Ported Box for Exile BIG 12 MKII

[Cdoogles]

Hey folks,

I'm getting ready to build a box in my Axis T23 for the new Exile 12" sub. Looking at Exile's website the only info I have is that it requires a 1.7" cu ft ported box. I can fit a ported box of that size under the helm on the driver's side without too much trouble but I'm not sure where to get the rest of the specs for the sub to build the box. Anyone else dug up this info yet or built a box for this sub?

Thanks!

[David]

The norm is for the number to describe the internal net chamber without port or port wall displacement. In that case, 1.7 would end up being a large enclosure unless the port dimensions were very small. I wouldn't assume anything until you get it verified directly from the manufacturer, or get the full Thiele/Small parameters and design your own enclosure. It's good to model the enclosure anyway and know what type of behaviors you can expect....before you go building a box. It's also good to know what those specs are before you select any particular woofer. Is it suited for bass-reflex in the first place? All things you should absolutely know.

[Cdoogles]

Thanks David. I totally agree with everything you said. I guess what I was poking at was if anyone had got the Thiele parameters for the MKII sub yet. I can try to chase down Brian with Exile and see if he has them but I couldn't find them on the web.

Thanks!

[IXFE]

Hey folks,

I'm getting ready to build a box in my Axis T23 for the new Exile 12" sub. Looking at Exile's website the only info I have is that it requires a 1.7" cu ft ported box. I can fit a ported box of that size under the helm on the driver's side without too much trouble but I'm not sure where to get the rest of the specs for the sub to build the box. Anyone else dug up this info yet or built a box for this sub?

Thanks!

Here's the specs I got from Exile. For my Big12, my box will be 2.0 cu. ft.

[David]

You really need to get the entire Thiele/Small parameters and design your own enclosure according to the behaviors you are wanting.

For example, I would not recommend a 3-inch round diameter port on a 12-inch subwoofer, any 12-inch sub. The port function will compress at high volumes and you are inviting port noise. Even a 4-inch round port on some 12-inch subs will be too much velocity through that size of port. A port surface area of about 20 sq. in. is a good target for a high Xmax 12-inch sub which is going to mean a much longer port to tune at the same frequency. Before you leap learn more about this.

[Cdoogles]

Here's the specs I got from Exile. For my Big12, my box will be 2.0 cu. ft.

Thanks IXFE! Exactly what I was looking for!

[IXFE]

You really need to get the entire Thiele/Small parameters and design your own enclosure according to the behaviors you are wanting.

For example, I would not recommend a 3-inch round diameter port on a 12-inch subwoofer, any 12-inch sub. The port function will compress at high volumes and you are inviting port noise. Even a 4-inch round port on some 12-inch subs will be too much velocity through that size of port. A port surface area of about 20 sq. in. is a good target for a high Xmax 12-inch sub which is going to mean a much longer port to tune at the same frequency. Before you leap learn more about this.

I am also building a box for my new Big 12. So that makes two of us now.

I'm building my box out of 1" MDF with a 1.5" baffle. The inside volume is 2.0 cu ft, as stated above. I was going off the "Normal" spec on that chart I posted. See pics below for the mock up I did out of 1" and 1.5" styrofoam.

I have never built a box on my own before, but the 3" port set to 10" of length did surprise me too. I didn't really understand what you said in your post above. Can you just tell me what you think is the right diameter and length for my port?

Edited March 27, 2015 by IXFE

[David]

IXFE,

You can plug the T/S parameters into any number of bass box programs that will model the enclosure and port for you. But you first have to get the T/S parameters from the manufacturer.

It's easy to deduce that a given port is way to long so you simply reduce the surface area to shorten the port. That is what the graph has done. But it's not that simple. You do not want to turn your sub box port into a trumpet. A common term for port noise is 'chuffing'.

Also, the woofer/box/port behavior is very different at 100 watts than it is at 1 watt. So if the measurements are done at 1 watt, they're incorrect.

Consider this simple illustration. Let's say you have a woofer with a radiating surface area of 81 sq.in. Now you are trying to push a similar force through a 3" port with a surface area of 7" or through a 4" port with a surface area of 12.5". Now the velocity of air moving through the port must increase in order to displace a similar amount of air. Because the box and port are functioning as a tuned resonator, the force coming through the port is actually far greater than that created by the woofer.

So when the air speed thru the port exceeds a certain percentage of the speed of sound, or exceeds a certain number of feet per second, the port function changes, it compresses, and becomes less efficient. And you also get a nasty byproduct of noise.

So based on this, above I recommended a port surface area of around 20 sq. in. for a 12-inch sub. The specific length will create a resistance that combined with the box compliance will create that resonation at a particular frequency. If you change the surface area you must also change the length, with the inverse also true, to tune at the same frequency.

From there you will select the length in order to select the tuning frequency. Longer/lower for deeper extension. Shorter/higher for more peak output. You may be going for max SQ with a wide linear response and minimal ripple. You may be going for max SPL over a narrower bandwidth with little regard for the rest. You have that latitude.

But you need to get the Thiele/Small parameters to do it right.

[shawndoggy]

IXFE,

You can kindof reverse engineer the box. Assuming the numbers you posted above (2.0 ft3 / 10" port) are gross (meaning that the 2.0 ft3 is BEFORE displacement of the sub inside the box and BEFORE displacement of the port inside the box), then you could assume that the NET of the box is about 1.85 (.1 for sub .05 for port). So then you can figure out that a 1.85 ft3 box with a 10" port is tuned to approximately 29hz. Then you can figure out what a 4" port length would need to be to get a similar tune in a similarly sized box. The 4" port needs to be almost twice as long (approx 18.5"), but then you also need to remember that a 4" x 18" port is going to displace much more (about 3x more) inside the box, which reduces your NET box to about 1.7, which in turn requires a slightly longer port still to maintain the same tuning frequency (about 20").

You can play with the variables here:

port length calculator

http://www.mobileinformationlabs.com/HowTo-1Woofer-Box-CAL%20Port%20lenth%201.htm

volume of a cylinder calculator (for calculating port displacement)

https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=volume+of+a+cyllinder+

Edited March 27, 2015 by shawndoggy

[shawndoggy]

Remember though it really is important to know whether the numbers in the graph you shared are net or gross. If they are net, then you actually need a 2.1+ box to get to the 2.0 spec'd.

[IXFE]

Remember though it really is important to know whether the numbers in the graph you shared are net or gross. If they are net, then you actually need a 2.1+ box to get to the 2.0 spec'd.

I was told those numbers are "gross" meaning I'm good with my 2.0 cu ft box.

[IXFE]

How does one know what frequency to aim for? You said 29hz... is that some magic number?

Whenever I see prefab enclosures they seem to be tuned in the mid 30's.

I kind of knew I shoulda hired this project out.. [emoji15]

Edited March 27, 2015 by IXFE

[shawndoggy]

How does one know what frequency to aim for? You said 29htz... is that some magic number?

The best way to know is to get the T/S parameters and model how the sub will perform in a box with a free program like winisd. That's what David was trying to say.

But we don't have the T/S Parameters, so I'm just going under the assumption that the tuning frequency of the 2.0 box is "right". I just reverse engineered the box using the port length calculator and figured out that when a 1.85 net box is tuned to 29hz a 3" port is about 10" long.

So the magic I'm assuming is that the factory's 29Hz recommendation is right. Once you know 29hz, you can roughly model other port area configs. But you won't get a true prediction of how the sub will perform without modeling (which again requires the T/S parameters that come with pretty much any other sub on the market).

Edited March 27, 2015 by shawndoggy

[IXFE]

The best way to know is to get the T/S parameters and model how the sub will perform in a box with a free program like winisd. That's what David was trying to say.

But we don't have the T/S Parameters, so I'm just going under the assumption that the tuning frequency of the 2.0 box is "right". I just reverse engineered the box using the port length calculator and figured out that when a 1.85 net box is tuned to 29hz a 3" port is about 10" long.

So the magic I'm assuming is that the factory's 29Hz recommendation is right. Once you know 29hz, you can roughly model other port area configs. But you won't get a true prediction of how the sub will perform without modeling (which again requires the T/S parameters that come with pretty much any other sub on the market).

Shawn, still not seeing where you got 29hz as a factory spec. It's not specified in the chart or on the web site.

[shawndoggy]

IXFE -- the box. A net 1.85 box with a 10" long 3" diameter port is a 29hz box. It is a 29hz box with a 10" sub or a 15" sub. It is a 29hz box with an exile sub or a wetsounds sub. It just "is." Run the numbers in the port length calculator I provided above if'n you don't believe me.

Edited March 27, 2015 by shawndoggy

[David]

Shawn is just helping you to convert the port. That's good info. But I would prefer to start with the horse rather than the cart. At this point I wouldn't take anything for granted. No crap shooting.

You can look at the port and box as interdependent and independent of the woofer but only once you have established a base box size which IS related to the particular woofer.

You can tune any size box to any frequency but that won't give you consistent and good sounding results.

You're not going to use the identical box size for every 12-inch woofer, whether high 'Q' & high Fs vs. low 'Q' & low Fs. First, you have to find out if you have a woofer with the right parameters to even be suitable for a ported enclosure.

29 Hz would be an unusually low tuning frequency, even for an SQ alignment, and particularly in a boat. You certainly don't want to tune the port below the woofer Fs. And you don't know yet what the Fs is.

If you have to modify the box displacement a bit to get everything to fit, that will alter the port displacement.

A change in port and port wall displacement combined with the internal cavity net displacement will alter the external displacement, which matters when you are trying to fit it in a boat.

It gets sloppy.

So back to the horse before the cart. Start with a complete set of Thiele/Small parameters. Make this thing accurate and easy.

[IXFE]

Thanks guys for helping me.

Shawn, I do believe you. Totally not trying to be difficult... I just don't speak your language.

David, you last post is particularly helpful... sometimes you never know what combination of words it will take to penetrate my thick skull.

Btw... this might be helpful. I got both from Exile an hour ago (specs for the Big 12). I guess it's so new they are just now updating the web site.

They also told me 4" port, 15" in length, as opposed to that first chart I posted. I'm gonna try the software you referenced (once I get to a pc).

I think this reads 38hz is ideal...?

Edited March 27, 2015 by IXFE

[Cory]

I'm SO happy I went with a sealed enclosure... My head hurts just scanning these posts...

Edited March 27, 2015 by Cory

[shawndoggy]

I'm SO happy I went with a sealed enclosure...

ha!

I've run my two subs back to back in my truck for the past couple weeks. The JBL w12GTi in 1.1 sealed (was in my MB last season), and the arc audio flatline in the 2.0 ported that is in my stereo thread.

I have to say that I really prefer the ported config. It goes Loooooooooow, but is also still really responsive with regular music. I'm very happy with how it turned out. So happy that I want to build a ported box for the JBL sub to see if I can get a similar bump in that bottom end output. As it stands the JBL probably has a slight advantage over the flatline on a rock kick drum (think The Cult or AC/DC). But on most current top 40 stuff, the flatline just destroys it on the same power (hd 750/1).

Edited March 27, 2015 by shawndoggy

[Cory]

ha!

I've run my two subs back to back in my truck for the past couple weeks. The JBL w12GTi in 1.1 sealed (was in my MB last season), and the arc audio flatline in the 2.0 ported that is in my stereo thread.

I have to say that I really prefer the ported config. It goes Loooooooooow, but is also still really responsive with regular music. I'm very happy with how it turned out. So happy that I want to build a ported box for the JBL sub to see if I can get a similar bump in that bottom end output. As it stands the JBL probably has a slight advantage over the flatline on a rock kick drum (think The Cult or AC/DC). But on most current top 40 stuff, the flatline just destroys it on the same power (hd 750/1).

Wild Flower!!!

Edited March 27, 2015 by Cory

[shawndoggy]

Wild Flower!!!

haha peace dog is always on my sub test list.

[Brianinpdx]

Holy smokes.. I missed all the hooopla. Sorry gents, I was spring breaking with some youngsters.

The enclosure graph I see IXFE posted came from my Electrical Engineer at Exile. You should be very tuned very well and have plenty of power to make your woofer sing. I believe they are updating the product page on the website with the owners manual for download. Anyone have a question on Big 12, shoot me a PM. Happy to answer.

-Brian

I won't even try to debate the Sealed versus Ported enclosure design. Everyone is right, and everyone is wrong. Just depends upon your point of view. Scientific enough? Guys ask me daily what they should do, and my personal point of view is-- if you have an amplifier with built in subsonic filtering (to filter out the freqs below port tuning), and enough available space under the helm, &&& wood working skills - then ported all the way in the open air environment of boat stereo. If you don't have one of those area's covered, then do a sealed enclosure and make sure you have plenty of power on the subwoofer because it'll need every bit of output you can extract. Under powering in the boating environment is not a good thing. In the auto world, I'd say sealed every time and forget ported.

Edited March 28, 2015 by Brianinpdx

[IXFE]

Holy smokes.. I missed all the hooopla. Sorry gents, I was spring breaking with some youngsters.

The enclosure graph I see IXFE posted came from my Electrical Engineer at Exile. You should be very tuned very well and have plenty of power to make your woofer sing. I believe they are updating the product page on the website with the owners manual for download. Anyone have a question on Big 12, shoot me a PM. Happy to answer.

-Brian

I won't even try to debate the Sealed versus Ported enclosure design. Everyone is right, and everyone is wrong. Just depends upon your point of view. Scientific enough? Guys ask me daily what they should do, and my personal point of view is-- if you have an amplifier with built in subsonic filtering (to filter out the freqs below port tuning), and enough available space under the helm, &&& wood working skills - then ported all the way in the open air environment of boat stereo. If you don't have one of those area's covered, then do a sealed enclosure and make sure you have plenty of power on the subwoofer because it'll need every bit of output you can extract. Under powering in the boating environment is not a good thing. In the auto world, I'd say sealed every time and forget ported.

Woodworking skills...?

Damn! I knew I was missing something from that list!!

[Brianinpdx]

IXFE - if the Intel thing doesn't work out, well, you can become a pro installer.

[Fman]

I'm SO happy I went with a sealed enclosure... My head hurts just scanning these posts...

Same here, keep it simple...way too many brain cells being used here.

My last three boats have had sealed boxes, never thought to myself I was lacking bass in the boat. Maybe I need to experience a vented box to see the difference or I just have low standards.

Edited March 28, 2015 by Fman