My new double sub box...

[ZachDaddy]

Here are a few pictures of my sub box... It will hold 2 JL 12w6v2's and powered by a JL 750/1 HD amplifier.

[reftech]

Dayumm!! That should give u tons of bump!! I'm only running one 12 and it rocks. Can only imagine 2!

[EarmarkMarine]

Is it down-firing?

David

[bsloop]

I assume the proper math was done on port size and what will be tube length but it seems rather small given the volume of air pushed by two 12's?

[EarmarkMarine]

Is there a port?

David

[ZachDaddy]

@David...Yes it is a down firing box. It is not ported though. The space that it has to fit in would have required me to modify the seat base top. I chose the sealed box again but add another JL 12w6v2. They did tell me that I could have gotten the same output ported with my single JL12 but didnt want to cut my baby!


Question for you: I have been told that my JL 750/1 HD amp wired in series will deliver 750 watts to both subs at max power and that adding the secound 12 has increased volume by 3db's is that correct? Both are getting 750 or each is getting 375?

Ordering my SD4 from Odin after tax time...your peeps are the best! Thank you for your time on all the forums that you help out on...

[ZachDaddy]

It has to fit in here...I was told the box was tuned to 38 hertz. This is the single seal box that I originally had built for a different boat and it was tuned to 34 hertz. The bottom of the box is flat and the hull falls at an angle. The surround was hitting the right side here and wore a hole in the surround. A costly mistake.

[Aric'sX15]

Wish i had room for a set up like that! heater gets in the way!

[bsloop]

My error, I see the 3rd hole is a terminal connection.

In a theoretical world, there is a 3db gain with the additional sub using the same power.
Another 3db can be gained with a doubling of power.

Short answer, ideally you have 750w that will now be split between both speakers.
Class D does NOT double output with reduced resistance like class A/B. ie, prior was 2ohm, new 1ohm.

Amp is rated 750w at a minimum of 12.5 volts, COLD! As voltage drops, output will fall. As it gets HOTTER, it reduces power in an attempt to not go into protect.
Using only the existing amp for both subs leaves no head room and will work it even harder as voltage falls.
The previous set up was powered about right with a little head room that still gave it good power by end of the day.
The new set up should play louder than before but will leave you significantly underpowered by days end. Not a problem if you are disciplined but if you are like many, expecting more volume and not hearing (or smelling) when the subs are getting stressed, the money saved by not adding another amp might be lost replacing subs.

[EarmarkMarine]

Originally Posted by ZachDaddy

@David...Yes it is a down firing box. It is not ported though. The space that it has to fit in would have required me to modify the seat base top. I chose the sealed box again but add another JL 12w6v2. They did tell me that I could have gotten the same output ported with my single JL12 but didnt want to cut my baby!


Question for you: I have been told that my JL 750/1 HD amp wired in series will deliver 750 watts to both subs at max power and that adding the secound 12 has increased volume by 3db's is that correct? Both are getting 750 or each is getting 375?

Ordering my SD4 from Odin after tax time...your peeps are the best! Thank you for your time on all the forums that you help out on...

The JL Audio HD750/1 will deliver the identical power with any load from 1.5 to 4-ohms and with any supply voltage from 11 to 14.4 volts because it is strictly regulated.
In theory doubling your woofer surface area will provide +3dB. But each woofer is now getting -3dB power. You will net a gain but not +3dB. If you add a second HD750/1 you will net a real gain of +6dB.
You might cut in another terminal cup in preparation.
A couple of suggestions on the enclosure...
Line the bottom surface with 0.5" thick HDPE pads. This will keep moisture from wicking up into the porous end of the MDF.
Notch out the legs to allow greater surface area. As it is you will benefit from the gain of boundary loading off the sole but you will also lose some output from reducing the radiating surface area.

David