Mago is correct, the iPhone volume control via their volume buttons is for streaming volume only. In fact, it’s the ONLY option I know of for iPhone streaming volume control.
For mic (on the OPN volume), either use the manual buttons on the OPN (which is still my preferred method because I don’t even have to reach for the iPhone every time), or use the MFI Hearing Devices sliders (which you can quickly access by 3 quick clicks on the Home button), or via the ON app (which you will have to open and wait for the OPN to establish connection to the app).
I would only use the MFI Hearing Device slider if I already have my iPhone in hand doing something else. Then I can just triple click on the Home button and I’m there already. Don’t need to reach up to my OPN manual buttons.
I would never bother with the ON app for mic volume control because like I said, you’d already have the phone in hand, wake the phone up, login to the phone, turn on the ON app, wait for the OPNs to connect on both sides, before you can touch the mic volume control. Way too much trouble. I hardly ever touch the ON app at all ever unless I want to see what firmware version my OPNs are on.
If you’re in TV Adaptor mode, then you can control the TV streaming volume in a few ways. I normally just change the volume of my TV if its output is a variable volume input into the TV Adapter. But if you turn it down too low, the TV Adapter would go into standby if not detecting the threshold volume level after a few minutes. So if the threshold volume level from the TV has to be high enough to keep the TV Adapter from going into standby and you find that this level is too loud for your OPN, then I’d use the manual button on the left OPN to turn it down to my liking. That would also turn down the mic volume however.
To avoid turning down the mic volume in conjunction with the TV Adapter volume, I would use the MFI Hearing Device TV Box slider (which is separate from the Mic slider). This way, the Mic will be at normal volume so you can hear surrounding sounds while listening comfortably to the TV.
One thing worthy to note is that in the TV Adapter mode, if you adjust the Mic volume (either via the manual buttons or via the MFI HD Mic slider), it has an effect both on the Mic volume and the TV Box volume. You’d think that Oticon should keep the TV Box volume independent from the Mic slider/manual buttons, but I don’t know why they chose to tie them together.
On the other hand, if you’re in the iPhone streaming mode, the Mic slider control and the iPhone volume control are not tied together, which is how it should be for both this mode or the TV Box mode. So let’s say if you’re in a noisy car and want to block out the external mic noise completely, turn down the Mic slider or manual OPN button to zero, and you’ll be able to hear only the iPhone streaming volume. You can then adjust the iPhone streaming volume to the level you like.
