Help with Brahma 15" box.

[Vageta31 10+ year member]

Well I finally took the plunge and ordered a 15" Brahma today. It was a close race between it and the XXX but since XXX's are backordered for at least 2 weeks it made my decision simple. The main reason I considered the XXX was because I own an Xterra and I thought the theme matching would be cool.

At any rate I'm currently designing my box and need some assistance. I am going to run it ported and tuned pretty low. I believe the recommended enclosure is 3-3.5 cubes tuned to 30hz. I definately don't want to go any bigger than this and may even favor the smaller 3.0. I know for a fact Dan Wiggins says the Brahma is NOT a big box woofer and can work in less then 3. I will be running a Tsunami 1100db to it so I don't want to go too big and risk being able to damage the speaker which is why I'm thinking 3 cubes tuned to 30hz might be safer.

So the main problem lies in the fact that even though my Xterra is an SUV, the cargo area is kind of cramped. Due to stadium seating and an overall high floor I don't have much height to work with because I want the box to fit under the factory cargo cover when I'm not in my car. In fact it's so shallow that firing the Brahma backwards is not an option because the dia. is like 15.5" and the bottom of the cargo cover retractible bar is about 14". So I'm looking to do an up firing design which may give me more bass anyways and reduce the risk of something in the trunk damaging the woofer.

Basically what I'm working with is external dimensions of 42" wide(between wheel wells), 13" high and then as shallow as possible to save trunk space. I think the trunk is about 32" or so from trunk lid to seat so if I could do half of that I'd be happy. So 42x13x16 external is my rough guidelines though I'd be willing to extend it another inch or 2 if needbe. I also plan on doubling up the baffle for extra stability and to recess the Brahma so I have a built-in 3/4" gap to make it easier to fabricate a grill. Adire says give 2" clearance to grill. Also because of the high floor I won't gain much space by using the slope of the seat. I plan on using this small area to mount the amps with a little breathing room. I figure if I mount them on the bottom of the box behind the seat they'll be out of view and still be able to breath.

So can somone help with the numbers on getting a box in that space or shallower if possible while tuning to 30hz with a slot port? Also if I aim the woofer up and the port(s) backwards will that cause a problem? I want to install the woofer in the middle of the box so I may do 1 slot port on each side to make it easier and more uniform looking.

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[Trixter 10+ year member]

Using the dimensions you gave: 42 x 13 x 16, you get 40.5 x 11.5 x 14.5 internal. (This does not include the extra baffle you want to add.)

Using these numbers you get 3.91cu' enclosure. The displacement for a B-15 is .25cu'. This leaves you with .66cu' to play with for port displacement. If you have two slot ports 7.75"(H) x 2"(W) x 28.5"(L) on each side of the box facing up, this adds up to .61cu'...wich in turn gives you a total of 3.05cu' of air space. This is tuned to 30Hz. (The port length I gave includes the port end correction factor...assumming you will be using an outside wall of the box as a side of your port.) You need at least 2" (width of port) of room in front of the port.I don't know how much room you will have between the back of the box and the rear of the vehicle, this is why I put the ports facing up. If you have the room and can do it, go ahead, I'm not sure if it will sound better or not though.

 

[Vageta31 10+ year member]

I have plenty of space left to face them back so that would not be a problem. You mentioned the slot ports being 7.75"(H) x 2"(W) x 28.5"(L) but I thought slot ports always used the sides of the enclosure. How do I do a 7.75" high slot port when the face of the side it's on is 14.5" internal?

By the way thanks for the help that is almost perfect for what I'm looking for. With 3 cubes net and tuned to 30hz I'm sure I'd be happy with the sound quality and output.

Also about the ports, does it really matter what side of the enclosure the ports go on? For all around cosmetics and risk of things being sucked in I think the sides would work. I have 42" wide to play with but the box is sitting between these 2 small wheels wells that are at least 3" from the side of the vehicle which means I could theoretically put a port near the top of the side facing the side of the vehicle. Not sure if it changes the sound or anything but that's an option.

In reality though whatever is simple and works is fine. I could even do one port if it would make it even simpler.

 

[Trixter 10+ year member]

The reason I went with the 7.75" port is because you wanted two of them. If you made two ports that were 2" x 14.5" they wouls each have to be 53.25" long. That would pretty much take up your whole box. The way to make a 7.75" port is to simply not use the top and bottom of the box and the port walls...just one side. The best port placement will be found by trail and error. I can't say that the top of the box will be better than the side or something like that, each car is different.

If you want it simple, I would suggest having a single 2" x 14.5" port on one side that is 25.25" long.

 

[Vageta31 10+ year member]

If you want it simple, I would suggest having a single 2" x 14.5" port on one side that is 25.25" long.

Then I think I'll go that route. The dual ports may look better but it would add more complexity to making the box. I want something very simple and sturdy. So it looks like I can get what I want from the dimensions I gave which is great. I think 3 net cubes will be enough for now, I can always build a second box later with 3.5-4 and see the difference.

 

[Trixter 10+ year member]

I am doing just the opposite. I have a 5.5cu' box and I'm going to a 4cu' box.

 

[Vageta31 10+ year member]

Oh by the way I want to use T-Nuts or Hurricane nuts to bolt my Brahma to the baffle. How many holes does the Brahma basket have and what size nuts/bolts should I use? Also do I need washers with the bolts?

I'm gonna be building the box tomorrow so I'm just looking to get what I need before I begin. One last thing, assuming the box is cut perfectly and all sides fit flush do I need to use silicone if I'm going to also use liquid nails? Or is the liquid nails and wood screws sufficient?

 

[puppettmaster 10+ year member]

Bs have 8 screw holes in basket

 

[Vageta31 10+ year member]

If I wanted to tune my box lower would it be as simple as making the port longer? Just thinking if 30hz will be low enough, 25hz seems like it will have a lot better low end extension.

 

[Trixter 10+ year member]

I have mine tuned to 24Hz. And yes just extend the lenght of the port to get a lower Freq. The hole size is 1/4"