Three 2" ports vs One 4" Port? - AVS Forum
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post #1 of 8 Old 08-16-2014, 01:47 PM - Thread Starter
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Three 2" ports vs One 4" Port?

I've realized my ported 12 makes a noticeable amount of port noise around 20hz which is just around its tuning.

Currently it has a 4" port 20" long and flared at both ends. WinISD shows the 4" port at .12ms airspeed which is too high. Changing the port to three 2" ports around 15" gives me .05ms.

So, any reason the 3 ports won't fix the port noise issue? I've read about more surface to air resistance but I can't find any way of calculating how this will impact my design.
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post #2 of 8 Old 08-16-2014, 02:24 PM
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I
Currently it has a 4" port 20" long and flared at both ends. WinISD shows the 4" port at .12ms airspeed which is too high. Changing the port to three 2" ports around 15" gives me .05ms.
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You've got a bad calc somewhere. One 4" port is about 12.5 sq in, three 2" is about 9.4 sq in, so the latter will have higher port velocity, not lower. You probably need to go to two four inch ports, and a larger box as well, otherwise they'll be way too long. BTW, the port velocity isn't measured in milliseconds, so that might have something to do with your error.

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post #3 of 8 Old 08-16-2014, 02:36 PM - Thread Starter
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I'm using the basic version of winisd. I enter the box volume as 3.6 then tuning at 21hz. A single 4" at 18.58 gives me .12 vent Mach. Three 2" at 14.67 gives me .05 Mach. Sorry, ms was incorrect. I can't figure out where my error would be.
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post #4 of 8 Old 08-16-2014, 02:55 PM
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Are you sure you are looking the right place? You should choose "rear port - Air velocity" from the drop down menu. What woofer is it?
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post #5 of 8 Old 08-16-2014, 03:05 PM - Thread Starter
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The interface is different in the basic version of winisd. My laptop doesn't like the pro version. The vent Mach is shown in a box right in the same window with the vent length and number.

The driver is a dayton rss315hf-4 with a dayton 250 plate amp. It sounds good and plays 20hz strong for what it is, but at 20hz the port whistles/squeaks noticeably. At 25hz I get no bad noises.
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post #6 of 8 Old 08-16-2014, 03:14 PM
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Quote:
Originally Posted by Samps View Post
The interface is different in the basic version of winisd. My laptop doesn't like the pro version. The vent Mach is shown in a box right in the same window with the vent length and number.

The driver is a dayton rss315hf-4 with a dayton 250 plate amp. It sounds good and plays 20hz strong for what it is, but at 20hz the port whistles/squeaks noticeably. At 25hz I get no bad noises.

Hmmm ...i have 2 of the 315HO in the same (3.6 cuft net) each with (1) 4" x26" port , powered by a SA1000 , and Never heard any port noise ??
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post #7 of 8 Old 08-16-2014, 03:21 PM - Thread Starter
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I had heard noises all along when watching action movies but I thought it was noises from the room. So the other day I played 20hz test tones to chase down the noises and that when I realized it was the sub itself. There were some rattles in the room I fixed, but the noise from the port is unique. A whistle is the best way to describe it. There is a lot of air blowing out when this happens. My other option is the raise the high pass to bring down the 20hz output, which is not what I want to do.
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post #8 of 8 Old 08-16-2014, 03:54 PM
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Quote:
Originally Posted by Samps View Post
The driver is a dayton rss315hf-4..It sounds good and plays 20hz strong for what it is, but at 20hz the port whistles/squeaks noticeably. At 25hz I get no bad noises.
In 3.6 cu ft at 200w you need two 4 inch ports, each 44 in long. Less area than that and chuffing at 20Hz is pretty much guaranteed. Get rid of WinISD Beta, it's not useless, but almost. Use WinISD Alpha Pro.

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