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Discussion Starter #1
I have a Genz Benz LS 118 B subwoofer that I am thinking of adding a bottom firing speaker to.
I have an EV 12" subwoofer that I acquired here from marcos.

Right now i have the 12 in a sealed cab and am running each speaker with a separate bridged amplifier.
I want to combine the speakers to make things more compact.


I would appreciated any ideas or thoughts before i fire up the power tools.

cheers
ets
 

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Not to be a party-pooper, but...........

A speaker (i.e. speaker box and driver combined) is a system. The box, by some estimates, is about 75% or more of that system (changes in it will have more impact than a change of drivers). Modifying may do more damage than good, depending on many complicated factors (stiffness of box, phase cancellations, etc).

Besides the compactness, is there anything else you are unhappy with in the existing sub? Is there any way you can do this as a reversible mod? If no to both, I would be careful proceeding forward. Maybe more internet research? Again, don't want to poop your party.
 

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^ yeah pretty much.

That said, there is a few ways you can do it:

1) make a dipole system - this requires 2 identical drivers, wired out of phase so that when one pushes out the other is pulling in and box volume becomes almost irrelevant. Your other driver is not the same so this falls off the list

2) make a passive radiator system. Assuming the box is acoustic suspension (sealed vs ported) you can add the second driver but don't connect it to the amp/jack. It will turn the sealed box into PR, which is similar to bass reflex in performance. This will be a crapshoot as regards tuning, but you can tweak it by adding weight to the down firing passive cone (replace the dustcap with a pc of cardboard with a bolt through it so you can add washers; paint the cone with waterred down white glue/wood glue/puzzcoat/mod podge - this has the added bonus of stiffenning the cone and lowering resonance).
 

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Discussion Starter #4 (Edited)
Thanks for the feedback I think I will look at designing an extension section to the bottom of the cab and make it a sealed/ infinite baffle enclosure... that will leave the 18 as is
 

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Discussion Starter #5 (Edited)
so i opened up a 12 x 12 inch square in the bottom of the sub woofer box and mounted the baffle and speaker to the out side of the cab. running the signal through an eq, to an ashley compressor to a stereo outboard x over then to mono amps for each speaker.
sounds good so far and the set up lets me find a balance.

next step is to build up a collar on the bottom and cap the opening i cut to create a sealed space for the 12 and remove the temporary 2x4 caster blocks
.
 

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