Is it possible to install a sound system in an Athearn blue box dummy?
You bet. In fact it would be rather easy compared to a motorized one. Bruce at www.litchfieldstation.com had a photo example on his web site at one time.
Just make sure that the dummy has metal wheels. I have some Athearn dummies that have plastic wheels.
Unless of course you are getting power from a powered loco and running the motor circuit back to that loco. If you want a low price sound decoder with no motor control the Soundtraxx DSX is for you.
Actually one of the best sounding units I have. Dummies in general are better for sound because so much more can be done with the speaker. Not only speaker size but with the baffling/enclosing. Notice the white partitions inside the shell in the picture below. Those seal against the speaker when the shell is on and created a rather large enclosure(for really good lower frequency sounds). The two wires feed to the powered unit where the decoder lives.
If one wants the sound processor/decoder in the dummy unit the wheels must be converted so they can pick up power.
To Texas Zepher: Who makes the BIG one speaker in your photo?
Umm I can’t remember, but it doesn’t matter. Unfortunately last time I tried to get some more they no longer made them. I do still have some sitting about in a box somewhere if you are really interested - they are not cheap.