My 16x35mm speaker were too deep (~8mm), when placed in the factory speaker mount, the fuel tank would not fit back on the chassis. So I used thinner (~5mm) 20x35mm & 20x40mm speakers without the factory mount.
Soundtraxx Tsunami in 2-8-8-2.
Digitrax DN144K installed in a 44 tonner, motors wired in series.
Digitrax DZ-121 installed in a 44 tonner, motor wired in series.
Lenz LE103XF installed in a H16-44.
Digitrax DZ121 installed in 4-8-2, I removed the four pin connector between the loco and tender but kept the two pin connector for power pickup. I reused the two internal two pin connectors, one to bring track power from the square PCB to the decoder (on left in pic), the other to run from the decoder to the firebox light (on right in pic). I moved the wires from the firebox light to the pads of the removed four pin connector and a couple of jumper wires to connect the track power to the other connector.
Soundtraxx DSX installed in the tender of Bachmann GS4 4-8-4.
Also with Digitraxx DZ-143 in the loco with firebox flicker LEDs and headlight and Gyralight.
Soundtraxx TSU-0750 light logging with 27mm high bass speaker, factory PCB removed.
TCS M1 in 0-6-0. Decoder fit up into the smoke box.