I have a sd40-2 with dcc it has the holes for a speaker in the fuel tank. Is it possible to add sound to this engine?
For the SD40-2 Soundtraxx offers two decoders and a speaker/baffle kit:
Full Tsumnami2 decoder: TSU-PNP8 (PN: 88513)
Cheaper Econmi decoder: ECO-PNP (PN: 882004)
Speaker/Baffle kit: PN: 810113
Sound decoders and speakers from other mfg's may also work.
Len
DCC Sound Decoder Install on a Bachmann SD40-2 Diesel locomotive, See link below.
https://www.bachmanntrains.com/home-usa/board/index.php/topic,38200.0.html
DR, the OP says his loco already has speaker holes in the fuel tank, so there's no need for him to order a replacment chassis as shown in the link you give. And the TSU-BH1 decoder shown should be a 'drop in' replacement for the 'SoundValue' decoder board, without a lot of modification, if that's what he has.
Len
It's possible to put sound in anything. What varies is the amount of work required.
Much older models that were produced before sound became an every day feature often used up all the possible space inside the locomotive shell for weights to enhance tractive effort. If you get one of those, you have to remove a lot of weight to fit in the sound equipment, but then you reduce the Hauling capacity of the engine.
A lot of the time in such cases, you are better off just buying a new engine that has sound in it already. Not only is the installation work done for you, but other technologies in the engine such as motor quality and gearing are often much improved over older models.
If you are asking if such installation work is possible, the required work is quite possibly beyond your ability if you are a beginner. They are many professional techs who will do the install for you, but their labor plus the parts can run well up over a couple of hundred dollars, and that considerable number might make more sense to just buy a new engine that has sound already.