Box For 2x12" Type S

[sweefu]

Hey all,
Helping timboy knock up a box for a pair of alpine type S 12" subs..
They will be getting 500wrms at 2ohm, subs are rated at 300wrms each so its not toooo bad.

I'm just going off the alpine website here, the box will be 3.2cubic foot interal volume, just a normal rectangular prism shape.

Its ported, which i'm not too good at (i always make sealed boxes) But i was going to make the port with 90mm storm water pipe, so was going to make the port about 3.3inches long at about 45hz?
Sorry if this is way off, i'm using this website Subwoofer Enclosure Calculators, Fraction to Decimal, Parallel, Series, Port Length and Volume Calculators

So, quick over view. 2x12" alpine type S in a 3.2cubic foot ported box with a 4x4x3.3 inch port?

Thanks.

[holdenboy]

I'd be going with more port area (bigger) than that. With the little amount of power i think 2 x 90mm ports is more ideal. Your port tuning is way to high also, remember the box will actually peak 7-10hz higher when its in the car, so a "real world" peak of 52-55hz is more like a SPL box, and will sound crap with music.
These two reasons are why your port depth is so short. A good rule of thumb is to get your tuning freq. around 35-40hz and your port area sufficent to get a port depth of about 25-30cm. You will notice a few things from an online calculator, the larger the port/s the longer they need to be to get the desired tuning frequency. Also the lower the tuning frequency the longer the port needs to be, and vise-versa.

I personally dont use online calculators that much, because they dont take into consideration the cabin gain of the vehicle, not to mention loading etc. But if i do use one, this version seems to be very good, even though you need to convert cm to inches. (to get to the box calculator, scroll down the left hand menu until you get to "Basic Enclosure Calculations" near the bottom.

[sweefu]

Thanks for the help mate, i re did some calculations and came up with this:

30x16x16" box = internal volume of 3.28cubic foot

2x90mm round ports each 6.5inches long?

[StoneX]

Those subs suit sealed boxes better than ported and it'd be a hell of a lot easier to design.

[holdenboy]

What wood thickness? I'd be making it out of 25mm minimum. 32mm (2 x 16mm sheets) is ideal.
Say its 25mm, youve got a total box volume of 3.17 cu.ft. Before subwoofer and port displacement (say 0.3-0.4 cu.ft.) so thats an internal volume of approx. 2.82 cu.ft.
2 x 90mm ports tuned to 35hz need to be 11.5" (29.2cm). A 38hz tuning will need a 9.3" (23.6cm) depth.

So it goes back to what i said initially, if you have the right port area you'll require around 12" / 30cm of port depth to get a decent tune.

I would make the box abit bigger though, considering the amount of power they will be fed. Maybe try around 4 cu.ft.?

[sweefu]

Thanks mate,

So back to the drawing board.. 4cu.ft internal or external ?

The 3.2 i gave was internal, after considering the displacement of the subs etc..

Also Just to verify, i want two ports each 11.5" or the two ports should equal 11.5" in total?

Thanks again for all the help.


Wood thickness will be at minimum 16mm

[holdenboy]

Well if youre going to use 16mm, atleast make the baffle 32mm

So yeah, with 16mm wood thickness you get 3.6 cu.ft. Take out the port and sub displacement and you do get around 3.2 cu.ft. Which means a 35hz tune would need a port depth of 24.5cm (24-25 is close enough). BTW that means each port needs to be that long

As you can see the wood thickness makes a big difference on the internal volume. But you do sacrifice output as the box flexes. It wont be a huge issue because of the power youre feeding them but i'd still make the baffle 32mm.

Those measurements were external i assume?

[sweefu]

Okay i'm getting this now haha. We'll be getting the thickest mdf for the money we have haha. The measurements i were giving were internal.

I'm interested to see how this turns out . Will the ports sound best facing the same way that the subs are firing?

[holdenboy]

Oh, so the 30" x 16" x 16" is internal? Well that makes it bigger again! (means a shorter port depth, so go with around 22-23cm).

Yes keep the ports on the same side as the subs. Hopefully youre planning on firing them towards the rear of the car?

Will sound OK, IMO it'll give him more output over sealed.

[sweefu]

Yep will be firing towards rear of the boot in a vr sedan.
These subs used to be in a 1.2cu.ft sealed box (overall volume, not internal! :S

So now will hopefully sound much better.

[holdenboy]

1.2 cu.ft. each, or total? If its total then thats WAY too small for them, 1.0 cu.ft. each is better for sealed.


Anyway, yeah it'll have alot more output now......if you dont know already im a huge fan of ported boxes

[sweefu]

Haha yeah i had a hunch you liked ported boxes! The old box was 1.2cu.ft total outside volume, for the pair :S

I'll post up tomorrow how we go with the box

Thanks for the help mate.

[ethann]

even though you need to convert cm to inches

I got free cuts at Bunnings because I took the measurements to the guy in inches ahaha.
He was like, 'Your to young to be measuring in inches, I like it though, Gives me a challenge to convert them'. Then I when I asked how much the cuts were he said 'No way your paying for them, This has been fun.'
haha.

[StoneX]

You're sealed box was too small. I don't know why you're looking at ported, Type S subs don't suit ported boxes. Will be louder but definitely won't sound better than the recommended sealed box.

[sweefu]

You're sealed box was too small. I don't know why you're looking at ported, Type S subs don't suit ported boxes. Will be louder but definitely won't sound better than the recommended sealed box.

If they were my subs they would be going in a sealed box, but my mate asked me to help him build a ported box for his subs. I know they would sound better sealed, but my mate wants ported so we're giving it a go.

Cheers mate.

[StoneX]

No probs, just thought you were ignoring my first post

[sweefu]

Haha nah mate not at all. If they were my subs i would never have let them go in a 1.2cu.ft box in the first place either.

[sweefu]

Got started today.
Timber was $27
They cut it for $5
Liquid nails $5
screws $7

We cut a new front for it, because the guy didnt guy the timber correctly at the hardware shop :/.
We have cut the front, the subs fit will, also cut the port holes. Put a terminal block on the back.

Here is a pic of the back/bottom/side together. We put 13 nails in the back and 7in each side.. i think its going to be a decent box.

What do you guys think?

[acarmody]

Gotta be careful with getting shops to cut the wood. I bought a 3m piece of pine for a picture frame, asked Bunnings (where I bought it) to cut it in half, says sure, measures it up, and cuts, one piece 130cm, other 170cm, *sigh*, thankfully still worked, just.

Box looks good. What timber did you get. A piece of 2400x1200x24 MDF costs about $80 at Bunnings up here.

[sweefu]

We only got 16mm thick, due to budget restrictions haha. From magnet mart the 2400x1200x16 was $27 and $5 to cut it up, though should have been discounted due to his shoddy cutting skills :P

[StoneX]

2440x1220x18 is $42 from my local timber place.

[sweefu]

Hey here's a thought .. How do i wire 2 dual 2ohm voive coil subs to 2ohm?

Do i run them in a series??

[sweefu]

Would this be correct?

[acarmody]

Yep that would work.

[sweefu]

Here is how we got on today.. All finished.

Used about 116 screws, a tube of liquid nails, and a tube of gap filler.

All is sealed up really really well.. sounds crazy, shakes the whole car.

Thanks for all the help.. i think another mate wants me to help him make on for a pair of his kenwoods now!