This was just recently posted on a soundtraxx discussion I had started about the incompatibilities that could arise when running MTH locos with other DCC equipped locos. I found this 'sounds portion' very interesting,...
>What size sugar cube speaker to install in smokebox?<
My pragmatic response to this query would be “the largest that can be fitted”.
I have now placed a lot of these small speakers (with enclosures) in the smoke boxes of my varied brass locomotives, and each install is different. I do favor the 13x, and 11x sugar cubes if they will fit, but have also gone down to 9x and 8x (both in pairs). They all seem to work well, and sound great- enough different from each other to make it interesting. I use the 3D enclosures from Streamlined Backshop, each of which has enough meat so that one can quite effectively sand, file, or even -with care- a saw to thin and shape the sides to fit.
I have detected no auditory advantage (to my ears, anyway) with dual speakers, except when desired volume with quality sound cannot be obtained in any other way (such as with the small 8x speakers).
Generally, I have firmly moved to never, ever again put speakers in tenders, and I already have removed tender speakers in some in favor of smokebox sugar cubes, or sugar cubes in boiler, fire box, or form fitted under cab roof. What tremendous improvements! The SP cab forwards are an exception, where the the smokebox is separated from the tender by only an apron. Even so, I would bet that two fine sugar cubes alone in the smokebox would do the trick (I have a brass Winton 2-6-6-6 Allegheny with two 13x sugar cubes in the fire box that simply sounds as this gigantic locomotive should sound..
A truly successful recent install was in a KTM LS&MS 4-6-0 (1964). This graceful lank locomotive simply did not have enough room for decoder (Tsu 2 Micro) and speaker of adequate size- without compromising fundamental operating requirements. I installed the decoder in the tender, and a 11x sugar cube facing down in the boiler space above the driveline. The results are spectacular (i.e. spectacular). Tender and locomotive are connected with TCS micro connectors (a six and a two), and wires effectively disguised with a generous application by a black Sharpie pen.
Denny S. Anspach MD
Sacramento CA