mufflers for around the house use?

These sound like they might work ok, especially if you tacked the 3 chamber version into
a 3" muffler and held it on with one of the above band clamps.

Keep in mind the measurements in the link are from 50' behind the vehicle.

http://www.fordmuscle.com/archives/2000/09/ccinserts/index.php

Here are some decibel measures for relevance.

http://www.tlc-direct.co.uk/Technical/Sounds/Decibles.htm