Well, kind of. It depends on where your intended crossover point will be and the slope of your crossover. Most seem to crossover at 80Hz. At this point having a first port resonance of lower than 110Hz with a 4th order crossover will likely result in audible resonance.The port is to big when the first port resonance drops below 125 hz.
How do you make a port with negative length? :scratch:15 cubic feet @ 55Hz 18" round port: length 1.95".... if that were an SPL wall, a 2" thick baffle
40 cubic feet @ 55Hz 18" round port: length -7.5".... if one were to make a HUGE SPL wall
40 cubic feet @ 33Hz 18" round port: length 2.5"
Ok, that makes sense. But then won't your port output be exiting at the other side of the universe, from a white hole? Seems like it would be hard to keep that in phase with the woofer output, and you'd have light-years of group delay.A very small black hole! :rofl2:
Thank you. Reason I ask, is I started off with a 2.5" x 22.5" slot port, then moved to 6" x 22.5" as it raised the tuning from 13Hz up to 22Hz and brought me from 12.5 cubic feet up to 15.5 cubes... much more desireable....I think he's just asking in a sort of "what if?" scenario. For instance let's say you have a 12" driver and you had a 24" diameter "port" for it. Regardless of length, tuning, enclosure size, real world practicality, etc. At what point does it just become a gigantic hole in the box and cease acting like a port and loading the driver? Does it ever?
Do you know the answer to this?
a lot of excellent info there, thanks! when one needs to use flares to "cheat" and use a smaller diameter, would that imply that at high volume there is a little extra resistence, rather compression? Basically, is it OK to generally say "the larger the port area, the better efficiency, within reason"?I don't know the answer, but can outline my approach....
When selecting port size, I base the diameter on velocity considerations.
The minimum diameter is one that avoids the onset of compression and core turbulence at full power. Next I look at available flaring options to control boundary layer turbulence. If a large enough flare is not available, I move up to the next port diameter.
If the port length gets so large as to drop the first port resonance into the problem range, I look at increasing box size (which will shorten the required port)
I think the car audio guys may have more info on the upper limit for ports. I have sold them a few 10 inch flared ports, but haven't had a lot of feedback...