I don't own any of your cabs (yet) Duke, but have always admired your engineering and product offerings. Without giving away any trade secrets, would you be able to share some insights on how you can make a speaker/cab design work as sealed, ported and partially ported? From the little I understand about cabinet design there is usually a "meaningful difference" in the specifications between speakers that would be optimal performers in a either a sealed or ported design. I'm not sure I know of any other cabs that are as effective/capable in "multiple configurations" as yours are. Thanks in advance for whatever you can reasonably share.
Nothing top-secret about it! For starters, I use flared Precision Ports, usually in multiples. The flares help delay the onset of chuffing, and the inner diameters are precisely as advertised, which means I can use off-the-shelf expandable plumber's plugs.
So let's say a cab with a vented-box woofer calls for three 3" diameter Precision Ports (two 3012LF woofers in about 2.6 cubic feet). With all three ports open we get what I think is the "optimal" tuning frequency in this case, about 50 Hz, and we're -2 dB at the 62 Hz first overtone of low-B (and -3 dB at 59 Hz). I like to quote the response at 62 Hz because I think that gives a useful indication of the cab's low-B.
If we plug one port, the tuning frequency drops to about 41 Hz, and now we're -3 dB at 62 Hz.
Plug two ports, tuning frequency is now 30 Hz, and we're -4 dB at 62 Hz.
When we plug ports we're also reducing the port cross-sectional area, which theoretically reduces the chuffing threshold, but we also are moving down into a region where there's typically less energy going into the cab... at any rate, I haven't gotten any reports of plugging some ports resulting in chuffing.
If we plug all three ports, we end up with a low-Q sealed box, -6 dB at 62 Hz (and -3 dB at 90 Hz).
On the other hand, I have a sealed-box-woofer cab being beta-tested at the moment that models -3 dB at 82 Hz (first overtone of low-E) and -6 dB at 62 Hz (first overtone of low-B) in sealed-box mode. Unplug the two ports, and now the cab is tuned to the mid-30's, but in this case most of the boostage happens much higher up. We get a ballpark +2 dB hump from 100 Hz to 200 Hz, and we're now "flat" at 82 Hz and -5 dB at 62 Hz. Also, I would claim a small improvement in thermal power handling from opening up the ports, due to air exchange with the outside world. So imo this is more of a "low-E" cab than a "low-B" cab, with a bit of "free" bass boostage available for outdoor gigs via unplugging the ports.
My cabs are no more "capable" in these various modes than anyone else's would be if they also used pluggable ports, but as far as I know, only a few DIYers have used the technique.
For DIYers who don't want to buy the expensive Precision Ports, just use PVC pipe from the plumbing department at your local hardware store (this way you can test-fit the expandable plumber's plugs in advance). Once you've calculated the length for your ports, measure that length down the centerline and cut the inner end of the port at a 45-degree angle, instead of straight across. This results in an elliptical rather than round opening, for increased cross-sectional area. Two benefits arise: First, the larger cross-sectional area of the elliptical opening improves airflow at this critical location, which is where chuffing would first set in. Second, the port length is now a bit "fuzzy", and this reduces the magnitude of internal port resonances in the midrange region (imagine talking through a cardboard tube). The outer end of the port will be flush with the baffle, and the baffle improves the fluid flow (airflow) into the port, but the inner end of the port has no such benefit, which is why that's normally where chuffing (turbulence) begins.
