The 2nd production run chassis has had a minor design modification done whereby mounting is now provided for a speaker at the #2 end only.
Compared with the 1st production run, the ESU LokSound V5 21-MTC (58429) decoder is now mounted upside down in the model. In the example below a DCCSound Premium speaker is fitted, featuring twin 13x18 mm sugarcube drivers. The sound enclosure volume is 3.5 times greater than that of the original speaker.
It's a simple plug-n-play solution for sound. Splay the shell sides out and remove the body. Replace the DC jumper board with an ESU 54499 21-MTC decoder and place the 20x40mm speaker in the enclosure. Seal around the perimeter of the speaker and any gaps around the sound enclosure with Krystal Klear or similar for a much better result in sound quality.