Ok, that's odd. According to the 305P Mk II's
owner's manual, its input sensitivity can be set to +4dBu, which corresponds to maximum output at 1.22V input, which is just a shade more power than the Apple dongle is capable of delivering.
I think the +4dBu switch is for pro level balanced inputs with even higher voltage, but the documentation and switch marking is confusing at best.
As best I can tell the gain switch marking (-10dBV / +4dBu) is just for some nominal or reference level and not max level, which is also confusing when trying to match components like this.
The manual also says this.
Maximum Continuous SPL: 94 dB*
Maximum Peak SPL: 108dB*
Maximum Peak Input Level (-10dBV / +4dBu): +6dBV / +20.3dBu
Maximum Peak SPL: 108dB*
Input Sensitivity: (-10dBV input) 92dB / 1m
Which as you said would correspond to (0.316V/1.22V): 1.99V/8V
So I believe the -10dBv is for unbalanced/consumer level inputs and takes 1.99V to get to some max SPL. Peak or RMS input to get to continuous or peak SPL would be too random of a guess for me.
But I also can't square my experience with this input sensitivity spec, whatever that means, which they don't specify. But if it's at 1V, I definitely wasn't getting anywhere near 92dB. I guess it could have been some issue with my phone and Apple Dongle not even getting to 1V? It's a Pixel phone, and with some Google dongle and a generic airport special one I had lying around there was no issue going as loud as I would want.
And there is this in the manual too.
INPUT SENSITIVITY SWITCH – Set this switch to +4dBu to protect from overload when connecting to professional equipment and sources with high output level capabilities. Set this switch to -10dBV when connecting to lower-level consumer-grade audio equipment...
3 Series speakers are equipped with an INPUT SENSITIVITY switch, which is set to the -10dBV setting at the factory. This setting will be best for many applications. However, you should set the switch to the +4dBu setting under the following conditions:
• When connecting 3 Series speakers to professional equipment with +4dBu nominal output level. To determine the nominal output level of the connected equipment, consult the documentation supplied with the connected equipment.
• The sound is distorted, even when the speaker VOLUME controls are set to minimum settings
Issue: The signal is distorted.
• Verify the speaker's INPUT SENSITIVITY switch is set to +4dBu. If the distortion persists, even with the speaker's VOLUME control set low, inspect the gain stages throughout the system to determine which circuit in the signal path is being overdriven. Issue:
The signal level is low.
• Ensure the speaker's VOLUME control is turned up. • Try setting the speaker's INPUT SENSITIVITY switch to -10dBV.
And if I'm interpreting the situation correctly, this is only going to get worse due to volume (voltage) limits which are starting to be applied for hearing protection regulation.
