Rich,

The Birney does have a speaker cavity. Fred Miller, who is well-known in the trolley community for creating decoder sounds (he did the one for the Con-Cor PCC, for example), also recommended the SDN144, so it looks like that's the one to go for. 

But he recommended shortening the wires between the plug and the decoder body, which involves soldering. Otherwise, there's not enough room in the decoder cavity.  I'll need to refine my soldering skills to do something so delicate.

You're right in the Birney requiring clean track. It's fussy in that regard. But the trade-off is a minimum four-inch radius, so far. I suspect it can handle a smaller radius but I couldn't bend the flex track lower to test it out.

Aurelio

Thanks folks. 

But to clarify, I'm not really looking for the sounds, but for the decoder hardware.

Unfortuantely, the SDN144 requires some soldering. 

And the Soundbug really doesn't fit anywhere unless I remove the current DCC decoder.

Can anyone recommend a sound decoder that will fit inside and work with the Birney?  Preferably something easy to use.