Given that the headphones work with your iPhone, this suggests that the QC15s themselves are fine, so the issue is more likely with the way macOS is handling the impedance or connector type when you plug them in. The QC15 uses a standard 3.5mm TRS plug, but sometimes the Mac’s headphone jack can be picky about seating or dirty contacts. A small bit of debris or oxidation can prevent proper detection.
Give the following a try to see if any can resolve this issue:
- Push the QC15 plug firmly into the iMac’s jack—it should click in fully. If it feels loose, try gently rotating it while inserted to ensure full contact.
- Use a can of compressed air or a wooden toothpick (very carefully) to remove any lint or debris.
- Go to System Settings > Sound > Output and see if “Headphones” appears when the QC15s are connected. If only “Internal Speakers” shows, the iMac isn’t detecting them electrically.
- Try resetting the Mac's Core Audio: Open Terminal and run: sudo killall coreaudiod This restarts the Mac's audio system.
If none of that helps, the QC15 plug may not be making good contact with the Mac’s headphone jack anymore, especially since the earbuds still work. In that case, a low-cost option is to try a 3.5mm extension cable or adapter—sometimes those provide just enough difference in tolerance to restore proper detection.
