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Old 11th February 2010, 01:30 PM   #1
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Default Need help judging what to do.

I bought a DIY subwoofer with a monstrous beyma 18G400 inside. Today i sneeked inside it to have look on the construction. It looks like this.http://peecee.dk/upload/view/224324
It got me thinking, cus theres ports in the rear chamber, the front chamber is totally tight. I need help judging whether to build ports into the front chamber or not, since i have never seen a sub cabinet like this before, and i have no idea if it makes sense or not to have a blocked front chamber.

Last edited by sunsse; 11th February 2010 at 01:57 PM.
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Old 11th February 2010, 02:37 PM   #2
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Anyone?
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Old 11th February 2010, 02:50 PM   #3
tinitus is offline tinitus  Europe
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Have a bit more patience my friend
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Old 11th February 2010, 03:04 PM   #4
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Ok, what you have is a 4th order bandpass design.
Adding ports to the sealed chamber would make it 6th order.
Get the thiele small parameyers for said woofer, and play around with different tunings.
As an alternative, you could make it into a quasi-6th order design, by venting the sealed enclosure into the vented one. I know little of this, except you can get good SPLs, but over a pretty narrow frequency range. The SPL competition guys love them for one-note bass.
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Old 11th February 2010, 03:12 PM   #5
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Thanks for you reply. I have been searching, and checked out that 4th order bandpass design. In that particular design, the speaker is turned 180 degrees, compared to what i have. The front of the speaker is turning into the closed enclosure. That is what worries me.
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Old 11th February 2010, 03:18 PM   #6
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I am asking this because is will be some very hard work opening the sub, and turn the speaker 180 degrees (The sub is big, glued and screwed together like nothing i've ever seen before!). I must be 100% sure that it will bring improvements.
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Old 11th February 2010, 03:41 PM   #7
jwmbro is offline jwmbro  United States
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Quote:
Originally Posted by sunsse View Post
Thanks for you reply. I have been searching, and checked out that 4th order bandpass design. In that particular design, the speaker is turned 180 degrees, compared to what i have. The front of the speaker is turning into the closed enclosure. That is what worries me.
Doesn't really make a difference. The woofer produces more or less the same Sounds coming out the front as coming out the back. The only difference is the phase is inverted. So instead of rotating the entire driver, you could simply switch the way the cables are attached (ie, red cable to black terminal, black cable to red terminal). However, if the sub was built by somebody who knows what they are doing, I assume it would have already been attached with the correct polarity.
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Old 11th February 2010, 03:55 PM   #8
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Is that safe? If i switch the polarity, will the speaker be ok at high volumes with big movements, when moving back instead of forward?
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Old 11th February 2010, 04:08 PM   #9
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It moves the same amount forward and backward no matter which way it is hooked up. Besides, switching the polarity won't make any difference unless you have more than one woofer.
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Old 11th February 2010, 04:12 PM   #10
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Okay. Thanks. Great help
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