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post #31 of 43 Old 04-18-2017, 10:16 AM
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Hey @winty82

As far what port tune and box frequency your subwoofer will be built with, that's up to you. If you look at the VBSS thread it has 3 options: 15Hz, 20Hz and 31Hz. It seems like most people use the lower tunes, especially if these subs are their main subs. 20Hz seems like a good place to start so that's what I used to find port dimensions for you.

With your box dimensions giving approx 7.4 cubic feet interior volume: For a 20Hz tune your port could be 2 inches tall, 26 inches wide (27.5 total with two rails in the middle) then the port length would be ~41 inches according to WinISD. So if your cab depth is 20", the port would run along the bottom for 19" then turn up and run along the back for 22" before opening into the cab. WinISD doesn't really account for effects that lower port tune when using a slot port like this, so it's likely your tune would come out slightly lower than 20Hz in real life, perhaps 18-19Hz. Not much, but enough to consider.

Then of course you need to apply the HPF and other EQ in the iNuke DSP to get a flat response. As you can see in the graph, these aren't flat out of the box.



There are many other port designs that can give you the same tune or different tunes. If you keep the port height at 2", then for example a 41" long port that's only 15" wide would you give you a 15Hz tune. A port that's 26" wide and only 13" long would give you a 31Hz tune.
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post #32 of 43 Old 04-18-2017, 04:52 PM
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One caveat though, and maybe you saw this post by LTD on one of the threads I linked to earlier:

Quote:
Originally Posted by LTD02 View Post
and for guys who may be following along, the PA460 isn't the best for a low tuning home theater unless 4 or more drivers are used and even then if going into a medium-large theater 8 drivers would be even better. :-)
Since you're in a small room, your output down low might be decent, or it might not, since that's not really what these drivers are designed for.

Here's a thread by @keith1297 with some of his impressions down in post #21 , so even in a big room a pair of these can sound good, you might just want to have low expectations for super LFE from these.

Subwoofer Selection ...

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post #33 of 43 Old 04-18-2017, 07:49 PM - Thread Starter
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@Brazle Thank you very much for your input.

I'm under the impression that these will be a huge step up from the single 10" sub that I currently have so anything better than that is going to be a huge bonus!

From my very limited understanding, the lower the Hz, the better I can hope for from movies.
I'll try and sketch a design up this evening using the port dimensions you've kindly provided to confirm I've actually understood.
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post #34 of 43 Old 04-18-2017, 09:41 PM - Thread Starter
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So after a very quick sketch up, does this look correct visually?
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post #35 of 43 Old 04-19-2017, 03:35 PM
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That looks really good. Just, FYI, with a 2x15" port there's a chance if you boost the low end much and you play at high volumes, you'll get some port noise. The port is on the smallish size, though bigger than the 4" diameter port on the original VBSS. Flared round ports are less susceptible to port noise though.

With no EQ, only HPF at 15Hz, port air velocity at 15Hz is below 12 m/s which is fine. Once you add any boost at the lower end, that air speed shoots up though. As high as 45 m/s.
If that's something you're worried about, you can look into a bigger port to help keep that from happening.

You could ask those others who have made these cabs if they have any trouble with port noise, I'm not sure if it's an issue or not.

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post #36 of 43 Old 04-19-2017, 04:41 PM - Thread Starter
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@brazzle

Would a taper design assist in reducing port noise?

Like this?
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post #37 of 43 Old 04-19-2017, 05:08 PM
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Quote:
Originally Posted by winty82 View Post
@brazzle

Would a taper design assist in reducing port noise?

Like this?
Why not simply widen the port?

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post #38 of 43 Old 04-19-2017, 05:11 PM - Thread Starter
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Quote:
Originally Posted by Rowan611 View Post
Why not simply widen the port?

Lol well yes that'd likely be the simpler solution, I suppose I was thinking of slowing the air down as it leaves the enclosure? Kind of venturi like
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post #39 of 43 Old 04-19-2017, 05:20 PM
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Quote:
Originally Posted by winty82 View Post
Lol well yes that'd likely be the simpler solution, I suppose I was thinking of slowing the air down as it leaves the enclosure? Kind of venturi like
If it were me; I'd widen the port and use a 1/4" - 1/2" round over bit to taper the port. Best of both worlds.

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post #40 of 43 Old 04-19-2017, 05:28 PM - Thread Starter
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Quote:
Originally Posted by Rowan611 View Post
If it were me; I'd widen the port and use a 1/4" - 1/2" round over bit to taper the port. Best of both worlds.
So the current design above has a 15" opening. Do we think 18" would be sufficient?
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post #41 of 43 Old 04-19-2017, 05:35 PM
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Quote:
Originally Posted by winty82 View Post
So the current design above has a 15" opening. Do we think 18" would be sufficient?
Just re-read what Brazle typed above. I would shoot for a 20hz tune. Make the width of the port 26", height 2" and 41" long. I wouldn't port these for a 15hz tune. It's your call obviously. But, a 20hz tune in a small room with some room gain; I think you'll be very impressed.

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post #42 of 43 Old 04-19-2017, 06:39 PM - Thread Starter
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Ok. So attached is the design with the 26" wide port with a total length of 41".
I've added some bracing as well, and will likely add a little more during construction.

Many thanks for all the help.
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post #43 of 43 Old 04-19-2017, 06:42 PM
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Looks good!

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