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Discussion Starter #1
I am trying to design a vented box for a DIYMA 12" sub using WinISD. I read threw the tutorial that this site offers which helped out alot. I have few questions that it did not cover though. I am trying to tune it at 30Hz and it seems to want 30L for volume. Which is really small, evidently these subs like small enclosures. So now for the port, I am wanting to build a rectangle rear port. I understand I want to keep the port resonance at or above 120Hz and the port air velocity needs to be no higher than 25 m/s. But I am not sure what the "cross area" should be at or what the "end correction" number means. Also why is it that the bigger W and H I make the vent the longer it has to be, you think it would be the opposite.
 

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If you go to the "vents" page and click on the shape icon, it will change to a square and allow you to enter slot dimensions.
 

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Cross section is the square footage or inches of the opening. A 8" x 2" slot port would have a cross sections of 16 in^2.

End correction takes into account a flair at both ends of the port. I am guessing a 3/4 roundover would be .75 and so on. I could be wrong tho. I usually just leave it on whatever the default is.
 

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Cross area is how many square inches of surface area the port has. Too small an area and you get port noise. Adjust the size so the port air speed stays under 26 m/s.

End correction is about the acoustical length of the port as opposed to the physical length of the port. There is a description of it in the Help files. Click on Contents - Articles - Port Terminology.

Is this for a music sub and could you post the parameters of the sub?
 

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Discussion Starter #7
Thanks for answering that for me. I am trying to figure out how to make a vent it calls for roughly 48in long vent. But the box volume is only 1.05 cubic ft. Is it ok to make the vent turn 90 or 180 degrees or does that mess stuff up. I would need to snake it in there to get that length.
 

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Discussion Starter #8
Here are the specs, sorry I missed that you requested them. Yeah this is a music sub and for movies too.

Specs:

* Acceptable enclosure size: .25 to 1.5cft sealed box (larger enclosures INCREASE powerhandling)
* Acceptable amplifer power range: 200 to 1000 watts per sub
* Recommended for typical SQ use: 1cft + 300 watt amplifier power
* Single 4 ohm voice coil
* QTS: .354
* FS: 25hz
* VAS: 41.7 L
* RE: 3.6 Ohm
* BL: 22
* SPL: 84.3 dbwm
* Le: 1.3mh
* Xmax: 23mm 1 way (71% bl, 25% cms)
* Xmech: 64mm peak to peak
* Weight: 37 lbs
* Cutout diameter: 28cm
* Mounting depth: 16cm
* Driver volume: .15 cft
 

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Discussion Starter #11
I should add that I will be using a Crown CE 2000 amp for these. It puts out 660watt at 4ohm per channel.
 

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Discussion Starter #13
The corners you are referring to are the outside of box corners or the vent corners. Also can i vent out the front or does it have to go out the back. The reason I ask is it will be easier to wrap a 42" vent around the box and vent it out the front under the sub woofer.
 

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Discussion Starter #15
I dont think my amp has a high pass filter built in it. Would you still recommend these specs without one.
 

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Discussion Starter #17
Would you recommend the EP2500 or the EP4000 for a good sub amp. I am looking at them because of cheap, lots of power and they have the lowpass filter.
 

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Discussion Starter #19
I just dont have the extra money for a high pass filter right now. Is there any other design I could do that would not involve one. I slapped a 1 cubic ft box together this weekend and fed it 600watts, I have to say it was not to loud. Then I popped a 3in hole in it and ported it with a couple feet of PVC just to see the difference. There was alot but way to much port velocity, much louder though.
 

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...End correction takes into account a flair at both ends of the port...
Not true.

WinISD only knows about flanged ends, not flared ends. Flanged is where the port ends through a wall.

Here are some examples....




Drawing from this WinISD page.

WinISD needs the effective length of the port, which is the physical length less one half of the flare radius for each end that is flared.
 
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