How to play audio on two speakers at once on a Mac

The short answer

macOS can already do this, for free, through Audio MIDI Setup. It is also manual, easy to forget to undo, and quiet about the two things that usually go wrong. Below: that route step by step, the same job in one button, and the part about Bluetooth that nobody mentions until you hear it.

The built-in way, step by step

1. Connect both outputs first, so macOS can see them.
2. Open Audio MIDI Setup (Applications → Utilities).
3. Click + at the bottom left and choose Create Multi-Output Device.
4. Tick both devices. Put the wired or built-in one at the top: the first device becomes the clock master.
5. Tick Drift Correction for the Bluetooth device, and leave it off for the master.
6. Right-click the new device and choose Use This Device For Sound Output.

Undoing it

Switch your output back to the real device in System Settings → Sound, then delete the Multi-Output Device in Audio MIDI Setup with the − button. Skip the second step and it stays in your device list for good, which is why people end up with four of them.

Why it is fiddly

Three things bite. Sample rate: the two devices need a rate they both accept, and nothing warns you when they do not — you get silence or distortion instead. Volume: the keyboard volume keys stop working, because macOS gives an aggregate device no master volume of its own. Cleanup: nothing switches your output back when you are done.

The same thing with Auduo

Auduo is a menu bar app for exactly this job. Pick two outputs, press one button. It chooses a sample rate both devices accept and says so plainly when there is none, turns on drift compensation for the device that needs it, gives you a slider per output plus a master, and puts your previous output back when you press Stop — with nothing left behind in Audio MIDI Setup.

Why two speakers still do not line up

Drift and delay are different problems. Every Bluetooth device adds its own hardware delay, often 100 to 250 ms depending on the codec, and the two rarely match. Drift correction keeps the two outputs from sliding further apart over time; it cannot shift one against the other. Nothing on macOS fixes that without resampling the audio stream, and any app claiming perfect Bluetooth sync is either resampling or guessing. If you need exact alignment, use wired outputs — built-in speakers and a USB DAC land within a few milliseconds of each other.

Common questions

Three or more outputs?

Audio MIDI Setup takes any number. Auduo ships with two slots today; more is what it is working on next.

Does AirPlay work?

Yes. If Core Audio can see the device, both routes can use it — though AirPlay adds its own sizeable delay on top of everything above.

Does any of this record my audio?

No. Both routes ask Core Audio to send the same signal to several devices. The audio itself is never captured, stored or sent anywhere.