Going to 6" can increase volume but cause a velocity drop. Going smaller can create more velocity but less volume. It does depend somewhat on air volume to float the particles but too little velocity and the particles will drop out of the airstream. Some guys have mentioned that their intake is 6" split into two 4" (which is close to the same cross sectional area) and they took the splitter off and ran a single 6". For my equipment the 4" lines work for everything but the TS and I don't think going 6" will help with it.I was actually referring to Hank's router(s), Mike, not the vacuum m/c on the Hz issue.
If the vacuum is being used to pull air from the dust collector, volume rather than pressure will be paramount will it not? Wouldn't the design be such as to permit the maximum airflow the vacuum can pull, resistance from pipe diameter and corrugations being limiting factors?
I've been dithering over whether to use permanently fixed 4" or 6" PVC for my 1 1/2HP DC. I keep thinking the 6" is overkill, until I hear contrary opinions.
Maybe the 4" is 'good enough' (?).