Custom Box for Truck; Size constraints - Help & Tips needed

[Memnoch]

Hello, this is my first post here! I am trying to build a sub box for my sons truck. It is his first truck, and we got him his first sound system for Christmas. There is of course size restraints on the box dimensions and I just want to get some feedback before I start cutting anything to build his box. The previous owner had some sort of subs installed, and the wiring is all still intact. The line to the battery is there, the ground is there, and the connections and remote line for the amp are all ran and connected to the deck already. I did purchase a wiring kit though in case but it doesn't look like I will need any of it except for the speaker wire to wire the subs themselves to the amp.

The 2 sealed boxes that the audio place sold us cut out the holes too big, and we won't be able to return them for a while (time and distance from us). So I purchased an 8x4 MDF sheet and the screws, glue etc.. to put one together myself. He would prefer a single box to 2 boxes if that is possible. Details are in the list below for the vehicle and subs etc.

Vehicle : 2001 Dodge Ram 2500

Location in the vehicle: Behind the seats

Space available (Length x Width x Height): 63 1/2" L 8 3/4" W 30" H

Subwoofer make and model: Massive UFO 12" shallow sub

Subwoofer Size: 12

Number of Subwoofers: 2

Type of Port (Kerfed, Slot, Aero, etc.): (unsure)

What type of music do you like?: He listens to pretty much everything but probably heavier on rap

Is your goal SPL or Everyday Music?: Everyday

Tuning Freq (Hz): Unsure

Volume : Unsure

Questions:

Recommended air volume is 1 Cubic Ft per sealed box per 12" sub. The only other recommendation I can find on the spec sheets for the sub is a dual ported box which is 3.11 cubic feet. But the dimensions of that box will not fit his space due to the limited depth of 8.75".

I have come up with a simple rectangle design for the box as follows:

34" long
18" tall
8.75" wide

with the .08 displacement of each sub that would give me roughly 3.13 cubic feet of air space, which is pretty close to the ported recommendations but there is no port on this. Would I add a port or would I need to adjust the dimensions of the box to reduce the air space? Should I add braces inside the box (which would further reduce the cubic space); if so would the dimensions need to be adjusted further?

Would it be better to seal in each sub on the box (ie adding a wall for each sub or a wall between them)?


Please let me know if I am missing anything or if there are any questions. Any help is greatly appreciated!

Click to read more...

 

[Doxquzme Premium Member]

Increase the width to 42". Run a brace in the middle (see lousy drawing) leaving at least 6" to the port opening use a 4" flared port 6.75" long (including the flare) as pictured. That should get you real close to that which is recommended by the manufacturer.

With a center brace you will support the middle of the box enough in my opinion. Being that it is as shallow as it is, only the front and rear panel are to worry about and that brace in the middle should suffice.

 

[Memnoch]

Increase the width to 42". Run a brace in the middle (see lousy drawing) leaving at least 6" to the port opening use a 4" flared port 6.75" long (including the flare) as pictured. That should get you real close to that which is recommended by the manufacturer.

With a center brace you will support the middle of the box enough in my opinion. Being that it is as shallow as it is, only the front and rear panel are to worry about and that brace in the middle should suffice.

thanks for the feedback. I have been digging a little deeper and came up with this, tell me what you think:

so if the math is right this box that I did in sketchup ends up at 34" long 18" high 8.75" deep, it has a partitioned piece in the middle that is 3/4" L (depth of the mdf) 18" high 8.75" deep, with 2x 4" holes 12" deep, and that comes out to 1 foot of cubic air space on each side, (the depth of speaker and pvc pipe are already reduced from that total) and the port on each side is 4 5/8" from the partitioned space. The spec sheet recommends 1 ft of cubic air space for each in its own enclosed space and for the port to be approx. 4.5" from the wall. I think with this I am hitting all of those numbers pretty closely. Thoughts?

 

[Doxquzme Premium Member]

From the Massive site:

Recommended internal volume of 1.2 each AFTER dispament. When accounting for the two drivers, the brace(s) and the port displacement, the internal volume needs to be around 2.8 to 3 cubic feet. The recommended tuning frequency from the manufacturer is 38hz, I'd drop that down to around 34 hz - the driver fs is 33.2, I see no reason not to be at or 3db down from the resonant frequency of the driver. Dual flared 4 inch ports 12 to 18" long accupy around .21 to .25 cubic feet. A 3 cubic foot gross internal volume, is what you should shoot for.

If you can get the box up to 3 and tune it to 34 using dual 12x4 inch flared ports, you should be good to go.

 

[Doxquzme Premium Member]

Put the ports on the same side, not opposites.

 

[Memnoch]

Spec sheet shows different values from the website, not sure why that is. Shows on the sheet that came with the sub 1 ft for a single ported enclosure; 1.56 for a larger one, 3 ft for a dual enclosure with 1 single port. Essentially the box I did is 2 boxes, but moveable as 1. Each sub has it's own single enclosure and port, that was why the ports are on opposite sides, the middle is closed off. Is that wrong? Should I shoot for a larger box with just a single port to increase the air space and not separate the subs? Also, oddly the spec sheet says 45hz for small ported enclosure and 42hz for large. Those are pretty big differences than the site.

Added another angle of the box to see the enclosure and the 4 5/8" space from the wall

 

[Doxquzme Premium Member]

Sorry , I did not see that the sides were divided by the brace. That is fine, in some ways preferable in the event that you blow one, it doesn't take the other out too (not a likely scenario). I would go with the largest recommended size you can fit. Often manufactures are looking for the biggest, loudest boom. This often means a real peaky SPL box (think large 16" floor tom instead of large bass drum), not a great sounding box. Two 12's in a truck cab is going to be substantial, shoot for the bigger, better sounding ported box, tuned no higher than 38, I'd be looking at 34 hz.

Using your split box (dual individual ported sides) 1.5 ea. side (vb 1.29) cubic feet for each side, a 4" port is going to need to be 20" long, which means you will have to use elbows to get them to fit in each side.

In a 3 cubic foot shared enclosure box (vb 2.58), two 4 " ports are the same 20" but theres is plenty of room to accommodate the port length.

Two 4" ports are not going to have as much of that port noise (farting sound if you will) either.

 

[Memnoch]

Sorry , I did not see that the sides were divided by the brace. That is fine, in some ways preferable in the event that you blow one, it doesn't take the other out too (not a likely scenario). I would go with the largest recommended size you can fit. Often manufactures are looking for the biggest, loudest boom. This often means a real peaky SPL box (think large 16" floor tom instead of large bass drum), not a great sounding box. Two 12's in a truck cab is going to be substantial, shoot for the bigger, better sounding ported box, tuned no higher than 38, I'd be looking at 34 hz.

Using your split box (dual individual ported sides) 1.5 ea. side (vb 1.29) cubic feet for each side, a 4" port is going to need to be 20" long, which means you will have to use elbows to get them to fit in each side.

In a 3 cubic foot shared enclosure box (vb 2.58), two 4 " ports are the same 20" but theres is plenty of room to accommodate the port length.

Two 4" ports are not going to have as much of that port noise (farting sound if you will) either.

Nothing to apologize for! I appreciate the help! So by going bigger, is there a limit? I mean I could make a box that is 63" by 27" (8.75" deep) easily enough, but that would result in around 6.58 cubic feet (not counting ports, subs etc)...is that to big, is there a number I should really target between 3 and the 6.58?

 

[Doxquzme Premium Member]

Sorry, should have clarified, 3 cu ft gross is optimal from what I can see. Dual 4 inch flared ports 20" long. A single center-ish brace can act as both a brace and port support if mounted so that the two ports terminate at the braces end (don't want to the brace to extend the ports length) so through and flush with the brace.

Slightly to one side where the end of the ports would sit in the brace, completely around or half as pictured. Hole in the center is optional on the half-length brace, one on each side if full brace used.

 

[Memnoch]

Sorry, should have clarified, 3 cu ft gross is optimal from what I can see. Dual 4 inch flared ports 20" long. A single center-ish brace can act as both a brace and port support if mounted so that the two ports terminate at the braces end (don't want to the brace to extend the ports length) so through and flush with the brace.


Slightly to one side where the end of the ports would sit in the brace, completely around or half as pictured. Hole in the center is optional on the half-length brace, one on each side if full brace used.

Thanks for your help, let me know if this final workup looks good. I think I have it all ready to cut. Inner dimensions are 21.75" x 18.25" x 7.25", which gives me about 3.56 Cubic feet of air. Not 100% how much the brace takes away from that, and the pvc you said was roughly .25, so I would think the brace is less than that which should put me pretty close to 3.11 total inside.

My brother in law who is supposed to help me tells me that this box design is trash and that I don't know what I am doing and that I don't want ported box in a truck either. So I don't know. Second guessing myself now, even though the spec sheet recommends a ported box and brace and it seems like I am hitting all the correct numbers for best performance.

 

[Doxquzme Premium Member]

Nice, yes, that will do it!

 

[Doxquzme Premium Member]

Well, you know what they say about opinions, they are like a$$holes, everyone's got one! In order to get the most bang for buck out of those woofers, and in lieu of the primary beneficiary of the sound they will create, I definitely think that ported is the way to go. Sealed is often equated with SQ systems, and in some reaposects that is true. That said, this driver sealed produced a pretty high f3 of around 43hz, which is the 3db down point from 46 hz, pretty high for a 12". I was able to get the QTC down to around 710 when modeling it and that is around 34 hz, ported, not sealed. Sealed remained around 757 which is fine, but a little lower is fine too.

A Qtc = to 0.707 is the optimum value for sealed enclosures, providing flattest response and highest SPL for deep bass extension. This box gets you close.

IMHO. Not sure what criteria the broski-in-law is using, but more often than not, a little knowledge is more dangerous than complete ignorance.

At any rate, with cabin gain and the lower tuning point, I think that your son will be very happy with the results.

 

[Doxquzme Premium Member]

One other thing, if you plan on using 4" pvc, make sure to take a 3/4 inch roundover bit to the outer edge of the port opening on the box, reduces win noise and chuffing, Creates an easy flare without having to purchase one (and it looks a lot better too!).

 

[Doxquzme Premium Member]

Or pick up a couple of these. Take a piece of 5" square leftover MDF, cut a 4" hole in it, mate up and glue the PVC to the back (to required length), good to go, neat and sweet!

Amazon product ASIN B071CLLVYK

 

[Doxquzme Premium Member]

Thanks for your help, let me know if this final workup looks good. I think I have it all ready to cut. Inner dimensions are 21.75" x 18.25" x 7.25", which gives me about 3.56 Cubic feet of air. Not 100% how much the brace takes away from that, and the pvc you said was roughly .25, so I would think the brace is less than that which should put me pretty close to 3.11 total inside.

My brother in law who is supposed to help me tells me that this box design is trash and that I don't know what I am doing and that I don't want ported box in a truck either. So I don't know. Second guessing myself now, even though the spec sheet recommends a ported box and brace and it seems like I am hitting all the correct numbers for best performance.



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Here is the specs from the Massive. Which indicate after displacement, 3.11 is ideal and your going to be darn close if not almost dead on.

https://cdn.shopify.com/s/files/1/0658/1297/files/ufo-series-manual.pdf?v=1484992975