A few things:
- The more noise coming out of the tube, the less in your house
- if you are able to run another angle at the end of the pipe, you can bounce the noise coming out the tube down to a soft, noise absorbent material on the ground
- wrapping the portion of the tube thats inside the house with bubble wrap or insulation will massively reduce the noise you hear inside (I am one with the Forge, the Forge is one with me)
I personally prefer the more rigid/smooth interior walled tubing because it keeps the sound in better, and keeps cfm higher.