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Discussion Starter #1
When is the cross sectional area of a port too big compared to driver Vd? I assume it is based soley on Vd, as a small driver with large excursion may move the same or more air than a larger driver with less excursion.
 

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The port is to big when the first port resonance drops below 125 hz.
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.
 

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Discussion Starter #4
So basically the only issue is port length...port tesonance/1st harmonic.

So if someone were to build a really large enclosure and tune really high for SPL burps, say big enough and high enough to make the port the same size as the sub.... no issues there... the port would act as a true port?
 

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Why not? But it would be a very very long one most probably :unbelievable:
 

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Discussion Starter #6
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"
 

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Jordan,

Nobody makes anything like what you wrote above, moreover you must have something wrong with your calculations (I think).
 

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The calculations look fine, port length is short because of the higher tuning.

I still don't see any point to this. At the frequencies targeted a high efficiency pro driver would be more suited to a reasonable solution to high SPL application.
 

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No need to have a 40 cuft enclosure tuned that high!! It doesn't make sense to me...
 

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Discussion Starter #15
so i am guessing the answer is no. no, there is no limit to the size of your port diameter. if you want to make your port 1/2, or even 3/4 the size of your driver, go right ahead.

thanks guys!

krypto
 

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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?

Collo,
Do you know the answer to this?
 

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Discussion Starter #18
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?

Collo,
Do you know the answer to this?
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....

Then I decided to go sonotube port... 8" or 10". I have an IB18 on the way, and a 10" port would seem to have less port compression, so more sensitive so to speak, less restriction.... but is 10" getting too big?

Now.. only 1 person here has said "YA!" to me tuning sub 25-35Hz...

So as you say WHAT IF i went with a 12" port or even a 16" port to raise the tuning to said 25Hz-35Hz which would lower the 18 cubes I now have opened up to say 12-15 cubes... more suitable for car audio, and a super huge port for when I drop a 21" or 22" beast in there


:dontknow:
 

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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...
 

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Discussion Starter #20
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...
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"?
 
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