Some have had adequate noise reduction using a 25 lb propane bottle.
The idea I wanted to try was to have 2 bottles in series creating a first stage expansion, and then a second stage expansion.
I purchased two 5 gallon portable air compressor tanks and with the help of a welder friend, added a few threaded ports so that the two tanks could be screwed together.
Also added were 2 threaded ports for inlet and outlet.
The outlet port is oriented to allow a vertical stack to be added.
Below are pictures during construction....
Here are two videos of the tests that I ran.
I must point out that in both cases there is also an automotive muffler at the engine (which are almost useless on their own).
First is a test with the listeroid. I did this test before finishing and painting the unit in case it was a failure.
It turns out that the muffler did a fine job of almost eliminating the noise. (Neighbours cannot hear it)
https://www.youtube.com/watch?v=vRx_mrKnouUSecond test was after the unit was completed and connected to a changfa engine running at 1150 rpm.
You will note that the engine is mechanically loud indoors, but outside the muffler is extremely effective.
https://www.youtube.com/watch?v=EefDlxHy1uU<click on pictures to enlarge>
Veggie