Bob C talks about installing speakers to steam smoke boxes to get realistic dimensional chuff sounds.
Most steam locos have a limited amount of space, and sometimes access to the interior of the smoke box is difficult. I used a TDS .623 inch diameter speaker which will fit in most smoke boxes, and has excellent sound for its size.
Size comparison of .623” dia speaker to a dime, and minoval and ¾” speakers.
Brass Steam Locomotives
Brass steam is perhaps the most adaptable to put speakers in the smoke box. Below is a summary of what you can do.
Speaker # 1. The best place on most brass and plastic locos to place the decoder ( a Titan U), and as large a speaker as possible is in the tender.
Speaker # 2. On most brass steam locomotives the smoke box can be opened by pulling the smoke box door out of the boiler tube. In many cases there is a hole in the bottom of the stack into the boiler to let sound escape. My first effort to put a speaker in the smoke box was with a relatively large Pacific with an exceptionally large smoke box. I was able to put a TDS Mini Oval in that smoke box and it fit fine. Since then I have not found a smoke box that large. The new .623 inch diameter speaker fits fine and has excellent sound for its size. Being a round speaker it readily fits into most smoke boxes. The dimensions are1.623″) dia, x 3.5 mm (0.14″) H. With the exclusive enclosure, the dimensions are, 0.7” diameter and 0.5 inches long. If you have room in the smoke box you could add one or two extra enclosure extenders and realize an increase in base and sound quality from the larger baffle volumn.
The smoke box is readily accessed by easily removing, in most cases, the smoke box door. Use a very small, flat screwdriver to place between the smoke box door and smoke box. This usually does the trick. I Wire up the speakers, putting the speaker in the smoke box pointing forward, and try snaking the wires through the boiler to rear of the loco and pulling them out gently with tweezers. If you are not able to do this you will have to remove the boiler/cab shell to get to the wires routed. The next step is to connect the speaker wires to Speaker # 2 wire leads. I usually I leave the larger speaker in the tender as speaker # 1.
In some cases, more so when an Elesco feed water heater is mounted over the smoke box door, the smoke box door is soldered to the boiler. In this case you will have to take the shell off the locomotive and remove or alter the weight if necessary. After the wired speaker/enclosure assembly is together, adhere the back of the speaker enclosure to the front of the weight and place the shell back on the chassis running the speaker wires back to the decoder in the tender.
.623” diameter speaker w/enclosure installed in a Crown Custom Imports HO New Haven I-2 Pacific
There are also some situations where it is not possible to put a speaker in the smoke box. In those situations I have put a mini oval speaker with enclosure in the boiler over the drive shaft. To gain extra clearance I have sanded the enclosure top to fit better against the curved inside of the boiler.
The remaining step is to balance the stereo speakers to have the chuff sound in the stack. I usually leave speaker #2 (in the smoke box) at 100% and speaker # 1 in the tender at 30%. This adds some base sound to the smaller speaker # 2 sound, thus having the sound seem to be coming out of the stack.
Plastic Steam Locomotives
Some plastic steam locomotives are adoptable to putting the .623 speaker in the smoke box. In most cases you may need to remove light sprues and replace with more direct lighting, or remove smoke units to install a speaker. Listed below are some possibilities.
Broadway Limited: Most BLI engines can be modified to fit a speaker in the smoke box, ranging in size from .623 to 1”. Depending on the locomotive, this typically involves removing the boiler weight and removing the front portion of it in order to accommodate the speaker.
Bachmann: Some of Bachmann’s larger steam locos will work with a speaker in the smoke box although you may have to some cutting of the frame.
Athearn: The FEF Challenger and Big Boys will have room in the smoke box if you remove their smoke unit.
Lionel: Larger Lionel steam locomotives can accept a speaker if you remove the smoke unit.
Walthers/LifeLike. Walther’s LifeLike locos are difficult. For all of them you may have to remove light sprues and drill a hole in the base of the stack and the boiler to let the sound out.