Originally Posted by
Jim A Walters
John,
I did a quick experiment with it. I had my 4" flexible hose not connected to anything and started it up. Once it was up to speed I slid it on the connector for my router table which has roughly a 2" opening. I could definitely hear it ramp up to a higher pitch. I then pulled it off with it still running (which isn't real easy by the way), and I could hear the pitch go lower again.
I'm not sure how to really interpret that though. You get the same affect if you run your household vacuum and then block the end of the hose. The motor will rev up but I think it's just doing what Steve said, just spinning the air inside the vacuum with less resistance and therefore the motor is able to run faster.
I wish I had an ammeter to measure what's going on. It's a bit hard to tell from just the sound.