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Old 03-06-2016, 11:38 PM
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Default question about bandpass boxes

I have 2 sundown x18s could i just use the ported box design sundown provided an just build an sealed part on top to make it 4th order (i think the ported was tuned at 35 i want to be at 28 on ported part) really hoping to learn more about 4ths from you guys

Last edited by Maniac; 03-06-2016 at 11:42 PM.
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Old 03-06-2016, 11:41 PM
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Meant to say 4th order
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Old 03-07-2016, 03:13 AM
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Quote:
Originally Posted by Maniac View Post
I have 2 sundown x18s could i just use the ported box design sundown provided an just build an sealed part on top to make it 4th order (i think the ported was tuned at 35 i want to be at 28 on ported part) really hoping to learn more about 4ths from you guys
no.. One thing about 4th orders is they roll off very different than ported.

ported boxes have a 4th order roll off below tuning. So below tuning they roll off at 24 db/octave. So if you tune at 38hz, it'll be 24db down at 19hz, not including your cabin gain. Because of that, if you want lows, you tune near the lowest frequency you want to be able to play, or at least in the ballpark since cabin gain can help you. On the top end above tuning, they act more or less like a sealed box, minus a bit of help within 1/2 octave of the ports tuning.

4th orders also roll off at 24db/octave total, but it's 12db per octave below tuning and 12db per octave above. So if you tune at 28hz, you'd be able to play VERY low, since it rolls off half as slow as ported.. However you'd have almost no range on the upper bass notes, since it's rolling off up top and you generally have less cabin gain as you go higher in frequency.

Most 4th orders are tuned closer to 45-50hz for this reason. The slow roll off on the bottom end means they can still play 20-25hz at respectable levels, which the higher tuning still allows 50-60hz bass.

How much space do you have, in inches and what frequency range are you trying to get the subs to play?

That may have been a bit long, so long story short you'll need to get a new box built realistically.

Last edited by T3mpest; 03-07-2016 at 03:15 AM.
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Old 03-07-2016, 07:18 AM
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Quote:
Originally Posted by Maniac View Post
I have 2 sundown x18s could i just use the ported box design sundown provided an just build an sealed part on top to make it 4th order (i think the ported was tuned at 35 i want to be at 28 on ported part) really hoping to learn more about 4ths from you guys


Build the shell to the 4th order
Build sealed side and load woofers in
Run a sweap to find peak... U can adjust the sealed size to change the res freq if needed.
Then tune front chamber to the res freq of your sealed side... Most people shoot for 45-49hz
Good place to start your loading wall is half of cone area and adjust smaller or bigger whatever works for your build.
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Old 03-07-2016, 03:16 PM
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Idk if i want to give up my back seats tho how much louder would it be in a 4th compared to ported
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Old 03-07-2016, 09:20 PM
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Idk if i want to give up my back seats tho how much louder would it be in a 4th compared to ported
As a rough guess, it would take a minimum of 15 ft^3 internal for a 4th to get about as loud as as 10 ft^3 vented. If you can go larger the 4th starts to gain. If you are space-constrained a vented will be louder and probably sound better as well.
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Old 03-09-2016, 07:21 PM
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I appreciate everyones help im going to think about more
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