Ever want to watch a movie together with a friend and keep the audio private between the two of you? In the old days, you might have used a headphone splitter with two inputs for your Mac’s one headphone port.

If your headphones were wireless, you probably thought you were out of luck. In fact, for quite some time it’s been possible to connect multiple Bluetooth headphones and play to all of them simultaneously.

Enter Audio MIDI Setup

MIDI (Musical Instrument Digital Interface) has been around since the 1980s, including on Apple computers, as a means to connect electronic instruments, computers, and devices that play, edit, and/or record music. Routing audio among multiple devices is in its DNA, so to speak.

If this is all Greek to you, it’s no wonder the Audio MIDI Setup utility has been available on Macs for over 20 years with little engagement from users. One of the features of this application, which you can find in your Utilities folder, is to aggregate multiple audio devices and play sound through them at all once.

Connect Multiple Devices

The first step is to connect the headphones you want to aggregate. According to the official Bluetooth specifications, a Mac supports up to seven simultaneously connected Bluetooth devices. Practically, though, more than three or four may produce too much interference for an acceptable experience.

If you are connecting headphones that have never been paired with your Mac before, follow the instructions to put each device in pairing mode and use the Bluetooth settings panel on your Mac to connect.

Some headphones can only store one host device profile and must be unpaired or reset before they will pair anew. Others can store more than one profile and may even be able to alternate between active devices with ease.

Build a Multi-Output Device

In Audio MIDI Setup, click the + and choose Create Multi-Output Device. On the right, check the headphones you want to include in the device.

If one of the headphones is physically connected with an audio or USB cable, make it the Master Device. If none, pick the higher quality device.

Then, enable Drift Correction on any other devices. Since there can be a slight delay in Bluetooth headphones producing sound, this attempts to keep the audio feed in sync so everyone hears the same thing at the same time.

If you wish, you can also give your Multi-Output Device a different name. Just click twice on it and type the new name.

Select Your New Device

Finally, select your new output device as the sound source. You can do this in the Sound menu, which looks like a speaker or headphone, or in the Sound section of Control Center, as demonstrated above.

I’ve found this feature especially handy on airplanes where managing multiple devices is already challenging. And I tend not to fly on planes with individual entertainment systems — where one of Twelve South’s AirFly products would come in handy.