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Old 2nd August 2011, 09:02 AM   #1
Hayden is offline Hayden  Australia
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Default would this sub box work?

just wondering if done right will this box work or does the 12inch subwoofers need to be the same phase?

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Old 2nd August 2011, 10:43 AM   #2
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The idea of that system is for both drivers to operate the same port, by pressurising the chamber.

If the drivers move as indicated, you'll get no output.
They should be wired in phase.
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Old 2nd August 2011, 12:12 PM   #3
Hayden is offline Hayden  Australia
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Thought so, I was talking to a car audio expert that has been installing and making sub boxes for years and years; he said it's not realy the subs making the sound it's the port. I'm confused if the subs are out of phase with my knowlage they will cancel each other producing low output. I am no expert at building boxes and I'm not saying he is wrong but I can't see how this box would work.
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Old 2nd August 2011, 01:33 PM   #4
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With the arrows depicting cone movement as shown, then no, it won't work. You are quite correct.

Reverse one of the arrows, and it will work fine.
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Old 2nd August 2011, 03:23 PM   #5
Hayden is offline Hayden  Australia
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He was extremely determined that it would work. I guess even an expert can be wrong.
Thanks for clearing it up.

If other members have any input you are welcome to post :-)
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Old 2nd August 2011, 04:12 PM   #6
nad is offline nad  United Kingdom
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Your expert is wrong.


Does he know speakers create 'sounds' by moving air?

When it comes to ported enclosures such as your drawing, it's the displacement of air INSIDE the box through the port that gives the 'sound', no displacement, no sound.

If you look at the diagram below, figure A (the pink bit) has a volume of say 10 litres, now look at figure B with the drivers out of phase, the displacement of air caused by the driver on the left is simply allowed to fill the recess caused by the driver on the right moving to the right. There's still 10 litres of air in there (no displacement).

Figure C shows 'in phase' drivers, the 10 litre volume inside the box (pink) is displaced by both drivers forcing the air through the port creating a mass rush of air...... = boom.


Simple as that.


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Old 2nd August 2011, 06:44 PM   #7
Boscoe is offline Boscoe  United Kingdom
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I don't quite understand where the radiation comes from in these types of enclosures?
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Old 2nd August 2011, 09:12 PM   #8
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Radiation ??

edit: oh,

the air in the port acts as a resonator, the air in the port is not excursion limited so it can be very loud and the confined space inside the box acts to limit the cone excursion much like a BR box once the port has coupled to the driver limiting driver excursion.

actually you could think of it as a ported box with no front wave.

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Old 2nd August 2011, 09:17 PM   #9
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The port is the only coupling to the outside, so all the output propagates from there. It's effectively a dual-driver 4th order bandpass, but each driver has its own volume of air to sit in, rather than sharing with its twin.

(As a thought, could effectively blowing air across the port give some form of warbling output, like blowing across a bottle lots of times a second?)
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Old 3rd August 2011, 07:13 AM   #10
Boscoe is offline Boscoe  United Kingdom
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If that's the case does it sound as good as a regular ported box?
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