Why not just put sound into the A unit? Some DCC systems, NCE for example, automatically have things like the horn and bell be operated from the lead unit, which for you would be the A. I would find it disconcerting to operate the horn and have the sound come from one unit back.
Are the decoders in there now have the 8 pin connecter? Digitrax has 16bit decoders: SDXN136PS with the 8 pin connecter or SDXH166D hard wire style although you can get an 8 pin adapter for this. You should be able to put in a 1" speaker in the b unit. Soundtraxx has the new Eco namai decoder as well. Like sugested, give both units the same address. Joe
If they are going to be always conencted, just give them the same address. The cound decoder will respond to the sound functions, and the motor only decoder will do nothing, or maybe turn on some function outputs that have nothing connected, which does nothing and causes no problems.
Multiple decoders in one loco can be troublesome. It would be best to replace the motor decoder in the B unit with a single decoder that does sound and motor.
--Randy
Modeling the Reading Railroad in the 1950's
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I have a pair of F7 units, A + B from Bachmann with simple Digitrax decoders. I am considering adding sound to the B unit only. Since these two are consisted virtually all the time, sound in only one seems fitting. I am trying to make sure that with the A unit as the lead loco I will be able to control sound in the consist. Some feedback on how to make sure this happens would be welcome, as well as some suggestions as to the best choice of decoder to get to keep cost low but not limit function too much. Don't know if I should replace the entire decoder or add simple sound decoder. The current decoders were added by the seller to a DCC ready engine when purchased.