Ittproducts.com offers static sound modules for a variety of purposes, and I bought for for diesel track sounds. Has anyone ever used or bought one of these?
I have DC, so I don’t have an option for on-board engine sound, especially for N scale.
The following 4 sound decoders work in DC AND DCC
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QSI
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Sountraxx Tsunami
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ESU LokSound 3.5
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MRC Brilliance decoders work in DC AND DCC.
Of the 4 above, Soundtrax Tsunami mini (TSU750) and ESU LokSound Micro should fit in a good number of n scale engines. Speakers come as small as 3/8"
Only the QSI can be programmed on DC track. However the Soundtrax Tsunami can be programmed for automatic turning of bells on and off, blow whistles at grade changes, and starting/stopping. But you need to program it on sombody’s DCC system first. 
Edit: Come to think of it, the DC mode is off by default on the Tsunami’s. (If I remember correctly) So you’ll need to find someone with a DCC system any way. Isn’t that a chicken and the egg problem?
Pretty much. 
I might have to check into the Tsunami decoder, as if that would fit an N scale DC engine, I might have to pick that up.
Just bought a 5/8’s inch x 1 3/8’s inch pair of 8-ohm laptop speakers to hook up to my sound module from ittproducts.com. I plan on putting the sound module in a building and the speaker in the same building to make it all inclusive. I have a rocker switch that I will wire in line with the positive lead going to the battery. The sound module also has connections for a momentary push button switch, which I just bought from Radioshack. The power source will be its own 9V battery.
Gart, can you fix electronic equipment? I have one of the MRC thingies that make Steam sound, crossing gate sounds etc. It works till you turn it off, to get it working again you have to turn it on and off 20 to 30 times to get it to works again. Could just use a good cleaning.
You can have it, I have went sound and have not used it for years!
PM me and we will work out the details.
Cuda Ken