That is interesting sushi.
I don't doubt that many ported subs when pushed loud enough should produce some amount of port chuff, unless of course the port is 18" in diameter for a 12" woofer.
You are certainly the first person i've heard from that has mentioned this issue with a Hsu sub.
I don't know why the EP350 seems to hit the low notes for me with chuff and yet has not done so for others using similar settings.
You are right in that the best way to determine whether your sub will produce any amount of chuff is to use a quiet but low note passage from music or dvd (LOTR- Mines of Moria --goblin drums works well for my example).
Keep cranking up the gain on the sub until you hear it and you will get an idea of how much it takes to produce the chuff.
Using the LOTR piece, i can produce chuff using a volume settings as low as 25% on the EP350.
