BobH wrote:
Thanks for the information Everybody!

The main reason I was looking at the screw type compressor was for the
quiet operation. The compressor lives in the shop with me and I want
something as quiet as reasonably possible. Putting it outside or in a
separate room are not really options for me. Currently, I use an old
Speedair that is so noisy that I almost never use it. The oil-less ones
are worse. I need something to keep up with a small bead blast cabinet,
but if I had a compressor that did not chase me out of the shop, I would
use compressed air a lot more.

Are low RPM compressors available as small as 5 HP?
I've never heard a rotary screw that was truly "quiet". They
make a totally different sound, more like a hum than a
chug-chug, but it really isn't that quiet. They do put
sound-absorbing huts around them to reduce the hum. I have a
small Quincy, and it was pretty quiet with a 1 Hp motor on it at
450 RPM, but when I upped the motor to the design rating of 2
Hp, and changed the pulley for 915 RPM, it got surprisingly
QUIETER! I think the intake valves were rattling at the lower
speed. This is right in the shop with me, and with no acoustic
cover or intake muffler. I think you could cut the noise quite
a bit with a very simple muffler on the intake, just like a
coffee can with some holes in it or something, but I haven't
bothered.

I do wear an ear protector when I will be in the shop with it,
but I usually wear that anyway when working with the machines.
If I put a sound damping "house" over it and an intake muffler,
I think it would so quiet I wouldn't need the protectors.

Jon