Bass (Space) Saver: Z1 Subwoofer Enclosure + AudioControl SPC-10S4

It’s been a while, right?

Okay so – I had been putting off a minor issue with my car audio system for quite some time—until just before Labor Day 2026. The timing worked out because Z1 Off-Road was offering a Labor Day discount, which finally motivated me to tackle the problem (while saving some cash, too!)

Here’s the situation: the prefab subwoofer enclosure I was using often caused rear passengers to bump their calves on the forward corners of the rear bench seat. Take a look at the left side first:

And then the right side:

side:

To address this issue, I decided to replace the existing dual-subwoofer enclosure with the Z1 2005-2021 Frontier Subwoofer Enclosure (Crew Cab). This enclosure is specifically shaped to fit a single 10″ subwoofer underneath the right-side rear seat. Technically I was downsizing from my current setup, but to be honest, having two JL Audio 10TW1-4 subwoofers was always overkill. Moving to a single subwoofer solution should should still be more than enough bass output for the Frontier’s small cabin.

A few days after placing my order, the guy in the brown truck delivered three boxes to my doorstep:

Inside box #1 was the Z1 Off-Road Frontier Driver Side Under Seat Storage Tray, which I ordered to add storage to the left-side area that had previously been occupied by the large 2×10 subwoofer enclosure:

Inside box #2 was… the right-side Molle bracket, wiring harness, a sticker, and other installation goodies for the new enclosure:

And finally, in side box #3 was the Z1 Off-Road subwoofer enclosure itself:

The enclosure is not made out of fiberglass or MDF, it is molded out of a plastic-like material that feels pretty dense and stiff enough to handle low frequencies. There is a single cutout for a 10″ sub and a provision for the included speaker terminal plug. The outside of the enclosure has a nice texture that will blend in with the Frontier interior. No speaker mounting hardware is included (8 screws is too much to ask for LOL) but you get a Z1 sticker instead.

I ordered the enclosure unloaded (no speaker included) because I wanted to see if one of my current JL subs would fit; the specs seemed to be very close, but the only way to find out was to actually try it – so I did, and:

…no luck. The way the Z1 enclosure is formed, the top-mount depth was very different from the rear of the opening and the front of the opening:

Now I can see why there was not a simple “mounting depth” measurement listed on the Z1 website… instead you get this formula to calculate if a particular subwoofer will fit. Okay – so since I needed a new 10″ subwoofer, I went on the hunt. I checked the specs of many subwoofers from JL Audio, Sundown Audio, Focal, Hertz… and guess what? NONE of them would fit because either A. the mounting depth was too low; B. The voice coil size would not clear the Z1 enclosure shape; or C. The driver mounting hole diameter was too big.

However – every measurement of the AudioControl SPC-10S4 Space Series shallow-mount 10″ subwoofer was perfect for the Z1 enclosure (which makes sense, in hindsight). I don’t know this for sure, but I strongly suspect that when Z1 designed this enclosure, they might have designed it around that one specific subwoofer driver.

Okay so with that said, I ordered one – but not from Z1. The Labor Day sale was over (LOL) but I had $10 in Crutchfield rewards points AND Crutchfield also gave me another $10 off if I chose “no rush shipping” – so I bought the sub from them! Within a few days, the brown truck dude dropped off box #4, and it contained this:

I have used many AudioControl products over the years, and by just looking at the AudioControl SPC-10S4, you can tell that it’s a good addition to their product lineup. The subwoofer is built well (and is pretty heavy!) with a large voice coil, mica-coated cone, premium spring terminals, metal mesh grill and a pre-installed rubber gasket. Oh and HEY they also include mounting screws.

Now that I have all the ingredients for my subwoofer revision, it’s time for the install. The first thing I did was install the wiring harness… and then I noticed that Z1 did not give me two screws for mounting – there was only one in a sealed bag (QC anyone?):

Of course, I did not have any M3x10mm countersunk machine screws in my garage, so I had to take a trip to the hardware store JUST FOR ONE SCREW BRO.

Back home after buying a pack of 20 screws when I only needed 1 (LOL)… I had the wiring harness installed, along with the foam silencer tube. I took the liberty of adding some polyfill to the Z1 enclosure before installing the subwoofer:

The end result is a very clean  and sleek look (I like it!):

One more step before actually installing it into the truck – I had to install the Molle bracket to the side. This was easy, as it only needs two bolts for attachment, and the enclosure had pre-installed threaded inserts:

Moving along quite nicely… I removed the old sub box and did some quick vacuuming:

Next, there are a pair of rubber bushings that need to be installed into the existing brackets/tabs on the floor of the Frontier:

Next I wired in the included speaker harness to my existing subwoofer output; I thought I took a photo of this, but apparently not – so here’s a photo of the completed plug ready to go:

The Z1 enclosure simply presses into place; two metal pegs at the bottom fit perfectly into the rubber bushings, and the completed installation looks clean and discreet:

with the sub enclosure in place, istalling the Z1 Off-Road Frontier Driver Side Under Seat Storage Tray was all but 2 minutes – it simply bolted to the existing floor brackets with a pair of bolts:

Installation is complete! Here’s the before/after comparison:

The overall size of the Z1 subwoofer enclosure and the matching storage bin is very compact, as neither extends forward into the floor mat like the old subwoofer box did. With the extra space freed up, I can now store gear in the bin that used to be tucked behind the seatback, with plenty of room for additional items if needed:

Finally, the problem is solved – both the subwoofer enclosure (including the Molle bracket) and the left-side storage bin do not protrude at all past the rear seat bench. Both are set in deep enough to be non-intrusive and passenger-calf friendly:

As for the bass, I can describe it in two words: just right!

With my tried and true Alpine PDX-V9  amplifier pushing up to 500w into the single 10″ sub, bass is still abundant. Sure, it doesn’t hit quite like the dual 10″ JLs I ran for years, but that’s expected. What surprised me is how strong the SPC‑10S4 is even as a single sub. The bass output is tight, controlled, and free of boominess, and if I push the bass level knob too far, it still produces more output than I realistically need (which is a good thing!)

So the subwoofer revision is completed. I still have tight, punchy bass but I also gained some storage space and (the best part LOL) no more passenger complaints of hitting their leg on the subwoofer enclosure. I’ll take that as a win-win =)