Helemt Connection Solution
Pilot DAR
"could not hear or be heard in the certain helicopters mentioned"
Your DC H10-13H headsets have a U174 connector fitted. This is sometimes referred to as the US Nato connector (The one with Silver coloured terminals shown in 'Vital Action's very well presented pictures).
The SW300 uses a U174 socket, so that’s why they work there.
The Hughes 500 & Bell 206 along with dozens of other Airframe Types and installations use the UK NATO connector (The one with the Gold coloured shown in 'Vital Action's pictures). Although they look VERY similar and the U174 connector will fit into the UK NATO socket, the Tels ground terminals do not correctly align and they will not work correctly together. Sometimes you can jiggle the connector around and by luck you get some functionality. You will notice that when you attempt to use this combination that they will not lock together properly.
Solution: Purchase an adapter 'UK NATO' inline Socket to U174 (US NATO) Plug as again shown in Vital Actions picture.
These can be purchased on a next day delivery from Most good UK pilot shops. Headset Services, Adams aviation, Harry Medelssohn all normally carry them as standard off the shelf stock. Prices vary between about £15 to £30. If you really want to get flash Dave Clark also do an adapter.
And for info guys, civi avionics systems are standardised at 600 Ohms impedance. Most headsets provide a standard 600 Ohm speakers as standard unlike you domestic ones you may use on your stereo or computer at home of which is 8 Ohm.