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Phase alignment on a 15" T-line subwoofer?
Phase alignment on a 15" T-line subwoofer?
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Old 27th October 2020, 01:11 AM   #1
Bluewoldemort is offline Bluewoldemort
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Question Phase alignment on a 15" T-line subwoofer?

I have built a huge choked t-line subwoofer enclosure for a SoundQubed HDX315D2 sub, tuned to around 23hz.

Now this subwoofer is for my car and will stay there, but i thought that this forum might know better about these sorts of "exotic" enclosures.
I mean t-lines aren't rare in car audio, but I can't find that much info either. Especially with a 15" sub.

Now the sub barely fits into my car scraping all four corners of the box, taking almost all the depth also. It's about 80*70*40cm.

The sub and the rounded slot-port are on the same wall, as I've heard this is best for sound quality and SPL. Now the results are lackluster, playing with 3000+ watts it sounds quieter than with the first enclosure that was sub upwards. With about 1000 Watts.

The subwoofer peaks at 17hz, doors closed, so it plays the lows now, but it doesn't do well on the higher notes.

Now I have tried with the sub facing backwards and to the side. I still have to try forward facing, but I don't have big hopes for that.

My next thought is to put the sub firing upwards, because that seemed to work well with the last box, even though it wasn't braced at all or anything.

I'd have to cut a hole in my rear shelf and drop the sub in. (Sub weighs 25kg and the box is 50kg) But the added hole would bring more bass to the cabin anyway, and i could then maybe reverse the sub and have it magnet upwards.

Now I am wondering, don't t-lines rely on the phase-relation of the port and the sub for added low-end? If so, how can i phase-align the sub pointing upwards? I have seen it done with great results, but I just need to know how.


Tl;dr: I'm swapping the subwoofer from the same wall as the port, to another wall. How do I phase-align them?

Last edited by Bluewoldemort; 27th October 2020 at 01:14 AM.
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Old 27th October 2020, 06:33 AM   #2
GM is offline GM  United States
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Can't really comment about why it's poor performing with so little information, but normally with phasing you want the driver, vent positioned such that the acoustic distance from each has the same path length to the listening position, so don't see how it can be done in a typical vehicle.

In a hatchback, it can be folded to place the vent next to the driver with the driver offset at 1/3 [IIRC, been decades since I last did it], but usually there goes much of its grocery, etc., carrying capability unless a big family size one.

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Old 27th October 2020, 10:22 AM   #3
Bluewoldemort is offline Bluewoldemort
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Click the image to open in full size.

The thought of putting groceries in the back is gone.

Here is one very similar to mine, except with two 12" pointing upwards in a hatchback.

Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.

This one doesn't seem to have the same distance to the listener of the sub and port.
But I have heard some say that ported enclosures play louder with the sub and port on different walls. Because the port sound would be in a different phase compared to the sub being on the same wall.

But would it not be enough if the sub is 360 degrees out of phase, thus being in phase again? Sorry if its a dumb question.
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Old 27th October 2020, 11:05 AM   #4
Bluewoldemort is offline Bluewoldemort
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Oh and I measured the sub when it was facing backwards:
IMG-20201008-WA0011.jpg - Google Drive

The violet line is the sub placed on top of a plank of birch plywood, because the original floor folded on itself.

The blue-green line is after I dampened the trunk pretty well and blocked the air vents on the side. That would increase the low end as seen. Then I also built a floor out of spruce plywood because it was cheap. It was too flimsy but I reinforced it with a lot of birch. I'm not sure if that affected the higher bass.

Don't worry about he huge dip after the bass, I only had in 5" mids at the time. Now I have 10" PA mids.

Oh and the sub was on a 10hz hipassfilter set on the amp and a 125hz lowpassfilter from the stereo.

Last edited by Bluewoldemort; 27th October 2020 at 11:08 AM.
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Old 27th October 2020, 12:05 PM   #5
Booger weldz is offline Booger weldz  United States
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You have a Void. offset the driver .
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Old 27th October 2020, 12:22 PM   #6
Bluewoldemort is offline Bluewoldemort
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Sorry, but how? Practically.
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Old 27th October 2020, 12:28 PM   #7
Bluewoldemort is offline Bluewoldemort
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My enclosure looks like the other one i posted, inside. It's choked to give more SPL and power handling, as I have 59 volts @ 1ohm.

IIRC, it was planned not to play much higher than 70hz, because of the low tuning and the chamber. I don't know if I can offset it without removing the chamber.
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