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Discussion Starter · #1 · (Edited)
Hey all, I have been modeling this sub based on some serious inspiration from the Marty-Sub, my personal sub exterior preferences, and some numbers from the parts-express UM18-22 product page. Specifically this "Vented (infra-sub): 12 cubic ft. (net internal, not including driver or vent) tuned to 15.5 Hz, with 3 flared vents 4" diameter by 32" long, for an f3 of 15 Hz".

The overall exterior dimensions: 24" wide by 27.75" tall by 42" long.
Internal gross area, including a double walled front panel but without internal bracing or driver volume: 21863.672 cu/in or 12.653 cu/ft
I figure the driver volume plus the internal bracing will soak up that 0.65 cu/ft pretty well to end up really close to the 12 cu/ft number on the product page.

Port/Slot dimension: 21" wide by 3" tall by 20.625" long, with two 3/4" internal braces. Total slot volume = 1206.56 cubic inches
I'm not sure if the slot/port length is correct, but I calculated and modeled it using the cross sectional area from "3 flared vents 4" diameter by 32" long" which equals a total port volume of 1206.36 cubic inches.

The driver will be front mounted, the slot will be front firing at the base of the cabinet.

I was hoping I could get one of you super users to double check this build so far.

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Edit:
My Final design for UM18-22 CANNON

Outside port size: 22.5” W x 3.75” H x 29.25” D
Port volume removed from box volume: 1.355 cu.ft
Inside box gross volume: 12.3 cu.ft
Inside box rough net volume: 10 cu.ft
Inside box dimensions: 22.5” W x 26.25” H x 36” D
Outside box dimensions (w/ double front panel): 24” W x 27.75” H x 38.25” D
Tuned to 21Hz

The graphs are modeled against the two recommended builds from Parts-Express web page (12cf infra-sub & 8cf HT)
 

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Hey all, I have been modeling this sub based on some serious inspiration from the Marty-Sub, my personal sub exterior preferences, and some numbers from the parts-express UM18-22 product page. Specifically this "Vented (infra-sub): 12 cubic ft. (net internal, not including driver or vent) tuned to 15.5 Hz, with 3 flared vents 4" diameter by 32" long, for an f3 of 15 Hz".

The overall exterior dimensions: 24" wide by 27.75" tall by 42" long.
Internal gross area, including a double walled front panel but without internal bracing or driver volume: 21863.672 cu/in or 12.653 cu/ft
I figure the driver volume plus the internal bracing will soak up that 0.65 cu/ft pretty well to end up really close to the 12 cu/ft number on the product page.

Port/Slot dimension: 21" wide by 3" tall by 20.625" long, with two 3/4" internal braces. Total slot volume = 1206.56 cubic inches
I'm not sure if the slot/port length is correct, but I calculated and modeled it using the cross sectional area from "3 flared vents 4" diameter by 32" long" which equals a total port volume of 1206.36 cubic inches.

The driver will be front mounted, the slot will be front firing at the base of the cabinet.

I was hoping I could get one of you super users to double check this build so far.
Plug the info into WinISD and see what it looks like. I just did since I had a similar project loaded, everything lines up. That said, port velocity may be a little high if you push this and will show some compression at the extreme edge of things.
 

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You don't convert round to slit ports by matching the volume. You have to match cross sectional area and length. By having a shorter but wider port, you'll end up with a much higher tuning.

Here's the 15 Hz tune with a 19.5x2.5 port, 10.5 CF, 1800W. Port length would be 44" or so. And for comparison, the same box tuned to 17 Hz on the thinner green line.

 

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Discussion Starter · #6 ·
You don't convert round to slit ports by matching the volume. You have to match cross sectional area and length. By having a shorter but wider port, you'll end up with a much higher tuning.
So the cross sectional area of the original 3 flared vents 4" diameter by 32" long is 37.71 sq.in

If I keep my slot 3" tall I end up with a slot that is 12.57" wide, with overall internal measurements of 12.57" wide by 3" tall by 32" long.
Overall external slot measurements with 3/4 MDF and two internal full length braces: 15.57 wide by 3.75" tall by 31.25" long, capturing 1.056 cu.ft of internal volume.
This port would match the cross sectional area, and length, of the original specifications per parts-express?

I'll need to re-model the rest of the box to be internal net of 12 cu.ft.

Thanks rhodes.
 

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Yeah, that math sounds about right.

How much power do you anticipate feeding this sub? You might want larger than 37.71 sq in if you're going to try and max out its capabilities. The model I posted shows port velocity maxing out at 24 m/s with 1800W using a 48.75 sq in port.

Also note that slot ports often give a real-world tuning slightly less than the models predict; with the slot firing parallel to the floo on the exterior, and the walls of the sub on the interior, those boundaries act to extend the length of the port a couple inches.

Also, don't think that your box has to be exactly 12 CF net internal. You can make it as large or as small as you want and adjust the port dimensions and tuning to suit.
 

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Discussion Starter · #8 ·
How much power do you anticipate feeding this sub? You might want larger than 37.71 sq in if you're going to try and max out its capabilities. The model I posted shows port velocity maxing out at 24 m/s with 1800W using a 48.75 sq in port.
I will be running this off of the HSU 500A subwoofer amplifier which is capable of supplying 800w RMS at 2 Ohms.
 

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Discussion Starter · #9 ·
Plug the info into WinISD and see what it looks like.
I still need to get my feet wet with WinISD. I downloaded it but haven't had time to play around with it yet.


You might want larger than 37.71 sq in if you're going to try and max out its capabilities. The model I posted shows port velocity maxing out at 24 m/s with 1800W using a 48.75 sq in port.

Also note that slot ports often give a real-world tuning slightly less than the models predict; with the slot firing parallel to the floo on the exterior, and the walls of the sub on the interior, those boundaries act to extend the length of the port a couple inches.

Also, don't think that your box has to be exactly 12 CF net internal. You can make it as large or as small as you want and adjust the port dimensions and tuning to suit.
Ultimately I think this sub will be used for 50% HT / 30% normal music listening / 20% heavy bass music listening. So maybe a tune closer to 18hz is where I want to be. I'll do some work in WinISD later tonight.
 

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Different people performed the measurements with different equipment and methods. It's very easy to get variations, depending on drive voltage, use of added mass vs sealed box measurements, the amount of added mass or enclosure size, background noise, woofer breakin, measuring it cold vs warmed up, how the woofer is held down, measured horizontal or vertical, and the specific algorithms used in the software taking measurements and calculating parameters.

Model them both, see the difference, and decide whether the difference is enough to matter. They'll likely be within a dB or two.
 

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Discussion Starter · #12 ·
I think I have the build finalized after modeling in WinISD. I've updated the original post with the info.
 
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