[grsimmon]

I came across an older pair of B&W bookshelf speakers of ported bass-reflex design.  Included with the speakers were foam plugs that the user could put into the ports to change the sound characteristic,  with instructions in the manual for experimentation.  No other controls were present since it was a passive crossover.

So here's my questions:

Can the ports of endless other (passive crossover) bass reflex speakers be plugged as well?  Can a home brew plug be something "forgiving" like a tightly rolled sock,  or would it need to be firm like spray foam, plywood, and/or epoxy?

What are the pros and cons of plugging the ports of a reflex speaker when it was not intended by the manufacturer?   If bass is reduced,  could this be compensated for with a seperate subwoofer?

Thanks for any insight, info or suggestions-  Greg

[Letitroll98]

Yes you can put a sock in it.  (Sorry, couldn't resist)  But yes, socks work great.  You already have the foam plugs for the B&W's so for what other speaker are you thinking of?  I've tried it and never really liked it.  It always seems like you're taking a well designed ported speaker and turning it into a poorly designed acoustic suspension speaker.  It does move the f3 up in frequency and decrease the slope of the low frequency rolloff.  Fun to play with and free to try.  Useful if you have bass resonances at the port tuning frequency. 

[FullRangeMan]

Maybe closed port fit for small rooms.

[JLM]

You can even use a more loosely packed sock to approximate an aperiodic design.  Aperiodic is a sealed/ported hybrid, that use "undersized' ports.  Free to try, but like Letitroll98 indicates it is very hard to design the same cabinet volume/driver to sound good as both ported and less ported.  One exception is Hsu VTF subwoofers. 

Note that some cabinets are so poorly braced that the panels flex enough to act as passive radiators (like ports) in which case whether you plug the port or not may not make much of a difference.

[grsimmon]

Yes you can put a sock in it.  (Sorry, couldn't resist)  But yes, socks work great.  You already have the foam plugs for the B&W's so for what other speaker are you thinking of?  I've tried it and never really liked it.  It always seems like you're taking a well designed ported speaker and turning it into a poorly designed acoustic suspension speaker.  It does move the f3 up in frequency and decrease the slope of the low frequency rolloff.  Fun to play with and free to try.  Useful if you have bass resonances at the port tuning frequency.

The speaker I'm thinking to try this with is Mirage OMD-15 omnidirectional floorstanders.   It's an interesting design in that the cabinet is divided in 2 internally, with a solid divider between, and is both sealed and ported.  The top half is for the midrange and is a sealed/acoustic suspension design, with both a wired mid and an additional passive driver.  The bottom half is for the woofer and the port is located relatively far away on the underside.  I've gutted the insides of the incredibly cheapo pink-panther insulation.  I swear it was actually residential housing insulation.  I replaced it with some fancy sticky-back acoustic foam stuff from Parts Express and cut to size.  It added about 5 pounds per speaker.  I realize that I've likely changed the frequency response,  but to my ears it definitely sounds better than before.   I don't mind reduced bass, so now I'm wondering if it's worth trying to "make" the bottom halves of these speakers into sealed cabinets as well.

[FullRangeMan]

For close BR duct one can use inexpensive tennis ball if size fit.

[Mark Korda]

Hi GR, I just made a pair of speakers out of a David Weems book. They are of a pipe design. The stuffing didn't call for it but I put some Parts Express foam egg-crate at the bottom or throat of the speaker. As far as the sound I noticed this and was not looking for this.
   On the right speaker a bass guitar string was more noticeable than any speaker set up I've had. Most were Dynaco classic speakers with (aperiodic) ports. I used Acoustastuff all thru my speaker and egg-crate at the bottom.
   It was if the bassist was right there and plucked that string. I will not take the egg-crate out because I'm loving the sound and it might just be one of those luck of the draw sound experiments. I'm using a Vifa 6 1/2 inch coax I got a few years ago from Parts Express probably intended for cars.
    Good luck with your project......Mark Korda