The title sounds insane even to myself, but this is an actual issue.

Few weeks ago we connected a set of Microlab FC330 speakers to a computer replacing the previous speakers.

The user soon complained that the new speakers mute themselves every 10-30 minutes. Upon inspecting the problem, it turned out that the windows system volume gets turned down to 0. It's also not that consistent on timing. It mostly turns down when the user is actively using the computer - we once left it overnight and it was still loud on the next morning. But there are also exceptions where nobody is touching the machine but it still mutes.

My colleague who investigated the problem reported that the windows volume also behaved somewhat bizarre. Seemingly turning up few units above zero it was still silent and only started to sound on some 7 or so units of volume. However, when turning down and up manually again, the sound remains audible at anything above 0.

Initially we assumed it's impossible and the problem just coincided with the speaker swap. We removed Lenovo audio driver wrapper, reinstalled Realtek, tried swapping keyboard, but nothing helped. Then we connected the speakers to another machine and the problem remained there.

After all it appears that the problem is indeed within the speakers. How is this even possible? The speakers are connected via 3.5mm jack, can speakers send any commands and is anyone listening for those commands on the computer side??

We tried the speakers on Lenovo machines having 10EC 0662 audio device. But these were the only things in common - they have different OSes (Win7 and Win10) and different motherboards (chipsets are H81 and Q85).

  • In the previous millennium a friend of mine had 10BASE2 LAN with his neighbor. They were also using two old phones to talk to each other. These phones had electric generators with cranks to call the operator originally, but in their case it just made the other side ring. When my friend was turning the crank too fast, there was enough electromagnetic field to (apparently) induce current in a speaker cable nearby, which made his sound card mute itself. Back then we interpreted this (wrongly?) as a part of some defense reaction built into the sound card, that prevents damage to its electronics. – Kamil Maciorowski Jan 18 '18 at 22:55

The speakers are connected via 3.5mm jack, can speakers send any commands and is anyone listening for those commands on the computer side??

You wouldn't believe it, but yes, it is actually possible.

A normal 3.5mm jack can't do this. They have just 3 channels: left, right, ground.

But there are headphones out there with controls on them. These controls are sent on the 5th channel. If somehow the soundcard sees normal audio as these commands, it could interpret normal audio as "volume down".

The only reason I can think of that would trigger this, is if something hits the cable and as a result the cable moves triggering this effect.

I would therefor start by replacing the 3.5mm audio cable for another one and see if the problem persists.

  • Oh, this might be the case! Is there a way to tell apart the 3 channel and more-channel cables by looking at the jack? – Džuris Jan 18 '18 at 22:47
  • Nevermind, we found it ourselves. Just look at the separators and count the conductive sections. The cables are called TRS, TRRS, TRRRS etc where each letter represents a section (T - tip, R - ring, S - sleeve). – Džuris Jan 18 '18 at 22:55
  • Yes. And if a cable can't go all the way in, it may breach 2 sections which is often the case for weird glitches such as mono audio, phased audio, or even worse, sudden weird things like volume down. – LPChip Jan 19 '18 at 7:35
  • Unfourtunately, the problem remains after cable replacement. Maybe you've got any other ideas? – Džuris Jan 20 '18 at 22:32
  • Watch how the cable is inside the slot. If there are metal bars from the case preventing an exact insert into the computer, it may be the cause of this. Usually these cables have plastic connectors that you can cut into with a knife to solve this issue. – LPChip Jan 20 '18 at 23:21

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