I like to add sound effects to model structures and selected pieces of rolling stock. Little things like noisy sheep and cattle in stock cars, gambling railroad workers in a caboose, or industrial sounds in buildings help bring a model railroad to life. ITT Products has a fairly extensive line of HQ sound modules that are easy to use. These are 1.4" x 2.3" x 0.4" circuit boards that consist of a voltage regulator, a sound chip, audio amplifier, volume control, and terminal strips. These modules have a maximum play time of 60 seconds depending on the scenario programmed into them, and can be played one time, or continuously looped until turned off. Just add a battery, switch and speaker and you are set to go.
I like to use as large a speaker as possible. I have had extremely good luck with this particular oval speaker. It is available from Jameco, P/N 2115442, and is only $2.49 for a pair. Each speaker is 1.6” x 2.8” x 0.9”. They are rated at 3W, 8 ohms, 82dB output SPL, and 310-12000 Hz frequency response. The speakers come pre-wired to a 4-pin connector, probably for some type of stereo application. I remove the factory wiring and install my own wires and connectors. http://www.jameco.com/
When I use a speaker inside of a structure, I generally build an enclosure to disguise it and to direct the sound downward towards the floor. I start by making a small open box to represent a table, workbench, or cabinet. This enclosure is made from 2” x 8” boards with 4” x 4” legs. I made the inside dimensions slightly larger than the speaker frame so that the metal frame does not touch the wood. I added wire leads and a 2-pin connector so that the speaker can be easily replaced if needed. I attached the speaker inside of the enclosure with double-stick tape.
I added a few 1” x 6” boards, hinges and handles to the front of this enclosure to make it appear like a storage cabinet. After a few detail parts are added to the top, it will be ready to go into the repair shed I am building. I will attach it to the floor with small beads of silicone to dampen the vibrations and keep the window panes from rattling.
Bob Hyman