Selecting Speakers for Large Scale General tips and guidelines: http://www.parts-express.com/pe/showdetl.cfm?partnumber=285-123 small subwoofer: http://www.parts-express.com/tang-band-w3-2088s0f-35-rbm-micro-subwoofer-4-ohm--264-951 http://www.parts-express.com/faitalpro-3fe25-3-professional-full-range-woofer-4-ohm--294-1103 Recommendations for specific locos: I'm making a list here, it's not guaranteed to be perfect, the information is culled from my experience and that of my friends. My recommendations will be for quality over cost, cheap speakers sound, well, cheap! Aristo Dash 9: The stock upward firing oval speaker from Aristo is quite good. It's a 1.5 x 2.5 inch oval. It's fine for most people. There's no enclosure below. The open grill really allows the high frequencies to come out well. It might be worth enclosing the space below to see if you get any more bass, and/or finding an oval speaker with longer "throw". E8: As usual, the stock upward firing oval speaker from Aristo is quite good. It's a 1.5 x 2.5 inch oval. It's fine for most people. There's no enclosure below, but since it's sealed to the roof and no short path "out" sounds pretty good. If you are using a QSI Titan, you can add a second identical speaker further towards the cab, see my E8 page. You can also get replacement speakers in the same size with slightly better sound. I've not tried any larger speakers for more bass, and the fuel tank is best used for additional weight. SD45 U25B: best place is in the fuel tank, no nice vents on top. the fuel tank will hold up to a 3" diameter speaker, but the depth is limited. Get a low profile high performance speaker like the Visaton line.