I'm building vented speakers with a rectangular vented port. The port is a part of the walls cabinet (it uses 3 walls of the cabinet, the fourth side must be adjusted at the port length needed).
Of course I can use some dedicated software in order to calculate (estimate) the port length.
But, for my intellectual curiosity, I would like to know how to calculate or estimate the end correction of such a vented port.
I can find some rules in the bibliography, but it's always for a round port. Nothing is clear for rectangular port. And it's less clear for a port using walls cabinet.
Can somebody be abble to provide me some informations ?
Many thanks in advance.
Philippe.
Of course I can use some dedicated software in order to calculate (estimate) the port length.
But, for my intellectual curiosity, I would like to know how to calculate or estimate the end correction of such a vented port.
I can find some rules in the bibliography, but it's always for a round port. Nothing is clear for rectangular port. And it's less clear for a port using walls cabinet.
Can somebody be abble to provide me some informations ?
Many thanks in advance.
Philippe.
I am afraid if you are trying a special situation, it is cut and try. There are some rules of thumb out there, like subtract half the height of the slot when using a cabinet wall, but I am afraid the best method is to make it too long to begin with, then measure and adjust. There is nothing really wrong with a port tuned too low, they only become a problem when tuned too high...
That is my feeling too, and this is sort of problematic because rectangular ports are typically more integrated with the box design, making the length harder to adjust.
The end correction for circular tubes comes from the radiation impedance of a baffled piston, and I could imagine that it would be possible to find an analytical expression for the radiation impedance of an infinitely long bar. Has anyone seen such an expression?
The end correction for circular tubes comes from the radiation impedance of a baffled piston, and I could imagine that it would be possible to find an analytical expression for the radiation impedance of an infinitely long bar. Has anyone seen such an expression?
GM said:
I don't think so. As far as I see from a quick look the article is about the air between two surfaces, not outside the port.
Yes very interesting.
But is the end correction formula only for one side of the port ? In this case, the correct value should be the double.
In the paper it's write than the expression is for a rectangular duct ended with an infinite baffle. But in a loudspeaker enclosure, on side of the port is ended with a baffle, but the other side has an unflanged opening (or quite because of the walls of the cabinet on 3 sides).
But is the end correction formula only for one side of the port ? In this case, the correct value should be the double.
In the paper it's write than the expression is for a rectangular duct ended with an infinite baffle. But in a loudspeaker enclosure, on side of the port is ended with a baffle, but the other side has an unflanged opening (or quite because of the walls of the cabinet on 3 sides).
Vent
... maybe this is what you are looking for
Its good for a first calculation
but measurements with LIMP are much more reliable -->
http://www.fesb.hr/~mateljan/arta/download.htm
Regards
Heinrich
... maybe this is what you are looking for
An externally hosted image should be here but it was not working when we last tested it.
Its good for a first calculation
but measurements with LIMP are much more reliable -->
http://www.fesb.hr/~mateljan/arta/download.htm
Regards
Heinrich
Great ! Many thanks !
But by what K should be multiplied ?
For a cylindric port, 0.732 is the coefficient for the diameter.
But for another shape, is it the equivalent diameter that we have to use ?
I have already LIMP. It's a very convinient software. You are right, the calculation is for a first estmation.
But by what K should be multiplied ?
For a cylindric port, 0.732 is the coefficient for the diameter.
But for another shape, is it the equivalent diameter that we have to use ?
I have already LIMP. It's a very convinient software. You are right, the calculation is for a first estmation.
.....
Lv = 10 * c^2 / (16*pi) * D^2 * Np / (fb^2*Vb)-k*D
c = 344m/s
D=diameter of vent in cm
Np=no. of vents
k = correction
Lv = 10 * c^2 / (16*pi) * D^2 * Np / (fb^2*Vb)-k*D
c = 344m/s
D=diameter of vent in cm
Np=no. of vents
k = correction
Hi,
does that mean a K correction makes the port shorter to achieve the correct tuning frequency?
A big K makes the port very much shorter and a liitle K makes it only a little shorter.
If the port projects from both sides of the partition, then presumably 2*K must be subtracted from the calculated length to give the corrected length?
Is there a K value when the port is flush with the partition?
does that mean a K correction makes the port shorter to achieve the correct tuning frequency?
A big K makes the port very much shorter and a liitle K makes it only a little shorter.
If the port projects from both sides of the partition, then presumably 2*K must be subtracted from the calculated length to give the corrected length?
Is there a K value when the port is flush with the partition?
Does it mean that for a rectangular port (for instance the model at the bottom right of your graph) we have to calculate an equivalent diameter D ?
D = sqrt (S/pi) for a rectangular port with S = Width * Height ?
Regards,
Philippe.
D = sqrt (S/pi) for a rectangular port with S = Width * Height ?
Regards,
Philippe.
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