N Scale, which I model, has been getting better with sound, a lot better. But there are still excellent locomotives like Kato SD-70s and many other well manufactured diesel locomotives that just don’t have the room to install a good speaker, no matter how good the decoder, to get reasonable sound produced. I tried the MRC drop-in decoder and speaker, but it just did not have any volume. In fact, after sending an email to MRC about the lack of volume, I actually received a response back from them that they realized their sound was only audible inside of 2 feet. Why have it if that is all you can hear.

This may not be the answer for everyone, but making a “sound box car” has really brought me to a new level of satisfaction in N Scale sound. I used a Micro Trains 50’ Express refer for my project. Additional parts (with approximate costs) were:
Digitrax SDN144PS Sound Decoder $ 39.10 (Litchfield Station)
14 x 25 mm 8 ohm speaker $ 5.89 “
1000 uf 16V capacitor $ 1.59 “
100 ohm ½ watt resistor $ .15 “
Richmond Controls axle wipes & bolts $ 3.82 “
Richmond Controls connectors $ 1.00 “
Micro Trains 50” refer $ 16.00 ( e-Bay )
Total $ 67.55

I used the wiring diagram from Streamlined Backshop Services ( Streamlined Backshop Services Sound Car Kit_Instructions.pdf ) and followed their recommendations on the CV settings on the decoder since I did use the resistor. I did not drill all the holes they show in the car base, but instead built a speaker enclosure out of styrene and mounted the speaker facing upward. In using the refer, I found that in opening the roof hatches, the sound volume was greatly increased. So I glued the doors open, otherwise I was going to loose them for sure.

The basic sound on the decoder was ok but I found that in downloading the Digitrax sound file for the SD70, I had really good sound. In fact, I may end up turning the volume down a bit, especially when I use it on my home layout. But when my club goes to a show, and we take our N-Trak layout, which is over 20’ long, people won’t be guessing on whether they can hear sound…..they will.

Another nice advantage in using the Digitrax decoder, by installing the resistor, you can program different ID’s. So I can take the sound car, program a loco number that I want to use it with, and off I go. If I want to run it with a different locomotive the next day, just reprogram the number, and you are ready to run. Also, in using the refer, it doesn’t look out of place immediately behind the locomotive.

Following are three pictures:
Top view showing the parts and speaker facing upward.


Side view - the connectors made life easy.


Bottom view, showing the axle wipes. The Richmond Controls axle wipes seemed to let the trucks rotate much easier than the wipes that rub directly against the wheels.


My plans are to make four sound cars which should give me lots of flexibility, especially since I can reprogram them as I use different locomotives
dwight77