Hello,
I have 2 SVS 20-39 CS+ subwoofers. With the port plugged they will go to 16Hz. I have left the plugs out because with them in it will literally knock things off shelves upstairs and causes a lot more distracting vibrations in my HT room. Without the plugs, I get deep solid bass with no unwanted effects. I'd say try it both ways and see which sounds better to you. Understand though, you will lose some overall volume by using the plug and tunig the sub lower.