Sound on a 4x8 HO DC layout - Model Railroader Magazine

I think there is a system that can be mounted under your layout that makes the sound seem to follow your locomotives.  It was written up in MR, i think, if not, RMC or MRN.  If  I remember correctly is was conceived for N scale locos that were too small to carry decoder and speaker.  It was not a control system, like the above.

Sorry I can't remember the name or have a better handle on when it was reviewed.

Good luck,

Richard