critical Q for car

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The car version has lower impedance which is appropriate for car amps. It's also slightly more expensive. It has a higher fs and is more efficient. All this translates into more output in a car - you don't need the fs as low as you get more assistance from the cabin gain. For cars, sealed makes sense as the rolloff should be quite close to the cabin gain. I believe the car version is also suited to an even smaller box.

With a vented box you have to make sure it doesn't get boomy due to cabin gain. Space is also a premium so a vented car box can be a lot more tricky since you try to tune fairly low to avoid boominess - probably more like an EBS. In such a small box its difficult to get a decent vent.

Now in a typical flashy looking car audio subwoofer, you don't have much xmax (despite their big surrounds they often have a wimpy 5mm xmax), so its not quite so difficult to get a vent in. But if you get a serious car audio sub like the XLS car version, then it's a bit more of a challenge.

I'd just go with a sealed box.

Have a look at diysubwoofers.org as they have some good info on car subs and cabin gain

Two great things about car subs:

1. no room modes (you are spared probably the biggest hassle with home audio subs)
2. small space means lots of bass with just a small sealed box

A critically damped alignment is a good thing, but infinite baffle is even better. If you can put a sub in a car so that it uses the boot as the box, then do it. If you are feeling clever you could use a second driver and push pull operate them. It means being a little tricky in how they are mounted. In some cases this would be an understatement.

If you must make a box then there are many tutorials on doing with with fibreglass to fit into your car.

Warning!!! - the XLS drivers have an impedance curve that dips low. Your amp must be stable down to 2 ohms for the 4 ohm car version.
 
Xls isnt too spectacular. For car audio get a car audio sub yes. Adire has some pretty good subs that are well priced to say the least. The Tempest and DPL12 are good subs with XBL2 and high Xmax. A DPL12 will have a low Q in even a small box so you can get relitively dampend bass without taking up much room for a big box. You can go ported if you'd like, but sealed does match the ~12db/octave rolloff of cabin gain pretty in most vehicles.
 
Xls isnt too spectacular.

Quite a few, notably including Linkwitz, would disagree.

The Tempest and DPL12 are good subs with XBL2 and high Xmax.

Don't you mean Tumult?

DPL12 with XBL2? Are you sure about that?!!!

DPL12 is designed contrary to the logic normally used for car subs - high fs and higher efficiency. Seems a questionable choice to me. The basket is a nice design if you intend for it to be seen though.
 
Neither of those drivers have XBL^2. Only the following drivers have XBL^2

Adire Koda 8, 10, 12 (15?)
Adire Extremis 6
Adire Sadhara 12
Adire Brahma Series (10, 12, 15, Extreme)
Adire Tumult
CSS SX10
CSS WR125
Resonant Engineering XXX Series

There are some others which aren't commercially available, and others that just aren't commercially available yet, and probably some that I've just plain missed, but the Tempest and the DPL2 still have regular SGLC motors.
 
uhh yeah, your right about the adire subs and xbl2. Apparently I should cut back on the crack smoking. I wouldnt say the XLS is anything spectacular still however. 12.5mm one way excursion, how low can you go? not very. One thing I think myself is that for true reproduction of the low freuquencys we need first, Low Fs. Second, high Xmax and Sd. Im not talking about anything above 40hz, even some midwoofers can go that low, especially in car. Subwoofers either need incredible xmax or incredible Sd. Both together will give you the most LF output. I dont like the idea of a dinky 12 with 12.5mm excursion, no matter how crisp it may sound. When I'm lookin for subs, its all about excursion, cuz thats what really matters for my infrasonic version of that sound. I'll comprimise a bit of SQ but if I can get down to 10hz its worth it. 10hz is easily achieved in car with cabin gain with some good subs and a proper enclosure (sealed preferrably for good music listening and little comprimise on LF extension)
 
Out of curiosity I did a comparison of the XLS-car vs home audio version vs the DPL, all in a 28L sealed box.

The XLS drivers had a low Q in a box this size, 0.6 for the car version & 0.5 for the home version. The DPL wants a bigger box and has a Q of 1 in a box this size. The transient performance is likely to suffer.

Looking at the response, both the XLS car and home audio version are very similar. In fact, it seems the real advantage of the car version is that it has a lower impedance, hence it will make better use of the amps power. The DPL has a slightly sharper rolloff which occurs lower.

Consider that cabin gain will typically be 12db/octave below 60 - 80 Hz. Below 50 Hz the XLS subs rolloff at about 8 - 9 dB/octave. The DPL rolls off below 35 Hz @ about 12db/octave. As a result, the DPL will have a big boost around 40 - 60 Hz. The XLS looks likely to be a better match with cabin gain IMO.

The tiny difference in xmax between the XLS vs the DPL of 1.8mm is nothing to speak of. It amounts to less than 1db!

Of course, if you really did want the DPL, then you can use eq, which is probably a good idea no matter what driver you chose. You change the Q with a Linkwitz transform, but I doubt this would be as good as using a driver that has a lower Q in a small box in the first place.

If the XLS doesn't have enough output for you, then there is always the Brahma!

Here's the chart, with gain applied so that the F3 of each can more easily be seen.

Red - XLS car
Green - XLS
Blue - DPL
 

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