installing tsunami sound decoder in a sd70mac athearn gen. - Model Railroader Magazine

Scott,

I've done a couple of these and used 2 speakers.   

1. I milled out the tank with my dremel enough for a 1.1" round speaker.  Made a mesh cover to keep the speaker magnet from picking up junk off the track and getting into the speaker.    I used adhesive putty to provide sealing as an enclosure using the tank and removable sides.

2. Since I have one speaker pointing down, the radiator speaker points up.   For this I used a medium speaker with large magnet.  There are 2 primary  "medium" oval speakers on the market, I used the larger one from DCC Installs&Sales.     I cut off the side pieces of the enclosure for that speaker and filed the sides of the speaker itself.    This is the only way to get a large medium speaker in the shell.  I used the locomotive sides as part of the enclosure and also had to file a little inside the shell.  I used adhesive putty when installing this to go around various holes.     I've also found that making an enclosure out of thick cardstock, maximizing the size provides good sound vs the smaller plastic enclosure.   Thick cardstock seems to help the bass vs plastic stock--but maybe that's just me.

You can wire the speakers in parallel or series, whichever you prefer.  

Richard