Minelab Sdc2300 Audio Adapter plug 

Cheapest on ebay with postage included in price

Audio adapter plugs into sdc2300 audio socket allow you plug in a speaker or your preferred headphones it has a 1/4 jack (6.5mm) so you no longer need to use supplied headphones

multiple quanties available

it can also used with a 3.5mm adapter plug  (Not Included) purchased from jaycar bunnings etc under $5


also have this listed with a sdc battery upgrade bundle
local pickup from colac victoria is also welcome