Hey guys, I did some pre fitment for a SI BM mklll box build. In my truck an 07 SC, a 3.5" tall box fits all the way to the back wall under the seat, with a two inch gap under box for a downfire configuration. Box will be 18 or 19" width. Just need to figure legnth for appropriate box volume. Just add additional wood on top of box to blend into bottom of seat for cosmetics wise. Maybe put a 45 on front edge.

 

I will be following this i also bought 2 of these bitches..what amp are you running with em?

 

Well I will only have one. Zapco Ref 500.1. Need to really match wattage to box on these.

 

yea i was thinking JL 750/1 but thats too little for 2 and JL 1000/1 is good but its kinda big...so I am currently looking around...how do you like the zapco's?

 

I believe at .5cube need to be around 450 watts. As box grows, wattage needs to come down. This sub is very efficient. Great info on the SI and DIYmobileaudio websites.

 

I never owned one before, but I have read good reviews. mSall150 pointed me in the directions of a used one on the DIYM site that I picked up at a smoking $135. Im no audio expert, just what I have read on a few sites, but that JL750 should work for ya if you build box just a tad over spec. You will need to build two seperate boxes to get airspace right. I think one box might put you a little high on the airspace. Again, Im no expert, just using my own rationality. Your drivers box should be easy rectangle build with a 2 inch small foot on front. Back edge of both boxes will sit on rear hump at rear of seat. I need to measure the space on the jack side to see if you can get the airspace needed within the frame, but you may need to extend the box just in front of middle frame leg similar to a one box design to get box to your specs. Play around with sub volume calculators on web to come up with perfect design. Well at least we know a 3.5 dept box can fit under the seatpan flat in a downfire box. Just cut you a 3.5" test piece of wood for test fitting. I will be adding additional pieces to the top/front of box to match up with lower seat. They will be solid pieces just for cosmetics cut on a 45 angle.

 

Now that I think about it, that JL1000 in a spec box with gains turned down would probably be perfect. I don't know, but either amp would work. I'm putting 500 watts to one speaker in spec box (.5 cube) as SI is recommending. Also, they will only warranty up to 450 watts per speaker, FYI. Go to their site, read the faq's in the SI forum.

 

http://www.subthump.com/f150.htm


wonder if I could use this and mod it to fit the 12's




or this box too


http://www.fadfusion.com/selection.p...er=20082405672


I am waiting for Msall to chime in as I believe he has the cheapo box so he may know


I'm not going to lie I am kinda lazy to build a box so if I can get away with modding one I sure as hell will

 

You can modify A box as long as there is room. It is all the same. Marcus1033, the mounting depth of the speaker is 3.5. Your box needs to be deeper than that. It appears that the bm has a pole vent. The speaker needs to cool. The inside height of your box will need to be more than 3.5.

 

No the mounting depth is 2.75 when the speaker is mounted onto a 3/4" MDF board. On a 3.5" box you have a 2" gap under box, so I could add 1/4 or 1/2 inch spacer to bring pole vent away from back wall. This is going to be a great thread, anyway I copied and pasted the FAQ sheet from SI forum to answer everyones questions about the new BM mklll.

BM FAQ:

What is the mounting depth if mounted on a normal ¾” piece of material?

When mounted to a ¾” piece of MDF or other material the mounting depth of the BM mkIII is 2.75”.


What size enclosure can I put the BM mkIII in?

For optimum performance the enclosure volume can anywhere between 0.42 ft^3 and 0.55 ft^3 sealed. We highly recommend stuffing any sealed subwoofer enclosure with polyfill and/or fiberglass insulation.


Can I put the BM mkIII in a smaller enclosure or a larger enclosure?

Yes you can. However, power handling and/or low frequency extension will be affected. The BM mkIII has been engineered to provide optimum performance in 0.5 ft^3 sealed. Making the enclosure volume significantly smaller than recommended will cause a reduction in low frequency extension. On the other side, making the enclosure volume larger will significantly reduce the power handling of the driver.
If you make the enclosure smaller than recommended, we highly suggest using an aperiodic membrane such as a ScanSpeak Variovent.
Making the enclosure larger will diminish power handling as follows: In 0.75 ft^3 power handling is reduced to 400 watts. In 1 ft^3 the power handling is reduced to 300 watts.


How much room does the BM mkIII take up inside the enclosure?

The BM mkIII 12” subwoofer displaces 0.05 ft^3.


How much room do I need behind the subwoofer?

If you have no other choice, you can put the back of the BM mkIII 1/8” away from the back of your enclosure. Ideally there should be ¼” to ½” of space behind the BM mkIII.


Does the BM mkIII need 450 watts to perform?

Absolutely not. The new BM mkIII is a very efficient subwoofer thanks in part to its XBL^2 enabled motor and it does not need every bit of its power handling limit in order to perform well. In its recommended enclosure volume of 0.5^3 sealed, the BM mkIII’s ideal power range is 200 to 450 watts.
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Stuffing an enclosure (we recommend lining the walls with fiberglass insulation over using polyfill) reduces internal resonances which smooths out the overall response. It also fools your subwoofer into thinking it's in a larger enclosure. For instance, if you had an enclosure that was 1 ft^3 and you stuffed it with a pound of polyfill the subwoofer would think it's in 1.25 ft^3. I.e. it will play lower.

 

My only question with those boxes is that can you open up a big enough hole on those spacers. I would call the company to get exact measurements on those spacers.

 

I need to retract my statement about two boxes. After playing around with a volume calculator, it looks like you will have to build one solid box to get the needed volume. It looks like the perfect box for an 04-08 SC for a single new BM would be outside measurements of 3.5 x 18.5 X 27 which equals 0.502 cuft. I didn't realize the box needed to be so long. Must be loosing alot of airspance not being able to put top of box on an angle. I will check the clearance over the entire hump when I get home.

 

bada bing. i thought the same thing about opening up another box. There are plenty out there it will work with.

 

here is one. I dont know what the baffle to floor clearence is.
http://cgi.ebay.com/ws/eBayISAPI.dll...=STRK:MEWAX:IT

 

I will be building my own box for the BMs using an upfiring design.

Also, you guys are worrying too much about getting the exact amount of power. As long as your amp does 300+ per sub you should be fine, these subs are efficient. If you amp does more than the BM's rated then that is also fine, turn the gains down properly and the amp wont have to work so hard which reduces heat and reduces possible distortion. My 2 BMs will be seeing a combined 1200 RMS from my Cadence iA7.

Oh also, the BM has no pole vent. Nick stated that you could literally put the back of the sub up against a wall (or 1/8" away so it doesn't vibrate).