Tom - Great article on your revitalized shop in Classics. I applaud the idea of using metal pipe in the compressed air system. Metal is much safer than any plastic. I noted you located the noise generator, aka compressor, outside. This might work in Florida, but up here in the occasionally frozen North compressors have to be kept warm or the condensed water mucks up the works. They can be quieted considerably by piping the air INLET to another room or to the outside. A friend did that in his truck repair shop and the results are you can hear yourself think while the compressor is compressing.
GregW
