I was wondering how would a guy go about putting sound in a atlas u30b silver series HO scale that has been converted to a dummy? This loco will always be in a Consist with dcc units..
Just install a decoder that does not need a motor connected to it for the engine to rev.
Install it in the dummy. MRC makes some that can also be controlled with a handheld push botton controller.
Most sound decoders can be used for sound only if you wire a 100 ohm half watt resistor in place of a motor between the motor leads. The 100 ohm half watt resistor is the Soundtraxx Tsunami recommendation, but I don't think that it would be very different if at all with other brands.