large PVC port

Increasing port diameter is usually done to reduce port noise. Unless you are moving a LOT of air at VERY low frequencies, this will be a pretty nifty enclosure for a small sub, but not a good port for a mid-size sub.

When I say a LOT of air, I am thinking rock-concert loud. Or louder.
 
It's definitely useable :D

Be warned, large PVC ports have a seductive nature that can sneak up on you....

You will find that a large dia pipe needs a large box. Here are some figures (sorry about the metric..)

for a port 187.5mm dia and 600mm long:

a tuning frequency of 35hz requires a box size of 111 litres
a tuning frequency of 27hz requires a box size of 154 litres
a tuning frequency of 20hz requires a box size of 300 litres

pipe resonance 286hz

I have built a dual 10inch sub with a pair of 6inch ports in a 130 litre box tuned to 28hz. With 240w applied, this runs with a peak airspeed of a very conservative 8 metres/sec.
A single 7.5 inch port would have run at around 11 m/sec (although it would have needed to be about 1060mm long)

If you flare both ends, I would guess that you could run up to a pair of twelves with about 300w total.
Look for drivers with an Xmax of around 10mm, which will be happy in about 80-150litres each.

regards
Collo
 
I used a 8" X 23" port for a Maelstrom Sonosub, needed that to keep the port noise down. The larger diameter the port the longer it needs to be for the same Fb. I like the sound of larger ports, they seem disappear better.
 

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