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Discussion Starter #1
1. Do you subtract the port area from the internal volume of the box? Sounds stupid, build hundreds of boxes was never really sure. Want to do external ports.

2. Is it necessary for the ports to exit on the same side as the woofer face. I am concerned about phase cancellation. Is this crazy????

3. I am installing 2 Morel Ultimo 10". It was my thought I would do a mono box (both drivers in a common chamber, properly braced). Does this mean I can get away with 1 port (2X) the size of spec?

Thanks for any suggestions, this is a really tough box based on application. Just dont want to spend the time to find out its f-ed.

~JH
 

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1 Yes. Bracing, port’s and driver’s displacement must be subtracted.
2. Distance between frontal and rear panel is much smaller than the sub’s operating wave length and the difference is minimal here. Another question is the port resonance. Port resonance jointly with the speaker output gives the spike and fall at response curve.
I didn’t dig its scientific roots but noticed that with frontal went this spike happens before the fall. In other words if you have long port the rear went would be better.
3 By combining two boxes you can use 1 port of the same length but with two times bigger port’s internal area not diameter.
 

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-If you're doing external ports, they won't figure into the internal volume.
-Common sub chambers are usually preferred.
-I personally like my ports at a 90* angle to the sub orientation.
-If it calls for a single 4" (for example)for one sub, you can use (2) 4's or a single port of equivalent surface area. Which would be a 6" in that case. 4" is ~ 12sq in. a 6" is ~ 28sq in. If you had just doubled the diameter (2 x 4" = 8"), then it would be 50q in and most likely need to be 3ft long to achieve the tuning you want. Lol.
 

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Discussion Starter #4
Thanks guys for the info.....


Here is a basic concept of the box in question.

The rear seat of my truck is a like a 70/30 split. This split opens independently


Although the pic doesnt do a great job showing this, shown at the top of the goofy OEM JBL sub box is the frame support for the passenger side seat. It is my intent to use the area just in front of the support for the external ports (*they will still be completely under the seat as the support is about 10" under).

Any comments about this box I am suggesting????

Tks,

~JH
 

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This design has rights to live. Big problem for long boxes is the standing wave. The resonance of that wave becomes significant at quarter wavelength, and peak is at half wavelength. To avoid the boxy sound there must be used braces and materials for acoustical dampening. Symmetry and parallel surfaces are usually bad thing for boxes but in current design speakers are placed too radically. They aspire to work like short transmission line. I’d put one speaker nearer to the center.
Something like this.

 
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