Lou, acoustic suspension speakers are sealed enclosures much like the small plastic cans most people use in toy trains. They are never as efficient as vented cabinets such as base reflex or transmission line enclosures. With this puny amp one really needs a vented design. I have not tried to build a BR or TL enclosure to fit inside a locomotive though I think one could fit inside an unpowered unit. What I do is mount the speaker at the top of a cardboard or plastic tube with the back of the speaker frame against the tube, speaker cone facing UP. I open the speaker holes in the floor of the loco as much as possible even to the point of cutting them entirely out. One thing not to do if you need more volume is to mount the cone 4-5mm from the tiny holes in the floor of the loco. It's OK to mount it on the floor if you are willing to cut a hole the size of the speaker cone. You must let the cone breath to reach it's full excursion. Even if you are unwilling to cut the hole in the floor of the loco the speaker mounted at the top of the tube giving a 1.5-2" air space between the cone and the sound holes in the floor will add noticeable volume. When Lionel came out with RailSounds 1 in 1989 they used an amp that was far too weak and my quest for more volume prompted me to try dozens of ideas to get more volume and the speaker facing up at the top of a cardboard tube was noticeably louder than any fully closed enclosure I tried. Sealing the body and any small holes in the floor of your loco may help a bit but not to any great extent that I can tell just by listening. Most who have heard my modified locos find the volume much too loud including myself so I turn most of them down a bit.
Fully sealed speakers in music and home theater setups became popular when high powered amps became cheaper than shipping large speaker cabinets to the store. The smaller the enclosure the more power you need as well as more equalization (tone control) which again ups the power requirements. A friend of mine has the greatest sub woofers anyone has ever heard, not to mention the rest of his system . Two cabnets approximately two foot square each cabinet with two 16" woofers back to back facing out in a dipole fashion. He is driving each cabinet with a 500 watt amp on each one. He wanted to build the cabinets with twice the interior volume as it would cut the power requirements by 75% for a given sound pressure level. However his wife would not stand for the larger cabinets so he bought the big amps instead. A sealed speaker cabinet is NOT an echo chamber but rather a spring that the speaker cone reacts against. The smaller the cabinet the stronger the spring and the more power it takes to drive the cone to full excursion against the spring. Your going to need vented enclosures or much larger enclosures with the small ERR amp. j
