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Discussion Starter #21
The driver doesn't determine the tuning frequency, the box volume and port surface area and length do.
Oh, cool. Good to know. So without knowing the driver T/S, I could still design an 80L enclosure that is tuned to 22-24hz with either a 3" port or a 4" port. Can I use WinISD for this?
 

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Discussion Starter #22
In WinISD, I got a 90L enclosure with TWO 3" ports @ 22" long = a tuning of 22hz. Does that sound right? I am going to make 2 endcaps. One with a 22hz tuning and one with a longer port (15") for a 24hz tuning and see which one sounds better in the real world.

Am I seeing the numbers correctly?
 

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Discussion Starter #23
Remeasured the original cabinet and port. Inside dimensions of the cabinet is 14 x 14 x 10" (~1900 in^3). The port is a slot-pot design and its 12 inches long, 5 inches wide and 1.75 inches tall.
 

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That means it's a 1 cu.ft. box tuned to 40 hz. Now we can guesstimate the amp has a hi-pass filter around 40 hz or so. If you put the sub in a bigger cabinet there's no sense tuning any lower since the amp is blocking the frequencies below 40 hz. If you do put the sub in a bigger box and tune it to 40 hz, the sub will bottom out since it takes less power to reach Xmax in a bigger cabinet. This should tell you the sub, amp, cabinet size and tuning were all designed to work together for this specific application. I strongly suggest you put the sub and amp back in the original cabinet. If you do decide to pursue this let us know how it turns out.
 

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Discussion Starter #25
That means it's a 1 cu.ft. box tuned to 40 hz. Now we can guesstimate the amp has a hi-pass filter around 40 hz or so. If you put the sub in a bigger cabinet there's no sense tuning any lower since the amp is blocking the frequencies below 40 hz. If you do put the sub in a bigger box and tune it to 40 hz, the sub will bottom out since it takes less power to reach Xmax in a bigger cabinet. This should tell you the sub, amp, cabinet size and tuning were all designed to work together for this specific application. I strongly suggest you put the sub and amp back in the original cabinet. If you do decide to pursue this let us know how it turns out.
I think I am still going to try it. At the very worst, it will suck and I can just swap out the endcap for one that fits an SDX10 or something.

Should be able to start cutting this weekend!
 

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Discussion Starter #26
Just wondering if my numbers are correct. If I have an 80L enclosure (4882 in^3) and I wanted a 24hz tune with a 3" PVC pipe, that pipe would be 15" long, right? Just want to make sure befor I cut...
 

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Discussion Starter #27
Just wondering if my numbers are correct. If I have an 80L enclosure (4882 in^3) and I wanted a 24hz tune with a 3" PVC pipe, that pipe would be 15" long, right? Just want to make sure befor I cut...
Hoping these cabinet calculations are right?

One more question; if the amp indeed has an active high-pass filter, can I play test tones from 60hz down to 20hz or whatever in 1-2hz increments and determine the high-pass cutoff when there ceases to be a sound played?
 

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I'm at work, I'll check your calculation when I get a chance. The filter isn't a brick wall, the SPL will drop so many db's per octave depending on what "order" the filter is. A second order filter will drop 6 db per octave, a third will drop 9 db's, a forth will drop 12 db's.
 

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Discussion Starter #29
I'm at work, I'll check your calculation when I get a chance. The filter isn't a brick wall, the SPL will drop so many db's per octave depending on what "order" the filter is. A second order filter will drop 6 db per octave, a third will drop 9 db's, a forth will drop 12 db's.
Can EQ then defeat a HP filter by boosting the lower frequencies? Obviously nobody with that kind of equalizer would be running a budget build like this, but I was just curious.

Thanks Mike! I start cutting tomorrow. Right now its an 80L build with a 21" ong 4" PVC port! :)
 

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Discussion Starter #31
You can only boost if you have the power and the sub has the excursion capabilities. A 6 db boost takes 4 times the amount of power. If you send 150 watts to a sub and a frequency is boosted 6 db, that frequency would require 600 watts.
Yeah, I'd never attempt that with this build, just curious. Good to know though.
 
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