Here is a home made 12/8 port siren by Machine Man on YouTube. I think he has done an awesome job! As far as I know he is the only person in Australia with a siren that produces a perfect 5th interval. The first video he made the 8 port side could only be heard. The second video after he did some adjustments the 12 port side can now be heard.
https://www.youtube.com/watch?v=XZ0-maNuP60
https://www.youtube.com/watch?v=uKWlpLPDl4Y