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Subwoofer ports confusion?

Old 08-12-2011, 01:16 AM
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Subwoofer ports confusion?

Hey guys, so I need to build a new enclosure for my 12" sub just for a better fit in my trunk.

I know there are plenty of calculators online and making a sealed box is pretty simple but when the ports come into play I get confused and I cant seem to find much info to answer my specific questions online! So here I am to seek some answers

My subwoofer recommends a 1.65cu.ft ported enclosure, so when it is 1.65cu.ft, that would be the net volume of the box but what happens when there is a port? Does the area of the actual port count towards it? Say I build a 1.65cu.ft sealed box, I add the sub, I will minus the volume of the sub, and when I add in a port, do I just subtract the displacement of the wood used to make the port? like is the area of the port that you can put your hand in counted towards the volume?

My second question is my main problem when I come to calculate the port, I was thinking of tuning to about 33hz but on the calculators online, you pick the height and width of your port and it will help calculate your length for you based on your parameters (height,width, volume,desired frequency). So you need the volume to get your frequency...so based on the length of the wood used for the port, it will affect the overall box volume, so how does this work if you wont know the volume of the box AFTER you add the port, which will be less due to the extra wood needed to make the port? So the calculations will be slightly off? Im not too sure if this is clear but its hard to explain.

PRetty much the port length is dependent on the volume of the box, meanwhile once I find the length required, the wood used to make the port (slot port) will now decrease the net volume, so wont the tuning be off ?'

Sorry for the long post but any help will be appreciated
Thanks!
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Old 08-12-2011, 01:18 AM
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oh ya with my box I want to start off with getting the specs right using a sealed box and adjusting it from there with a port to what I desire, so my plan is to make a sealed box but making the face place (where the sub is attached) a bit shorter to leave a gap for the port on one side of the enclosure. And after I straighten my confusion up, Ill make my port length according to the calculator. Sounds good right?
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Old 08-12-2011, 09:53 AM
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okay so I found the answer to my first question about the port, the volume of the port should be subtracted from the volume enclosure correct?
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Old 08-12-2011, 12:21 PM
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that is correct also any internal bracing also needs to be calculated
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Old 08-12-2011, 02:54 PM
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thanks for the confirmation!

Any idea about calculating the port length though and the volume of the enclosure?
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Old 08-12-2011, 03:05 PM
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Don't start with a sealed volume - vented boxes are generally larger to begin with.

Take your box volume and then add the volume of the vent, bracing, woofer to it. It doesn't matter that the overall volume is going to increase, the net volume stays the same.
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Old 08-12-2011, 03:14 PM
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^ thanks ! I was definately over thinking it! You made things so much simpler than I made it !

thanks again! Cheers
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