The current 139 litre volume of the cabinets I’m planning need a two 100mm diameter 24 cm bass reflex ports to tune to my proposed frequency of 33Hz.. Any of the bass reflex tube products cost quite a few bucks to send over to Australia unfortunately. Thanks to the useful suggestions of Stereo.net.au forum members, I got the idea of making my own from PVC water piping, using a heat gun to form the flares. But I’m not so handy with being able to fashion them presentably well, so I went with a combined approach of using some less expensive fixed lenth 200mm long ports (the same kind from Altronics I’ve already used), with some 90mm PVC piping to make short extensions with flaring on the end.
Lucky I still had the offcuts from the ones I had shortened for the Econowave speakers so I could use that to check the dimensions were OK:
It was hard to get them consistantly identical, but I think they will be close enough when it comes to frequency measurements:
Unfortunately, although it is still mentioned on their web page, Altronics no longer stock this model of Bass reflex port. But I was able to find it (model number HP100) on a German web site with reasonable shipping costs – in fact including shipping it came to only slightly mroe than it would have cost for Altronics. They are taking quite a while to arrive here though.
Heating and forming the PVC plastic took a while to get right:
though I was careful to do it all outside in a breeze as I’ve been told the fumes from heated PVC are not healthy at all.
Lucky the jar and milkshake glas were just the right dimensions for forming the shape I was after.