My intended layout, Spring Mill Street, won't be much more than a glorified shunting plank so I don't really need small diesels (like this Class 25) to be fitted with dual motors.
Here, I've removed the motor at the no. 1 (radiator) end which leaves just enough room for a 50mm, 8 ohm Visaton speaker (with custom enclosure). The lower stall current requirement of the single motor also means I can use a ESU Loksound V5 L decoder (XL version not required).
I think the single, "large" speaker - pointing-up through the roof fan grille - makes the most of this fantastic sound project created by Ian Bishop (legomanbiffo).