Of interest
http://www.piteraq.dk/flight/muffler.htmlThe swiss style muffler
Note the original author Tony Bingelis
Aluminum round downspout is available in the US (home depot)
I have 100' of 3" here at home waiting for me to put on my house
It is fluted or corrogated as in not smooth; but it is available in smooth.
Tom XL-7.
the swiss mufflers are very long but effective
Perhaps a shorter version would do.