I have used only one local, Illinois, shop for all the dcc sound installation in steam locomotives. He is close enough that I deliver the locomotives to his shop and pick them up when he completes the work. The most recent project was dcc and sound in two Bachman Spectrum 2-8-0s. I am delighted with his work. I also had him install dcc sound in two Kato GS-4s. In each case, I provide a Digi-key speaker that I was told provides excellent output. It is difficult for me to evaluate some of the YouTube videos posted by shops of their sound installations. This may be due to the quality of the video audio component. I have Bose speakers on my computer and find very nice sound from YouTube videos posted by JDColombo who participates here.
