Q: We often use an iPhone in some sort of bowl or flower vase as an impromptu speaker for picnics or dinner on the patio. This gives zero stereo separation of course. I understand that the iPhone 4 and newer allow adjustment of volume left and right, so if we had two iPhones to set up as left and right, how can I get the same music to come out of both completely in sync?
A: There are a couple of different ways to accomplish synchronized music playback between two or more iOS devices, but unfortunately they each require the use of third-party apps.
The most straightforward is to use a third-party iOS app called Seedio ($3), which is designed specifically to stream and sync music between multiple iOS devices. In this case, you would install the Seedio app on each of your devices, select the music from your iOS Music library on the first iPhone and setup the second one to receive the stream. Both devices must be on the same Wi-Fi network, however Seedio also supports using the iPhone “Personal Hotspot” feature to create an ad-hoc network if you’re somewhere that a local Wi-Fi network isn’t available.
Note that you only need to purchase a single copy of Seedio for all of your iOS devices that share the same iTunes Store account, however the developer also makes a free version available designed primarily as a receiver so that you friends can install the app to receive music streamed from your device without needing to purchase their own copy. The free version also provides limited broadcasting so that you can try the app out to see if it works for you before purchasing it.
Seedio works quite well as long as your music is already on your device, however it does not support DRM-protected music purchased from the iTunes Store nor does it directly support iTunes Match; in the latter case you’ll have to specifically download any playlists or albums that you want to listen to via the Seedio app.
Another option is to stream music from your iTunes library via Wi-Fi to your iPhone devices using Rogue Amoeba’s Airfoil ($25) combined with the free Airfoil Speakers Touch app running on each of your iPhones. Unfortunately, iOS devices cannot act as AirPlay receivers, and an earlier attempt by Rogue Amoeba to add this capability to Airfoil Speakers Touch met with Apple’s disapproval, so the full Airfoil app must be running on your Mac or Windows PC in order to redirect the audio to your iOS device.
This has the obvious disadvantage of being considerably more expensive unless you already own a copy of Airfoil, but has the advantage of supporting DRM music and an iTunes Match streamed library. In fact, using this method you can play any audio that your computer itself is capable of playing, sending it to multiple iOS devices and even other AirPlay devices.
Keep in mind that the iPhone does not actually allow you to filter left and right volume channels separately—at least not in the native Music app. The option in the Accessibility settings to adjust left/right balance is for adjusting output levels through a connected set of headphones, and does not filter source audio.
Since the iPhone only has a monaural speaker (the holes on the other side are the microphone), this setting has no effect on the audio played through the internal speaker.