Help with 4th order box for 4 JL Audio

[jessdabest77]

I have a O1 Silverado crew cab and want to build a blowthrough with four JL Audio W6v2 12's. Hoping someone might give me size for it,sealed, the ported, port area and what it should be tuned to. It'll be ran on 2-3K amp power, thanks in advance.

[Triticum Agricolam]

Those subs should work well in a 4th order bandpass.

JL recommends 1.25 cu ft per sub for sealed usage. That would be a good starting point for a bandpass box as well. I'd be careful with the power if you are going to be putting much more than 500 watts a piece to them though. Excursion could get a bit high below 30 Hz. Proper use of a subsonic filter could be beneficial.

Front chamber size depends on how much bandwidth your want. Smaller front chamber = larger bandwidth but lower efficiency, larger front chamber = smaller bandwidth but higher efficiency. Somewhere in the range of 4-8 cu ft would be reasonable. Port size will depend on how big you make your front chamber. For front chamber tuning 45 hz is a good starting point.

[frogcase2002]

Those subs should work well in a 4th order bandpass.

JL recommends 1.25 cu ft per sub for sealed usage. That would be a good starting point for a bandpass box as well. I'd be careful with the power if you are going to be putting much more than 500 watts a piece to them though. Excursion could get a bit high below 30 Hz. Proper use of a subsonic filter could be beneficial.

Front chamber size depends on how much bandwidth your want. Smaller front chamber = larger bandwidth but lower efficiency, larger front chamber = smaller bandwidth but higher efficiency. Somewhere in the range of 4-8 cu ft would be reasonable. Port size will depend on how big you make your front chamber. For front chamber tuning 45 hz is a good starting point.

Wont the port area be dependent on the subs , not the size of the enclosure? . . I know length will but not area

[jessdabest77]

So 1.25 cf sealed per sub what about ported side? What would the box be in total and how big of a port? I'll put two Fosgate 1000's in instead for power. Thanks again

[Triticum Agricolam]

Wont the port area be dependent on the subs , not the size of the enclosure? . . I know length will but not area

A lot of things affect how much port area you need. Chamber size, input power, tuning frequency, and size/specs of the subs. The size/specs of the subs make less of the difference than you might think.

Since in the OPs case we know what the input power, tuning frequency and subs will be the main variable is the chamber size.

[Triticum Agricolam]

So 1.25 cf sealed per sub what about ported side? What would the box be in total and how big of a port? I'll put two Fosgate 1000's in instead for power. Thanks again

Like I said, front chamber size depends on how much bandwidth you want. Smaller front chamber = larger bandwidth but lower efficiency, larger front chamber = smaller bandwidth but higher efficiency. Everything is a trade off. Somewhere in the range of 4-8 cu ft total for the front chamber would be reasonable. There isn't one right answer, it depends on what you goals are. Port size will depend on how big you make your front chamber. With a 8 cu ft front chamber on 2000 watts I'd suggest no less than 120 sq in of port. With a 4 cu ft front chamber I'd suggest no less than 80 sq in. If you go somewhere in between 4 and 8 cu ft your port will need to be somewhere between 80 and 120 sq in.

[jessdabest77]

Wow,thank you,good info there.I'll try staying between the 4-8 cf front camber.Another question,since the truck is a crew cab,would the fourth be louder than if I did just two subs in a ported box still a blowthrough?

[Triticum Agricolam]

Wow,thank you,good info there.I'll try staying between the 4-8 cf front camber.Another question,since the truck is a crew cab,would the fourth be louder than if I did just two subs in a ported box still a blowthrough?

It depends, if you make the front chamber large, they will probably be equally loud, but the ported box will have wider bandwidth, and will take up a lot less space. The hard part would be how to implement it as a blowthrough.

[Triticum Agricolam]

Here is a graph comparing a 8 cu ft ported box to a 4th order bandpass with three different front chamber sizes:

The green line is the ported box.

The yellow line is 5 cu ft sealed, 4 cu ft ported.

The blue line is 5 cu ft sealed, 6 cu ft ported.

The red lie is 5 cu ft sealed, 8 cu ft ported.

The middle bandpass box has nearly identical performance to ported box up to about 55 hz, above that the ported box can play as high as you want, but the bandpass box rolls off.

The large bandpass box has more output than the ported box, but only between 35 to about 57 hz, which is a pretty small frequency range, much less than an octave.

The small bandpass box has a pretty large bandwidth. Its upper and lower F3 points are about 75 hz and 28 hz, but it gives up around 3 db compared to the ported box and middle bandpass, and almost 5 db compared to the large bandpass. For comparison the large bandpass box's F3 points are about 60 hz and 35 hz.

As I said before, there isn't a single right answer for box specs. What's going to be best for you depends on how low you want to be able to play, how high you want to crossover to your mids at, how flat of frequency response you want, etc. Cabin gain is going to significantly change the frequency response you are going to get in the vehicle of all of those boxes compared to what's shown in the graph. Its going to boost the low end output a lot and shift the f3 points down quite a bit. Whatever you do, I'd suggest making the port adjustable so you can tweek the tuning once you get the box playing, you may want to raise the tuning some to get more upper end output.

Assuming you want to cross over to your mids around 70 hz or so, if it were me I'd probably go for the 6 cu ft front chamber size. Its a fair compromise between bandwidth and efficiency.

[jessdabest77]

great,I'll try the fourth order and i'll post pic's and hopefully a vid of it.