Take out port to lower resonant frequency

Richard Stringer

Jan 13, 2011
Boston, Lincolnshire, UK
Hi ya guys I have four Wharfedale Delta 218B dual 18" subs and i've been using them for years and like them but they struggle with very low bass so I was thinking about taking out two ports in each driver chamber and then sealing up the ports and changing the drivers with RCF L18P400 drivers instead. I can't afford subs with lower bass so would taking out two ports and then sealing up the front holes of the ports enable the bass to be deeper? Or could I just seal up two ports without taking the port out?

Here are the subs in the photo below and as you can see they have four ports per driver which are big and not very deep so regardless of what the specs say they're about -3db at 50hz.


Randy Gartner

Jan 12, 2011
There is so much involved in designing a speaker cabinet. The cabinet volume and the ports are designed around the particular driver you are using. You need to look at the specs for the new speakers you want to use to see if they will work in the cabinets you have. There are a few books and some online articles that you may want to look at so you have a better understanding of what a port is for and how they are used in tuning the cabinet for certain frequency response.
Oct 25, 2018
Bideford, Devon. UK
Blanking off two ports will indeed reduce the resonant frequency of the box. It will also halve the port area (and triangular ports are about as bad as they get anyway) thus reducing port output, whilst dramatically increasing port distortion and compression. The upshot of the modification you suggest will be greatly reduced output just where you want it! An 18" in a little box like that cannot ever go particularly low anyway. There's just no getting away from the physics...
Triangular ports are made for one reason; well, possibly two - cheapness and/or ignorance. Please folks, don't do it. There are plenty of good papers on the 'net showing how it should be done.

Peter Morris

May 8, 2011
You are correct that triangular ports don’t perform well, they have a large surface area compared to the volume of air they contain; but there are some advantages to corner ports like these. If you need to minimize the weight of the box while providing bracing to the walls, it’s a very effective solution. They also allow for a very small box frontal area which can be advantageous in many situations.