When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
There's no way to get an accurate reading on tuning freq unless you know the length of the port, not just the opening, but how far it extends to inside the box. Since the box is covered in carpet you'll need to take the sub out and measure the port from the inside hole of the sub. From there, if it's just a simple "L" shaped port, you can easily follow directions online and get an est. of the tuning freq. But, if it's a labyrinth style port you pretty much won't be able to measure the tuning freq, unless you take off the carpet and see if the port walls were stapled to the box. Having a ported box is good, but tuning freq. is what makes it run at its full potential, sound and power wise.