Speaker off while headsets on.
I hesitate to write this as I expect a flood of heated responses but here goes.For many years an argument has carried on among Airbus pilots concerning the use of the cockpit loudspeaker volume knob.There are two basic positions. 1. It must be on loud enough to hear the radio transmissions always unless there is a specific reason to turn it off or down such as he is listening to HF. 2. It can be turned right down or off when headsets are used.Argument 1 is claimed to be backed up by the SOP but the SOP does not state that it must be set to the 1 o’clock position AND LEFT THERE FOR THE WHOLE FLIGHT.Argument 2 is claimed to be backed up by the MEL which implies that only 1 level of redundancy is required but this is hardly iron clad.I fully understand the argument in favour of leaving it on, but I personally have over many years experienced a problem when I am using headsets and the other pilot has his speaker on, in this situation there seems to be an interference between the sound coming from my headset and the sound coming from his speaker. I theorise that this may be due to wave interference but whatever the cause I know it is a problem for me. It causes me to miss calls and that is not good.I was wondering if there is any official literature on this subject.