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No I'm not saying it is a horn. hornresp lets you model a bunch of stuff via those horn segments, in this case it's using the horn segments to model a flared port. This is the schematic of that port section alone (with 1 plank removed so it is a 12" opening)



that flare at the end is the expansion as the port opens out to the mouth
 

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With all the planks in place it is basically a periscope. Are you saying it may act more like a horn as one would remove the planks? I'm sorry I'm having a major mental block here.
Visualize the cross-sectional area that the air is moving through as it is exiting the port. As it reaches the last panel that you currently have in place, it is opening up to the room, but still has the barriers of the sub restricting it. As it gets further from the port opening, that cross-sectional area is increasing, similarly to how it would in a flared port. That similar flared port is what @3ll3d00d modeled in HornResp.

I am not an expert, but I don't expect this to actually cause any issues, as this isn't a much different situation from when a ported sub is placed with the port close to a wall. In fact, my ports are firing into a corner which is made up of two walls and an angled ceiling, so it is very much a flared port situation.
 

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Discussion Starter #26
Visualize the cross-sectional area that the air is moving through as it is exiting the port. As it reaches the last panel that you currently have in place, it is opening up to the room, but still has the barriers of the sub restricting it. As it gets further from the port opening, that cross-sectional area is increasing, similarly to how it would in a flared port. That similar flared port is what @3ll3d00d modeled in HornResp.

I am not an expert, but I don't expect this to actually cause any issues, as this isn't a much different situation from when a ported sub is placed with the port close to a wall. In fact, my ports are firing into a corner which is made up of two walls and an angled ceiling, so it is very much a flared port situation.
I get it now. I wish I had the time to learn hornresp.
 

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Discussion Starter #27 (Edited)
Going to go with one port length and simplify. Updated first and second posts to reflect the changes. Can someone verify my port length assumptions? As is, i think it is a 14.6hz tune. I may shorten the inner board to up the tune and get some more spl.

Pete
 

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Few questions you said three port dividers.
So the box is 20 inches wide right so let’s subtract 1.5 inches for the sides. Now you posted you have one slot port rail right? Please confirm
Also what are you putting In Winisd for a rough box size 12 cubic ft.
 

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SideFire Bass Reflex Subwoofer B&C 21DS115

If this is the case

12 cubic ft box
Slot port vent 3” high
17.75 inches wide because you subtract the sides 1.5 inches and the single port rail down the middle.
Slot port length 48” inches long will give you a 14.85 hz tune

Air port velocity is 18.741 at 14.37hz at its highest

And come excursion looks good up to 2,500 watts with a hp added into the mix
 

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Discussion Starter #30
Few questions you said three port dividers.
So the box is 20 inches wide right so let’s subtract 1.5 inches for the sides. Now you posted you have one slot port rail right? Please confirm
Also what are you putting In Winisd for a rough box size 12 cubic ft.
Double baffle so with one port divider it's 3" x 17" x 48". Since I am going to power reach with an iNuke 3k I'm modeling at 1800w but as @Ricci indicated in his write up with @MarkSeatondesign the iNuke 3k seemingly can peak at 2kw. I figure with bracing and driver I am looking at 11.5cuft. I might shorten the inner port board by 10" to give me a 16hz tune and make up a panel and use the kreg jig to install it to extend the port internally if I want more extension.
 

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Double baffle so with one port divider it's 3" x 17" x 48". Since I am going to power reach with an iNuke 3k I'm modeling at 1800w but as @Ricci indicated in his write up with @MarkSeatondesign the iNuke 3k seemingly can peak at 2kw. I figure with bracing and driver I am looking at 11.5cuft. I might shorten the inner port board by 10" to give me a 16hz tune and make up a panel and use the kreg jig to install it to extend the port internally if I want more extension.


You look good I just checked the numbers again via winisd.
 

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Double baffle so with one port divider it's 3" x 17" x 48". Since I am going to power reach with an iNuke 3k I'm modeling at 1800w but as @Ricci indicated in his write up with @MarkSeatondesign the iNuke 3k seemingly can peak at 2kw. I figure with bracing and driver I am looking at 11.5cuft. I might shorten the inner port board by 10" to give me a 16hz tune and make up a panel and use the kreg jig to install it to extend the port internally if I want more extension.
I have a thought for you..... what about doing the bottom of the port EXTERNALLY (see pic). Then if you want to adjust the tune, you just extend the side pieces and port more (or less). Easier to do and you dont need to be as precise...

if the cab will be sitting on carpet, so the bottom will be sealed off, the port can take up some of the otherwise wasted bottom space.


this one is 26" wide including the overhang on the top and bottom panels for aesthetic purposes.


net internal cab volume would be around 8.25 c.f. and tuning would be just under 20hz. going to 2.5" tall feet and a 2.5" port would drop tuning by a couple of hz.











 

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Discussion Starter #33
I have a thought for you..... what about doing the bottom of the port EXTERNALLY (see pic). Then if you want to adjust the tune, you just extend the side pieces and port more (or less). Easier to do and you dont need to be as precise...
That's a neat idea!
 

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That's a neat idea!
Yup. Yours obviously would still be front firing as you designed, but the bottom of the slot port would just be external and would let you adjust things as you want without a ton of extra work. Also makes building the port easier because its just black painted 1x3's lol.....
 

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Discussion Starter #35
Yup. Yours obviously would still be front firing as you designed, but the bottom of the slot port would just be external and would let you adjust things as you want without a ton of extra work. Also makes building the port easier because its just black painted 1x3's lol.....
Only worry would be when it's time to build Moar and stack them.
 

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Only worry would be when it's time to build Moar and stack them.
Not really.... The top of the first one would be used as the bottom of the port for the unit above......

If weight is a worry, make the port a bit skinner with thicker side pieces and middle port brace. The extra thickness of the port supports could be accounted for by extending the ports section a bit to account for the extra thickness....
 

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the slats concept was a cool idea. that could even be done with removable panels of various lengths, so instead of a bunch of slats, there is just a different size panel attached for each different tune. that might make for a more rattle free cab.


once the exit of the port is about 2x the distance from the top panel, it won't really be loading from that any more.


this is roughly how I would think about the port lengths as slats are removed. the second image from the left is the tricky one because the top panel will still be providing a small effect. but by the third image and fourth images there is no loading from the top panel any more, so there is just the port.


slot ports extend 1/2 port length out past the measured length on both ends, which is why the red line is extending out past the apparent end of the port in all cases.


 

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not to any specific port length. just a conceptual.


internal boards for mounting the port panels.


then three port boards. screws and weather stripping should keep everything tight, while still allowing for adjusting the tune. wouldn't be super quick to change tune, but wouldn't be impossible either.







with green port board installed.


 

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Discussion Starter #39
@LTD02 As you increase the tune, port velocity shoots up too. By the time you're at 20hz you need to make the port 4" tall. I didn't realize the port extends beyond the exterior by half the port height. I thought it was just on the interior. Thanks for pointing that out. Would the "virtual length", (ie the internal extension, physical port length and external extension) be what you want to match up as port length in winisd? I need to figure out what length I need for 16hz, I'm thinking that's the sweet spot.
 

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if the port is built for the full height 48" tall cab, then the effective port length (the red line) will be 48" + the port height. so with a 4" port, the effective length will be about 52".





I didn't double check your calculations for internal volume and I'm not quite sure what your plan is with respect to how many port braces will be in there, so I'm not quite sure how deep your port will be.


IF, your internal cab volume is around 11.25 cubic feet (after everything) and your port is roughly 17" deep (20" cab depth - double baffle, one port brace, one rear panel) and 4" tall, then winisd shows a tune of about 16.6hz.
measured results sometimes come in an additional half a hz lower even after all this, so my best guess for your cab would be 16-16.5hz.
port velocity is under 17 m/s all the way down to 18hz with enough power to drive the driver to 15mm excursion, so that is going to be just fine.


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edit: I just checked the cab volume and it looks like 11.2 cubic feet or so with a 4" tall port, so I'd probably subtract 0.5 cubic feet for the driver and bracing for the net internal volume (for winisd).
with no other adjustments that would raise the tuning of the cab (after everything) by about 0.4hz, so call it 16.5-17.0hz tuning.
 

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