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DUAL SUBS: Factory vs. Aftermarket


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I did stereo delete and now I really wish I had a black box for Spotify integration. I’m good with the tower light on transfers, don’t do them much. I will order one when my dealership is back open. I don’t think there is an aftermarket version yet identified as 2020 is certainly different. 

Looking forward to seeing what a dual sub under the helm looks like. I just didn’t like the sound from the sealed enclosed. 

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17 minutes ago, timmypop said:

I did stereo delete and now I really wish I had a black box for Spotify integration. I’m good with the tower light on transfers, don’t do them much. I will order one when my dealership is back open. I don’t think there is an aftermarket version yet identified as 2020 is certainly different. 

Looking forward to seeing what a dual sub under the helm looks like. I just didn’t like the sound from the sealed enclosed. 

To be clear, I did not order “stereo delete” this year. in fact, before we dive into the sub project, this is a good opportunity to set the baseline as to what I’m building upon. Let’s take a trip down memory lane as it might help y’all see how I make these decisions...

The last “stereo delete” boat I did was 2017. 

2018 - Factory cabin & sub. All I did was add four Exile Surf 9’s powered by two Exile XM30.2’s. I remember thinking the tower out shined the factory cabin and sub, so...

2019 - I started with the factory cabin & sub. This time I added four aftermarket Rev10’s powered by two aftermarket Syndx4’s. Since I knew that was ALOT, it only seemed logical to replace the factory SynDx6 amp (cabin + sub) with an aftermarket SynDx6 so I could tune it and hopefully get more out of it. It worked!  Cabin sounded great! But the extra horsepower to the factory sub exposed its flaws, hence the original Rip & Replace thread. When I sold that boat it was transformed... the only factory stereo components on it were the cabin speakers and the black box. It sounded SICK, but I felt like maybe more bass was needed to keep up with those Rev10’s (which were getting 400w per can at 4ohm). In total that boat had three aftermarket amps (cabin/sub + tower + tower). I sold off the one factory amp.

2020 - Similar plan to last year, but slight variation... Factory cabin speakers powered by aftermarket SynDx4. Four factory Rev10’s (since Gx tower this year meant I didn’t really want to mess with tower speakers) powered by aftermarket SynDx2.3 HP (yeah, I know... less power to the Revs than last year). As mentioned above, no factory sub... instead build up an aftermarket dual sub setup powered by a dedicated mono amp. So a total of three aftermarket amps (cabin + tower + subs).  I listed my two factory amps last week in the classified and both sold quickly. 


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That brings us to the dual subs. I really like that JL Audio 12W3 last year... way nicer driver than the factory Revo12 (despite similar price points). So I got to thinking... if the 12W3 is good, I bet the 12W6 is BOSS!  I started reading up on a dual 12W6 setup. How would I power it?  I considered a 2 channel amp like the SynDx2.3 HP, the same amp I used for to re-power the factory Rev10’s. But I was advised by a local stereo shop to stick to a mono amp because you don’t want your two subs acting like a left and right speaker. So a plan was hatched to use the JL Audio 1200/1. This amp is sick!  It puts our 600w to each sub regardless of the voltage  or impedance. Say what??  Yup, magic!

So my bill of materials looks like this...


What you see there are the MSRP’s for the JL products. For sure somebody will say, “what about sales tax?”   I have zero relationship with JL Audio.  I simply walked into my closest JL dealer, told them what I wanted (they had to order it) and kindly asked for a little help on the price. They knocked off just enough to cover the 8.25% in sales tax. 

So let’s compare that to the factory dual sub option... MSRP is $3,417. Let’s assume a 25% discount (YMMV), which brings it down to $2,563, very close to my vastly superior JL bill of materials (assuming you are willing to do the work yourself and you actually enjoy these projects so your time is free).

Other options:

If you “downgrade” to dual 12W3’s your JL bill of materials drops to an even $2k. 

If you build @Stevo’s setup with dual Exile Xi12dvc powered by Exile XM15.1 your bill of materials is $1,200. That XM15.1 is a stupid good value at $600 MSRP. 

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I have the 12w6 and three JL HD amps running my system and I am very happy with it. I think you will see that they are better than anything else out there IMO. 

Did you have the factory cut the sub hole for you? Even though I did full stereo delete I asked them to cut the hole and put in a factory grille with seadeck. 

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24 minutes ago, timmypop said:

I have the 12w6 and three JL HD amps running my system and I am very happy with it. I think you will see that they are better than anything else out there IMO. 

Did you have the factory cut the sub hole for you? Even though I did full stereo delete I asked them to cut the hole and put in a factory grille with seadeck. 

I will get to that when I get off my stupid conference calls... all. damn. day.

Bottom line... I love that you got the factory to do that for you.  Good tip for next year.  You will see why when I tell you what I went thru...

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Okay, where to next?  I’ll go in the order I did the project. 

Lets look at the amp board transformation since that’s what I did first...

Pic 1 - Amp board right after pulling it out of the boat. The amp on the right is the cabin amp (OEM Syndx4), and the amp at the top is the tower amp (OEM SynDx2). 

Pic 2 - Amp board after removing the factory amps. Notice the plugs... those plugs lead back to the black box. They both contain signal and remote connections. To connect to aftermarket amps you need adapters (more on that later)

Pic 3 - Laying out the new amps. SynDx4 cabin amp in the same location. SynDx2.3 HP tower amp on the lower left (it’s too big for the factory location up top). JL Audio HD1200/1 goes up top. I can’t believe how small (but heavy) this thing is for a 1200 watt amp! 




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I always try to do as much wiring as possible while the board is OUT of the boat. This minimizes time and frustration inside the “death chamber.”  

Pic 1 - this is the cabin amp with two adaptors:

LEFT: RCA’s and remote power-on. This connects to the black box (plugs seen in the pic above). Note that this adaptor also includes the RCA’s for the sub amp. This is because cabin+amp is all ONE plug and ONE amp in the Malibu/Axis system. Since I’m using a separate sub amp, you see those two RCA’s off to the side. Later I plugged them into the JL amp. If you need this plug you can make your own using @Ronnie’s instructions or you can buy them from Exile Audio or search eBay where there’s a guy who sells them.

RIGHT: this adaptor is for the speaker wires for the 8 cabin speakers. This plugs into a plug that’s left behind in the boat. You can either make this plug or just cut off the one inside the boat and splice your own speaker wires in.

Pic 2 - Same as Pic 1 only this time it’s the tower amp  

Pic 3 - This is the 4ga wire for the sub amp. I like using ferrules for a clean install. 

Pic 4 - The 10ga speaker wire I bought for the subs. That’s pretty thick speaker wire but I figured the 12W6’s need to drink!  Super important to buy OFC wires, not CCA.  Also important that your wires match your boat!!





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Last few pics of the amp board then we will move onto subs!

Pic 1 - complete and ready to put in the boat. 

Pic 2 - getting into position, plugging speaker wires into factory harness, routing power and ground cables into the right spot. etc 

Pic 3 - adding a third fuse to the Gabriel distribution block (for the third amp)

Pic 4 - Done!!





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Let’s talk about box design... last year I was trying to build a box that would fit thru the factory cut hole under the helm, but was also optimal for the 12W3 which calls for 1.125 (net).

This year the goal is slightly different.  For starters, the 12W6 specs call for a smaller enclosure at 1.0 (net). Also, while I still want sub #1 to fit in the factory helm location behind the factory grill, I also would prefer if box #2 was the same exact size and shape. I realize there is more than one way to build a 1.0 box, but making them identical just felt easier during the cutting and build process (less math and fewer unique cuts). 

While a smaller box should be easier to fit under the helm than last year, I was worried because I have a 5-outlet heater this year (more on that later). I also had this to consider... is sub #2 going in the factory / @G Spot location (under the OB seat) -or- in the @Stevo location (inside the death chamber)?  Honestly I felt stumped. Then it hit me... build a box that can fit all THREE locations. That way I can decide the location of sub #2 later, and if I change my mind down the road I can move it! 

So here’s what I came up with. Remember from the “Rip and Replace” thread, you can’t really be much deeper than 12” for sub #1 under the helm. I also knew that @G Spot’s sub #2 under the OB seat was in the infamous QBomb (which at 1.325 is way too big for a 12W6) which meant width and height of that box worked down there. So I simply spec’d a shallower Qbomb. Once I knew the dimensions I made sure it worked under the helm.  The bonus was that because it was a bit smaller, I didn’t have to notch the back corner like last year to fit under the helm. This greatly simplified the build. 

Here are my final calculations:


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Next step was just to cut out and build the boxes. Pretty basic project actually. 

Pic 1 & 2 - cut out pieces 

Pic 3 - cut out hole

Pic 4 - glue and nail together







Edited by IXFE
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Pic 1 - lots of stainless screws

Pic 2 - silicone on all joints, inside and out

Pic 3 - wood filler screw holes 

Pic 4 - round edges with router 

Pic 5 - sand smooth

Pic 6 - ready for waterproof coating







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Now that the boxes are ready, time to get back to the boat...

As much as I’ve been critical of the factory sub, I do like the way it looks  I’ve always been a fan of retaining the stock look and feel.  So that meant sourcing the factory billet grill and soft touch... my dealer rolled this into my boat price, but if memory serves, it was aprox $300 for both pieces. I guess I should have added that to my bill of materials... oops! :dontknow:

Pic 1 - marking off the hole (outside edge of inside tape line) making sure to leave 1” lip 

Pic 2 - factory billet grill. notice how it’s darker this year, but why do they print the part number on the front?

Pic 3 - factory soft touch to match my floor (graphite). This was a hard piece to get for some reason. 

Pic 4 - backside of billet grill, double checking screw holes have enough fiberglass lip. 





Edited by IXFE
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Next step was to think thru the location of sub #2, much easier to do now that I had an empty box to play with. I was kinda nervous to see if my theory of building a shallower Qbomb had worked!

Now I know what you’re thinking... with the fiberglass taped off, why not cut the hole next? Honestly, I was procrastinating that part as I really wasn’t anxious to do it.

First I tested the factory location (beneath OB seat) 

Pic 1 - What that spot looks like empty 

Pic 2 - to get the box into that spot, you must start at the rear and push the box all the way forward... thanks for that tip @G Spot

Pic 3 & 4 - it fits! But since the floor isn’t level it would be a challenge to give the box a solid foundation. 

Pro - retains OB compartment storage and amp access

Con - challenging location to install/secure the box, likely to rattle cup holders






Edited by IXFE
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Next I tested the death chamber, which is where @Stevo has his 2nd sub. To fit here I had to flip the box up on its side. 

Pic 1 - fits nicely, but there are a couple of issues: a) the floor isn’t level at the seam, and b) this location will make access to amp adjustments difficult. 

Pic 2 - in addition to being easier to install, one thing I like about this location is the fact that the two subs are in virtually identical locations (mirror each other). In home theater the ideal location for dual subs is front stage, in the corners. So why not do likewise in the boat?



Edited by IXFE
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I decided to go with the death chamber location for sub #2. But I had to solve the uneven floor issue. You’re probably wondering why the floor is uneven.  That seam in the floor is fiberglass on the left and starboard on the right. They are actually the same height, but then Malibu puts soft touch on the fiberglass bringing that side up about 1/8 of an inch.  The starboard on the right is left bare, probably because nothing sticks to it  

To level it off I procured a small sheet of abs plastic from the local stereo shop (free of charge). I also bought some dynamat from the same shop. 

Pic 1 - ABS plastic 

Pic 2 - Testing if it’s level 

Pic 3 - Screw it down

You can’t see in the pics but I put a piece of dynamat on that ABS plastic before screwing it down. I’m not a fan of having plastic on plastic   




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Pic 1 - I split a 12oz bag of poly fill 

Pic 2 & 3 - These are the speaker wire terminals I use... not a fan of those cheap plastic ones you see on prefab boxes 

Pic 4 - I like to use this stuff to seal the woofer hole  I’m sure it’s overkill, but it makes me feel better  

Pic 5 - Coming together 

Pic 6 - Done!


Note: you can’t build sub #1 like this. Only build sub#2 before putting it in position  

Also, I screwed up on this part, and I have to go back and pull this sub apart... anybody know why?







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Sub #2 complete!  What you can’t see is that I put a layer of dynamat on the bottom of the box. Also, I debated whether or not to screw this box down. Ultimately I decided I didn’t want it loose in there. So I secured it with three black L brackets that you can’t see unless you’re looking for them 




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