Car sub enclosure for 12" driver

[juxta]

Hey guys I'm finally getting round to starting a project.
I'm going to build a new enclosure for my car, it's a wagon so I have a fair bit of room but I need to be able to fit the shopping in sometimes as well as get it out easily when I need more space.

This is all the info I have on the driver.

fjl-1211 Jonah Lomu Woofer 12"


* Power Handling 1300 Watts 650w rms
* Voice Coil 3" Black Alloy SVCImpedence (per coil) 4 Ohms
* Free Space Resonance (Fs) 28Hz
* Efficiency 89db
* Frequency Response 21Hz to 1.2kHz
* Mounting Diameter (mm) 11.22"/285mm
* Mounting Depth (mm) 6.49"/165mm


FS - 26 hz
QMS - 3.717
Vas - 107.1 l
Xmax - 13mm one way
Qes - .35
Qts - .322
Sens - 89 1-W

Overall Dia - 319mm
Cut Dia - 285mm
Depth - 165mm

I've been told ported box design is a little harder than sealed but will be worth the effort. I think a volume of around 50 inches is the go, although I'm new to winisd and didn't have enough data to fill all the fields.

Does 50 inches sound right?
Is ported the way to go?
Am I able to make a flattish box across the back of the seats or should I fill one side from seat to boot door?
And finally how do I measure port length/width (if ported is the go)as well as find one make one? Plumbers pipe could do it???....

Any thoughts would be great

[chris661]

Hmmm.....
Choosing to go vented or not depends on your taste of bass, particularly in cars. You can get both to do what you want, but getting a vented design to give a smooth in-car response can be difficult
A sealed box, done correctly, will get enough cabin gain to mean it's got a flat response to somewhere very low.
A vented box tries to get a flat response by boosting certain frequencies. The cabin gain will also boost these frequencies, meaning you'll have a bump in overall response, which won't sound nice.
In choosing a box - I'd put it at one side, because the box will be easier to build (no sloping sides). Make sure the driver has enough space around it to move to it's full excursion (assuming you'll push it that far) - you might want to get hold of a grill.

HTH
Chris

[juxta]

Originally Posted by chris661

Hmmm.....

In choosing a box - I'd put it at one side, because the box will be easier to build (no sloping sides). Make sure the driver has enough space around it to move to it's full excursion (assuming you'll push it that far) - you might want to get hold of a grill.

HTH
Chris

Ok thanks Chris, sealed will cut out a bit of work. I used to have this driver in this box, it seemed a little small, and when I pulled the driver out I realized the hole's just been hacked at with a jigsaw. It was probably only made for a 10" driver. I might be able to modify this box in some way, keeping the profile but increasing the volume..

Does anyone have plans for a 12" driver similar to mine?

And I'm not sure what volume I need still, winisd came up 50.9inches with a tuning freq of 32.74hz. Not sure if that's right

I can easily build a square box but I'm keen to check kerfing or something to get a snug fit behind the seat..

Cheers

[chris661]

I see what you mean.
The winISD plot - can you show a screenshot. It sounds like you're still modelling a vented enclosure. Generally speaking, car subwoofers are used in very small boxes, to give maximum power handling. Which amplifier are you planning on using it with?

[juxta]

Originally Posted by chris661

I see what you mean.
The winISD plot - can you show a screenshot. It sounds like you're still modelling a vented enclosure. Generally speaking, car subwoofers are used in very small boxes, to give maximum power handling. Which amplifier are you planning on using it with?

Yeah sorry I was still in vented, the capacity now is 28 inches rather than 50 with qtc of 0.71.

I just use a little Fusion amp, it's only rated at 120w rms I've found out now. 400w max but I've never had it near full power and and it's been rattling everything loose.

Fusion Fusion PP-AM4002 (Discontinued 2007/2008 Model) - Online Car Audio - Bringing the future to you
I've only had this car a little while and I've been putting off installing this for a while, for just the reason that my old car was tight as anything and after 6 months it buzzed like a bee. But now I'm sick of listening to talk radio on the standard stereo ...

These are the only graphs with anything on them, SPL is blank

[juxta]

Here's a better link to the amp, I suppose running mono it would be bridged 240w rms. Not much for the driver but I suppose it's safe, as long as I don't stress the little amp

Fusion PP-AM4002 400W 2 Ch Car Amplifier [PP-AM4002] - $279.00 : Emtech Automotive

Edit: I was in litres to not inches! I thought it was strange only being able to use inches. 28 LITRES volume, I must be going blind

[chris661]

28L is nice and small, and don't worry about the amp - it has reasonable power. Try playing with the crossover when you get it up and running.

SPL will be blank because you either haven't entered the SPL, or it can't calculate it.
How does the excursion graph look? Assuming the graph works, keep adding power until you hit limits (absolute mechanical excursion is somewhere between Xmax and 2x Xmax). If you can put more than say 50W in, you'll be fine. My sub (theoretically) runs out quite early, but it's surprising how loud 90dB actually is.

Good luck
Chris

[head_unit]

I'm confused how you're talking about cabinet volume as 50 or 28 inches...do you mean liters?

I don't have a simulator handy, so can only comment generally.

Sealed boxes have a low frequency rolloff which kinda matches the "cabin gain" of the car. So sealed boxes will end up with a flat response in most cars. A ported box will tend to have a kind of bump, if memory serves. That's not necessarily bad-you want a rising response at the very low end to compensate for road noise.

But to sound good, ported boxes need to be tuned low, like below 30 Hz. And they need a big cross-sectional area to flow a lot of air, or they just choke off at higher volumes (which defeats the purpose of porting in the first place). And both ends of the port need to be clear for a couple of port diameters in all directions again so as not to impede airflow. "Bottom" line (pun intended, sorry!) is that proper ported boxes for the car can be sometimes physically impossible, unless the enclosure is a few cubic feet.

What vehicle do you have? Is the seat porous, or metal-backed? If the seat is very solid, you can't mount the enclosure right up against it. Some cars trunks are so sealed you might have to try and mount a sub inside the passenger compartment, or remove the rear speakers to make a vent. (And who cares about rear speakers unless you have 5.1 anyway?)

[chris661]

Originally Posted by juxta

Edit: I was in litres to not inches! I thought it was strange only being able to use inches. 28 LITRES volume, I must be going blind

Your memory serves you about the frequency response. A bump in response may help with road noise, but might sound worse.

Chris