I just finished an install of a Tsunami TSU-750 "Galloping goose" in my Bachmann 0-4-0 siderod. The speaker I ordered with it is small .40 (10 mm). I also used the Soundtraxx enclosure for it. I did solder the "Keep alive" capacitor to the decoder. The decoder is in the cab, the capacitor in the engine compartment. I tried to fit them both in the engine compartment but just not enough space, so right now the decoder is on the left side of the cab. The speaker/enclosure I mounted on the roof of the cab. The sound isn't the greatest. You can hear it but with two steam locos on the layout running they tend to drown out the siderod. While I had it apart I glued an engineer on the seat. I just need to do something with the decoder in the cab and then figure out what I'm going to do with the speaker on the roof. I drilled a small hole for the wires to fit through and I drilled a hole in the roof approx the size of the speaker. It runs great, just doesn't have the sound I would have liked.