Hi,
I am building a pair of subs using 2 x Omnes audio subs with 12mm Xmax,
So far the build has gone good but now I'm kind stock as I was planning on using a squareish slot port raised 2 cm from the floor, a rectangular port might be the right word.
Anyway, I have now changed my mind and want to build a ordinary bottom slot using bottom and both box sizes.
The area is 100cm2 and width 23,3 cm and height 4,3cm.
How long does the port have to be when calculating using this German paper? I ask because my math sucks and formulas are out of my league.
Here is the paper, I'm building as we speak so if anyone can help fast it would be very appreciated! I only have today on me to build the boxes and one is half finished, the other in parts.
I thank you for the help in advance! //JK
I am building a pair of subs using 2 x Omnes audio subs with 12mm Xmax,
So far the build has gone good but now I'm kind stock as I was planning on using a squareish slot port raised 2 cm from the floor, a rectangular port might be the right word.
Anyway, I have now changed my mind and want to build a ordinary bottom slot using bottom and both box sizes.
The area is 100cm2 and width 23,3 cm and height 4,3cm.
How long does the port have to be when calculating using this German paper? I ask because my math sucks and formulas are out of my league.
Here is the paper, I'm building as we speak so if anyone can help fast it would be very appreciated! I only have today on me to build the boxes and one is half finished, the other in parts.
I thank you for the help in advance! //JK
Attachments
They are 8" with 12mm xmax one way.
Every calculator i try online gives me different numbers.. i would like someone who has done a slot port and measured it after if that calculation he used worked as it said it should.
Or is there any thumb rule? Ive read to shorten the slot by half the vent. But vent height or vent width?
Every calculator i try online gives me different numbers.. i would like someone who has done a slot port and measured it after if that calculation he used worked as it said it should.
Or is there any thumb rule? Ive read to shorten the slot by half the vent. But vent height or vent width?
Port area seems too small.
You want 1/3 Sd min., for that high excursion drivers a even higher number won`t hurt.
Slot ports, especially on walls can`t really be calculated exactly due to port losses depending on width and other factors (driver tolerances, wrong tsp...)
I would use a port calculation and just divide by 1.2 then measure/listen and maybe cut the length even further until it fits.
I had never the case that a port calculation will exactly fit.
Alternatively you could use (a) adjustable variable length round port(s).
Although a single slot port will sound better (to my ears).
You want 1/3 Sd min., for that high excursion drivers a even higher number won`t hurt.
Slot ports, especially on walls can`t really be calculated exactly due to port losses depending on width and other factors (driver tolerances, wrong tsp...)
I would use a port calculation and just divide by 1.2 then measure/listen and maybe cut the length even further until it fits.
I had never the case that a port calculation will exactly fit.
Alternatively you could use (a) adjustable variable length round port(s).
Although a single slot port will sound better (to my ears).
"Driver tolerances" will not affect Fb, which is solely dependent on the box and the vent.
Frictional losses along the vent may affect the "Q" of the resonance, but I'm not sure that they will affect Fb. If they did, neither of my two recent projects would have hit the target Fb - they both use slot vents. They are also configured as MLTLs rather than slot-loaded vented boxes.
I have another project, an old one, where the resulting Fb simply does not match the sim, and that project used flared round vents. When I get some time, I'll post it up here as a curiousity, as I still haven't figured out why it differs so much from the corresponding Hornresp sim, and I'm not talking just about Fb.
Anyway, I suspect that how the vent is terminated in the box has the largest impact on the difference between sim'd Fb and actual Fb. With an MLTL configuration, well at least the type that I use, this issue is avoided.
You are way overcomplicating things. I told you before that the end correction image you seem to think is correct is not.
I have measured a couple slot port resonance frequencies and they didn't measure any different than the equivalent round even when the slot was on the bottom of the box.
Take your area, turn it into an equivalent round, and do this:
To tune a volume Vb (in liters) to a frequency Fb (from Small-Margolis again)
Lv = 2350*Dv^2/(Vb*Fb^2) - 0.73*Dv
Lv and Dv are vent length and diameter in millimeters, Lv is assumed to be larger than 50mm for this formula, so if it comes out shorter, pick a larger Dv.
If you measure Fb and find it to be different from the predicted value, you can figure out how much to add or subtract by calculating:
deltaLv = -deltaFb*Dv^2*2350/(Fb^2*Vb), where deltaFb = Fb_desired-Fb_measured.
A Typical port for this woofer would be 81cm^2 (4" round equivalent) and roughly 72cm long. This is assuming you have a ~25L box tuned to 35Hz. The length is what you have to deal with when tuning a small box to a low frequency. Maybe you should forget the vent and go with a passive radiator.
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.