Fix: No Volume Control on Multi-Output Device

The Problem

You created a multi-output device in Audio MIDI Setup so you could play audio through multiple speakers at once. It works — audio comes out of all your speakers. But the volume slider in the menu bar is grayed out. The volume keys on your keyboard do nothing. You are stuck at whatever volume level each speaker happens to be set to.

This is not a bug. It is how macOS handles multi-output devices by design.

Why It Happens

When you create a multi-output device in Audio MIDI Setup, macOS combines multiple audio outputs into a single virtual device. The system volume control is designed to talk to one device at a time. Since a multi-output device is actually several devices grouped together, macOS cannot send a single volume command that applies correctly to all of them.

Rather than guessing how to distribute volume across devices, macOS disables the master volume entirely. Audio is sent at full level to every device in the group. If you want to change the volume, you have to adjust each physical speaker individually — walk over to it and press its volume buttons.

This applies to both multi-output devices and aggregate devices created in Audio MIDI Setup. The volume slider will be grayed out, the keyboard volume keys will not respond, and there is no built-in setting to change this behavior.

The Fix: Group Bluetooth Audio

Instead of using Audio MIDI Setup to create your multi-output device manually, use Group Bluetooth Audio. It creates multi-output devices the same way Audio MIDI Setup does, but it adds individual volume control for every device in the group.

The app uses CoreAudio APIs to manage each device's volume independently. This means you get a volume slider for each speaker, plus a master volume that scales all of them proportionally. Your keyboard volume keys work again, and the menu bar volume slider is functional.

How to set it up

1. Download Group Bluetooth Audio from the Mac App Store (free).
2. Open the app. Your connected Bluetooth and wired audio devices appear in the device list.
3. Select the devices you want to play audio through simultaneously.
4. Adjust volume per device using the individual sliders, or use the master volume to control everything at once.

That is it. No Audio MIDI Setup, no grayed-out sliders, no walking over to each speaker to change the volume.

Alternative Workarounds

If you want to stick with Audio MIDI Setup, there are a few workarounds for the volume problem. None are as clean as having per-device sliders, but they work in a pinch.

• Adjust volume on each physical device. Use the volume buttons on each Bluetooth speaker individually. This is tedious but does not require any additional software.
• Use SoundSource ($49). Rogue Amoeba's SoundSource gives you per-app and per-device volume control. It is a powerful audio routing tool, but it costs $49 and is more complex than most people need for this specific problem.
• Use per-app volume tools. Some apps like Background Music (free, open source) let you control volume per application. This does not solve the per-device problem, but it can help if you want to lower the overall output level.
• Control volume in the source app. Many music and video apps have their own volume sliders. You can leave the system volume at full and control playback volume within Spotify, Apple Music, VLC, or whatever you are using.

These workarounds all have trade-offs. Adjusting physical speakers is slow. SoundSource is expensive for a single use case. Per-app volume does not give you per-speaker control. For most people, the simplest solution is an app that handles the multi-output device and volume control together.