I am seeing the following behavior on a MacBook Air and an iMac.

We have external speakers set up that we connect to via USB > external sound card > speakers. When we initially connect, the audio works as per normal, sounds great. Then after about a minute it mutes completely, and won't turn on unless we reconnect the usb and select it again as the output. It's not iTunes or Spotify because using the volume up and down keys does not make any sound either.

The iMac started doing this 4 or 5 months ago and now it has just started on the MacBook Air. This also happens on the MacBook Air when I try to connect audio out to the external display I have connected to it, so I don't think its the sound card, I think it might be OS software related.

Sound panel screenshot: Sound panel screenshot


Some more info - when I switch between the two USB audio outputs in the sound panel, I get a short flicker of sound before it cuts out again.

Another edit:

Turning off Bluetooth and WiFi had no effect - the problem still persists

  • so what does it say in the sound pannel
    – Ruskes
    Commented Feb 28, 2014 at 13:48
  • everything is normal in the sound panel, I can see the external speakers, and they're still selected
    – koosa
    Commented Feb 28, 2014 at 13:50
  • who/what else is in the sound pennel
    – Ruskes
    Commented Feb 28, 2014 at 14:01
  • I just added a screenshot
    – koosa
    Commented Feb 28, 2014 at 14:08
  • also just added some more info...
    – koosa
    Commented Feb 28, 2014 at 14:12

1 Answer 1


I have problems with the Alesis M1Active 520USB speakers. After an undetermined amount of time they just stop working. Switching to internal speakers works fine. A reboot fixes it...but that's painful. The easier solution I've found is this:

  • Change your sound source (option clicking the sound icon is the quickest method) to Internal Speakers.
  • Unplug the speakers
  • Open a terminal and run this command, which restarts the Core Audio Daemon: sudo killall coreaudiod
  • Plug the speakers back in

Maybe it will help you too.

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