OS is too advanced for my 10-year-old warhorse.

 

[krs]

I'm out of ideas as far as simple tests and simple fixes are concerned.
From the descriptions so far it seems that there is IM distortion (rather than harmonic distortion), IM distortion is much more noticeable to the ear.
The amount of IM distortion is typically a function of the design of the final amplifier stage. It's possible that some component failed or changed value for IM to raise its ugly head.
I have no clue as to what Apple is using in that regard, if someone had a schematic I could suggest the components to check.
Perhaps look on the net to see if there is some way to check for IM distortion to verify that's what you are hearing.

 

[krs]

I've had Boom 2 installed for years. Why do you recommend to uninstall it? Just to see if that resolves the issue?

I thought you tried it with Boom 2 removed, but now I see you just deactivated it.
I would definitely uninstall it to take it out of the equation completely just to make sure it is not the source of the problem.

 

[Johnny Calvara]

I'm out of ideas as far as simple tests and simple fixes are concerned.
From the descriptions so far it seems that there is IM distortion (rather than harmonic distortion), IM distortion is much more noticeable to the ear.
The amount of IM distortion is typically a function of the design of the final amplifier stage. It's possible that some component failed or changed value for IM to raise its ugly head.
I have no clue as to what Apple is using in that regard, if someone had a schematic I could suggest the components to check.
Perhaps look on the net to see if there is some way to check for IM distortion to verify that's what you are hearing.

Yes, I think we’re going beyond simple fixes here. I’ll start to look into schematics/components/IM distortion. Since I had to pull the logic board in order to replace the speakers, at least I know I can replace it myself if it comes to that ?

 

[Johnny Calvara]

I thought you tried it with Boom 2 removed, but now I see you just deactivated it.
I would definitely uninstall it to take it out of the equation completely just to make sure it is not the source of the problem.

Will do

 

[krs]

Since I had to pull the logic board in order to replace the speakers, at least I know I can replace it myself if it comes to that

Next time you look at the logic board and speakers, see if you can trace the connection from each speaker to a device on the Mac (not necessarily the logic board) and also see if you can trace the connection to the headphone jack. However, if this is a multi-layer board which is likely, that may be difficult if not impossible.
And maybe take some good clear photographs.
I'm trying to determine why you don't get the distortion via the headphone jack and which power IC, if in fact there is one, drives the speakers.