Blocking Ports on Ported Speakers

Hello,
I would recommend treating the room and not the speakers. If they are rear ported put some dampers behind the speakers on the wall. Build a frame with 1x4 or 1x6 wood boards. Hone Depot will cut them for you and put mineral wool insulation inside with some cheap fabric over the front. Home Depot sells Viagro burlap in the garden department for $10. When you can swing it get some GIK diffusers and/or bass traps for your room. Treat the room and not the speakers. You will be amazed by the results. YouTube has a bunch of DIY stuff. It works at about 65%-75%. Amazon sells panels for about $30-$40 per 2x2 panel. If you want to know what it will sound like look up near field listening. Pull your speakers out about 4’-6’ from back wall, put about 4’-6’ apart put a chair 5’-6’ in front of speakers. Take a listen. Please let your speakers breathe. Also, get your first reflection points covered too. 

As I understand it, as one blocks the port it flattens the roll off of the bass such that the roll off starts at somewhat higher frequency but extends the bass  -10dB point. 

Sealed cabinets (acoustic suspension) are known for tight bass, although bass extension is rarely as good as with ported designs (Bass Reflex). But no free lunch here: Ports require careful engineering and making good trade offs. Very easy to have ported designs that produce wooly, bloated, very ill-defined bass.

IN BETWEEN these designs you have the resistive port. This is what the OP is doing with the pillows. You get tighter bass like sealed, but better bass extension like ported. It damps the resonance peak of the woofer due to resistive air load. It’s called an “aperiodic” loading of the woofer.

Dynaudio in the 1980s sold a resistive vent called a “Variovent”. You can Google it.

A previous poster said that the cone doesn’t return before the next signal. That statement is total BS!! Air inside the cabinet always resists the woofer cone from moving out of its center position. When it moves out, it forms a vacuum pulling the woofer cone back to center. When the cone moves into the cabinet, air resists it and wants to push the cone out to its natural center position. BS that the cone can’t or won’t be able to center itself.

You could also try plastic straws in the port. ProAc used them for a while. I think that the idea was that it provided some resistance without completely sealing the port.

Usually the sweet spot is how the speakers is without a port blocked.

Ports are designed specifically by length and diameter to extend the bass response by a "tuned" tube that resonates at a specific group of frequencies. You are a speaker engineer and your speaker plays naturally to 100Hz.  Put a port in that has a center resonance (or bass boost) at around 85Hz, the total speaker now sounds like it goes lower than the 100Hz, the port is "extending" bass response downward.

Think of a long tube you blow into at a football game and make a loud low frequency howl- this is the port tube demonstration. The frequency of the boost depends on the length and diameter of the tube.  [Passive radiators do the same thing].  Allow this tube to boost everything moving through the speaker and it sounds like it has lots of bass when the main driver isn't producing that much bass at all.  This is the bose trick that works brilliantly in some of their models.  

Stuff the port and you usually move the roll off (the lowest frequency the speaker reproduces) UP, reducing total bass from your speaker. In one speaker I import, it comes with foam port plugs and was designed to use this port stuffing feature to make it more linear for those that prefer this sound vs those that prefer a little bass bump down low to sound better on pop music or EDM or whatever.  When the speaker is designed with this in mind, its a good thing.  But this is rare- I have heard of few speakers where port plugs are part of the feature set.   

Many cheap speakers are so poorly designed that the boost from the port is huge, excessive, because manufacturers know people buy the speaker "with more bass".  So in this case, plugging the port makes the speakers sound totally different- and may remove all the [perceived] bass and suddenly make your speaker sound thin and all midrange and top end.  These areas are generally unaffected by ports and remain the same no matter what the port does or does not do.  

Brad. .

OP remember restricting the port works both directions on the driver, when you restrict the port the RETURN to center is slower. That literally puts the voice coil in a forward position while receiving the next signal.

The better solution might be to replace the dampening in the cabinets and add a thicker strand of HEAVY fiberglass. Sometimes the heaver batting and or more of it might really surprise you.. BTW keep the batting AWAY from the drivers.. I use burlap to cover the backs of the drivers..

Burlap can be a good port plug. Maybe Parts Express for foams.

Regards