Looking for a sound decoder?
No matter what scale you model there are several factors to consider when deciding which sound decoder to purchase. First you need to see if anyone actually makes a decoder that will fit, especially if you model in Z or N scale. With the introduction of sugar cube speakers there are more models in which sound installation may be possible. The main limitation really is a matter of whether there is a decoder that will fit. While sound decoders will fit in many N scale steam locomotive tenders, many diesels remain a challenge. Streamlined Backshop (www.sbs4dcc.com) has a fairly comprehensive list of decoders for various scales.
There is a much wider selection of sound decoders available for HO scale and larger models, and installation is generally easier. Many manufacturers offer plug and play versions of their decoders that may only require plugging in the decoder, installing a speaker, and hitting the tracks. TCS offers kits containing their WOWSound decoder, a motherboard, speaker, and speaker enclosure designed for specific locomotive models. These are a great option for anyone who has never installed a sound decoder and practically guarantee a perfect fit.
At one time stall currents were a concern when selecting a decoder. However most models made today have very efficient motors that draw under 1/2 amp and most decoders now can safely provide 1 amp operating current. If you have older motors made before about the year 2000 it is a good idea to see how much current it draws. As a guide open frame motors generally draw more current than can motors.
The final concern is whether or not the available decoders actually offer the sounds package you need for a given locomotive. On their website Soundtraxx has a great page listing many of the types of steam and diesel locomotives and the proper sound package for them. There is a listing of the various prime movers used in diesel locomotives and an excellent one on the types of horns many railroads used. Digitrax, Loksound, Soundtraxx, and TCS all have pages on their websites where you can listen to clips of the sound packages they offer. So finding the right decoder is mainly a matter of doing a little research.