Confused about port length on planning my first subwoofer build - diyAudio
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Old 24th January 2012, 03:57 AM   #1
JDawg is offline JDawg  Canada
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Default Confused about port length on planning my first subwoofer build

I am thinking of building my first sub so I'm still in the planning stages. I was thinking of using a CSS SDX10 driver and I found a kit for this driver with the box cabinet schematics. Here's the link to the drawing for the box.

http://www.solen.ca/pdf/kits/us10sdx.pdf

I also downloaded Winisd Pro to play around with. The box according to the schematic is about roughly 1.8 cubic feet I think. So I used Winisd and if I input the size of the box plus the port dimensions and length it shows I would get a huge boost around 43Hz. I know that normally you want a flat response so does that mean that the port length indicated in the drawing is wrong?
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Old 24th January 2012, 06:25 AM   #2
mdocod is offline mdocod  United States
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Normally you would want to try for either flattish or even, something with a nice steady rolloff so as not to cause any narrow band of the bass to stand out as prominant (1 note wonder).

The box design you found there appears to be maybe targeted at the crowd looking for nothing but loud, to heck with sound quality, port noise, or flatness. That box with that woofer, IMO, would start making horrendous port noise above ~50-100W in the 30-50hz range. Looks like a car audio SPL oriented build IMO.

Port dimensions on high-Mms drivers gets tricky. Drivers with low Mms and high Vas will require more box size with easy to design vents. Drivers like the one you are eying, high Mms, low Vas, will work in a small box, but the vent size gets enormous to tune the small box low.

To get a driver like this working "well" in a vented box, it is my opinion that the box would have to be ~3-4ft^3 total, with ~1-2ft^3 of that space dedicated to a very large slot port that traverses back and forth a few times to get the length.

Some radical port flares could help reduce the port size some.

If that sounds too large and complicated, I suggest just going sealed and EQing up the bottom end.
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Old 24th January 2012, 06:36 AM   #3
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I was thinking of the necessary acoustic stuffing in the box ....
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Old 24th January 2012, 01:24 PM   #4
bjorno is offline bjorno  Sweden
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Quote:
Originally Posted by JDawg View Post
..I also downloaded Winisd Pro to play around with... So I used Winisd and if I input the size of the box plus the port dimensions and length it shows I would get a huge boost around 43Hz. I know that normally you want a flat response so does that mean that the port length indicated in the drawing is wrong?
Hi,

IMO To model this driver in a ported box when the port has quarter-wave behavior You need a far more potent program than the simple Winisd:

b
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Old 25th January 2012, 05:03 AM   #5
JDawg is offline JDawg  Canada
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Ok I thought there was something wrong with that box. I guess I'll scrap the idea of using that driver to build a sub. I'll see if I can make my JL Audio 10W3V2 driver work in a sealed box.
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Old 25th January 2012, 09:35 AM   #6
Mikey p is offline Mikey p  Canada
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The box volume is 1.5 cu.ft and the tuning frequency is 40 hz. The response is +6 db at 45 hz and -3 db at 33 hz. Solen sells this kit with a Dayton SPA500 amp that has a third order hi-pass filter at 18 hz. There should be an award for the worst ever designed subwoofer.

Last edited by Mikey p; 25th January 2012 at 09:37 AM.
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Old 25th January 2012, 03:30 PM   #7
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Originally Posted by Mikey p View Post
The box volume is 1.5 cu.ft and the tuning frequency is 40 hz. The response is +6 db at 45 hz and -3 db at 33 hz.
Have you measured the cabinet's actual response, or are you using a simulation to arrive at those figures?

What happens to that response curve when the sub is placed near boundaries?
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Old 25th January 2012, 06:00 PM   #8
Mikey p is offline Mikey p  Canada
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That was a simulation from the specs on Solen's website. I did build a sub with this driver with plans from the CSS website. Modeled response as well as in room SPL measurements are here:

CSS QUARTET 10 Sub Kit
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Old 26th January 2012, 05:47 PM   #9
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There's nothing wrong with the driver. The solen design is cr*p. Why not deal direct with the vendor. Creative Sound - Product Details

If you think port lengths are too long, you should think about passive radiators.

It won't take anymore time to do it right than to do it wrong.

Quote:
Originally Posted by JDawg View Post
Ok I thought there was something wrong with that box. I guess I'll scrap the idea of using that driver to build a sub. I'll see if I can make my JL Audio 10W3V2 driver work in a sealed box.
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