In a earlier post I was talking about how my large vintage Goodmans 3 way speakers have a ARU (model 172) fitted and wondered if anyone has had experience with these devices. It's seems that some are saying that these units were basically designed before T&S parameters became available and tube gear was common. As I've moved all my tube gear on (due to high maintenance issues not sound) I find that the high damping factor of modern SS amps might be the reason why ARU units don't produce bass as they were advertised to. I have always had success with ported boxes and wonder if anyone has changed their ARU equipped Goodmans to a more conventional ported design. I've roughly calculated that my boxes are 12 ft3 (330 litres) and will tune them to 35 hz. I'm going to removed the ARU unit and blank the hole with a panel fitted with 2 X 109mm ports, 63mm in length. This way the box hasn't been alterated so that I can revert back in case this doesn't work.