The G class was V/Line's largest diesel loco - the model should therefore be capable of handling a very large speaker. A 20x40 mm speaker with enclosure would have packaged very nicely in the model and presented the best sound solution, had it been planned for. It is what it is, and instead we have space for two 23 mm speakers, but not an enclosure as the PCB gets in the way. No enclosure = very tinny, poor sound. Instead, there is space for an ESU 16x25 mm speaker and enclosure at the end of the PCB, just.
Disassembly requires removal of couplers and four body mounting screws, which itself requires removal of the brake cylinders (!) and then be prepared for the brake lines to also come off. Put these small parts in a safe place. Plug the decoder's 8-pin plug into the 8-pin socket (Pin 1 = orange) and mount the speaker such that it is facing up in its enclosure. If the speaker faces down it will contact the top of the drive tower. The white speaker enclosure can be affixed to the chassis. Refit body and bogie brake cylinders previously removed, including couplers.