Use of personal earphones on Flight Deck

[Mister Geezer]

Hi all

I fly a Boeing and in the cruise I have occasionally taken my own personal set of Sennheiser earphones and plugged them into the headset jack for ATC comms, with the help of a 3.5mm to 6.5mm adaptor.

The quality of the audio is excellent and it helps avoid having the speaker on too loud which in itself can be a source of harmful sound on ones hearing. The only problem is that I can only get audio in one ear.

Any ideas as to how one can get audio in both ears with the above situation?

Thanks