Footwell Subwoofer Install

Bass for a tiny car.

Bass for a tiny car.

Here’s something I’ve not had in decades and never in a Miata – bass. Some of my past cars had stereo systems. But since buying Sharka in 2000 I’ve been in tiny speaker land.

Tiny speaker land really isn’t so bad.

One day I was kicking back, browsing forums, and I came across an ad for a footwell speaker box. I realized that I almost never have a passenger in a Miata with me, and when I do, she’s not even 4′ tall and her feet don’t touch the ground. And it’s gonna be a while before they do touch.

Visions of speakers filled my head.

Stock trunk area.

Stock trunk area.

Tons of leg room.

Tons of leg room.

Bucky is the car being modified this time. Sharka usually gets all the love, but Bucky seemed to be eager for some stereo upgrades. Bucky is sort of my daily driver since I drive the little guy most days and drive Sharka roughly twice a week. I figured I’d get more use out of a stereo upgrade in Bucky.

The above shots are quicky “before” pix. Stock footwell, stock trunk. Nothing special.

Black Roadster Footwell Subwoofer

Black Roadster Footwell Subwoofer

This footwell subwoofer box comes from a guy named William, who I’ve known for damn near all of my Miata driving days. He was a member of the forum (The Darkside) back in the day. I spent all of my hours there. We’ve chatted a lot over the years. I should have bought one of these sooner.

William has been making these footwell sub boxes for years. It’s just something he does in his free time. He has no store front. You can find him under “black roadster” on most of the various Miata forums and I’ll include better contact info at the end of this post. The sub box went for roughly $150 shipped at the time of this blog post. It comes without speaker or amp.

March 2018 update

You can now order a footwell subwoofer box of your own straight from William! Go to to claim yours.

Boom boom wiring.

Boom boom wiring.

The box is really impressive to me. I know next to zero about building speakers or boxes or matching speakers to boxes or… well… anything about car audio. I’m truly NOT the person to be writing a car audio review, but I’m doing my best.

Anyways, the footwell box is sized to fit the NA and NB left hand drive Miatas. Mine fits in my NB perfectly, which is something I was ever so slightly worried about. They have small differences in footwell shape.

It comes with wiring, polyfill, and terminals. The box volume is .26 cubic feet. Polyfill increases the effective volume (or so I read). The front edge is carpeted.

It’s lovely, really.

Wires clipped on.

Wires clipped on.

Rockford Fosgate P1S4-8 installed.

Rockford Fosgate P1S4-8 installed.

I asked William for help matching a sub to the box. He sent me back a ton of links and info. In one email he more than doubled my subwoofer knowledge.

I will save you from a half-winded explanation of subs, sizing, and other such stuff and just give you the details.

I used a Rockford Fosgate P1S4-8 8″ subwoofer in this box. Mine is the 4 ohm version. It’s sized for a .2 to .3 cubic foot sealed box, so it’s perfect for the Black Roadster footwell box. It’s a 200 Watt RMS speaker, so it needs an amp that puts out something in that neighborhood (so I read).

And the little footwell box and RF sub work very well together. The sub mounted into the box with no problems at all. I highly recommend the pair.

Beefy wiring.

Beefy wiring.

I grabbed this 4 gauge wiring kit from amazon. It’s a “New England Providore” 20 foot 4 gauge kit with RCA and speaker cable. I’d link but at the time of this blog post it’s out of stock.

Decent wiring. Stranded copper with nice rubber insulation. Very easy to bend, crimp, and work with. I’m pretty happy with it.

That's not a phone on the tire, that's my amp.

That’s not a phone on the tire, that’s my amp.

The tiny silver brick on the spare in this shot is my amp. Seriously. THAT tiny thing is a 600W amp! Back in my day, an amp of any power rating was the size of a brief case.

It’s a Kenwood KAC-M3004 amp. 4 channel, 600W max, bridgable. At 4 ohm bridged it puts out 150W per channel. So it’s sized well for my little 200W sub. Or at least that’s what I read and am attempting to blog here.

If you’re interested, google it. There’s a nice youtube of this amp on a dyno putting out some incredible numbers. It’s underrated from the factory. The dyno example put out 730 watts. That’s… insane. This tiny phone sized thing? Yeah. Technology.

Seems like a good place.

Seems like a good place.

I looked all over the trunk and settled on the fuel hose cover as a mounting spot for the little amp. I wanted to put it in the passenger side tunnel, but that seemed a little hard to access. I still might shove it back there, but for now it’s mounted on the fuel hose cover.

Nice thing about mounting it here – I can easily find a replacement cover if I want to remove the system or move the amp. No permanent holes were drilled. It’s not often that I can say that about any given Miata project.

Power and ground wires cut.

Power and ground wires cut.

Wires. I cut them, I crimped them, I mounted them to the car. Nothing much to say about it. I used one of those hammer crimpers for wires above 8 gauge. Just a cheap one from amazon that I ordered with the wiring. It didn’t make the prettiest crimps, but it worked!

Amp mounted.

Amp mounted.

Sub in place.

Sub in place.

I could have probably done a better job making the wires pretty on that amp install. Alas. It’ll give me another Miata project a few months in the future. I need to look at some pretty amp install pix.

The footwell box wedges in there solidly. It does indeed take away foot room. My legs don’t stretch out in the passenger side anymore. But the box also comes out easily and can fit in the trunk for a quick trip with a passenger.

With floor mat installed.

With floor mat installed.

With the floor mats installed the sub just disappears. I love this! Stealthy even if you’re looking dead at it.

Now, the several hundred dollar question: how does it sound?

BOOM!!! BOOOM-wiki-BOOM!!!

It sounds great. The amount of depth this little sub adds to any given song is truly impressive. It’s very clean bass too. I’ve got things tuned to not really distort. It sounds fantastic.

There’s even bass with the top down while driving at freeway speeds. THAT is something you rarely get from a trunk mounted sub. When the top goes down, your bass goes away. But with the footwell sub, your tunes stay rocking.

I’m really impressed by this upgrade. I should have done it a while ago. I just didn’t take the time to think who my passengers usually are. For the next 5 or 6 years, my copilot won’t have a problem with leg room.

If you want to get one of these footwell subwoofers, reach out to William. He’s…
black roadster on ClubRoadster MiataTurbo, MazdaRoadster and other forums.
blackroadster96 on Facebook
blackroadster on Instagram
and can be emailed at blackroadster96 at yahoo dot com.

Thanks for the box, William! And for all the help finding a speaker and amp for it.

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  • William Curran says:


    Great review. I’m very happy you’re so pleased. I tell you, anyone who hears it is impressed this is a single 8″ woofer. Say no to trunk subs!

    I have more boxes I will be finishing next weekend. As this is a side business / hobby for me, they aren’t always available to ship. Contact me for details as Adam mentioned above. I just love sharing proper bass to the Miata masses!

    • Larry Hilker says:

      I can’t get your website,, to work for me. Just comes up blank. I’m also an old guy with old school ways and prefer talking to people. I would really appreciate a phone call as I am very interested in a miatabox for my 1990 Miata which I’ve owned since it’s birth.

      Thanks for your time!

      Larry Hilker
      (828)253-0661 (available from noon to midnight Eastern time)

  • GT-Alex says:

    A good addition to the setup could be the Carbonmiata rear deck panel :

    With regular speakers rather than subs in there that would definitely be a killer setup even for top down duties.

      • revlimiter says:

        I’d actually searched for that one not long ago and couldn’t find the NA one. I could only find the NB. So, thanks!!!

        As for that panel, I agree that it could be a great setup. I’m considering grabbing one and putting it away for the day when my copilot has long legs.

    • Zandr says:

      That panel is designed to be carpeted over, with subs underneath. I wonder how midgranges would sound through the carpet?

      • GT-Alex says:

        Wondering that as well, as that’s what I would need more.

      • Brian says:

        They sound muffled, enough I folded the carpet back to keep them exposed. So the next project was to mount baffles in the carpet and now they sound great. And that is with mids, not subs–3rd Millenium M800s. Vast improvement in sound, even top-down at speed. I’m very happy with how it turned out.

        • Zandr says:

          “…mount baffles in the carpet…”

          I’m having trouble visualizing that. Got any pictures anywhere?


        • GT-Alex says:

          A cut-out or just holes like on the OEM headrests could do the trick maybe ?

        • Brian says:

          I posted a brief writeup with pics on mnet in the audio section. “CarbonMiata rear deck installation”. For a good mid-range sound this route is an awesome alternative, especially if headrest speakers aren’t possible.

  • “Free Air” (infinite baffle) setups generally don’t have the SPL of a sealed box. Another bad thing about using IB is that the subs will be sacrificing the deep bass compared to a properly designed sealed or ported system. There are two basic subwoofer types: suspension dampened and enclosure dampened. Most suspension dampened subs play fine (and even excellent) in enclosures, but enclosure dampened subs wont play free-air well because there is not enough cone control/suspension.

    Infinite baffle set-ups require a woofer with a beefier suspension for high power handling and one with better cone damping. This set-up will be less efficient in reproducing the lowest frequencies as compared to a proper enclosure.

    In any IB application, the back area and surrounding panels should be sealed or energy could be lost. It is crucial to separate (seal) the back wave of the loudspeaker (woofer) from the front wave of the loudspeaker. If not, bass cancellation will occur. This is also a good time to rid and deaden the trunk and surrounding areas of any unwanted noises and rattles.

    In other words, dropping woofers in a panel like that may not be a good solution as far as sound quality. Besides that, its a big flag that says, “Steal me!”

    Trunks subs are a whole other thing. With my box you don’t have rattles. As Adam mentioned, the bass is ALWAYS present whether the tp is up or down and regardless of speed. Speakers work by moving air. How well is a trunk mounted sub moving the air in the Miata’s interior? There is very little space for the air to move between the cabin and trunk. What bass you feel and hear is from the reverberations off the trunk lid and rear deck. This is why it virtually disappears at speed or with the top down. Having the woofer in the interior in a properly sealed box is really the most efficient way to get bass.

    I’ll jump off my foot well sub box now. 🙂

    • GT-Alex says:

      Your box is sure definitely a better design for a subwoofer. I’d go more for mid range speakers with this panel I think, and get some insulation underneath. Stock carpet goes over it, so no stealing problem, but don’t know if that would effect mid range speakers – although some NAs have headrest speakers.

    • Zandr says:

      Yeah, I was looking at that panel as a solution for rear-stage, not a sub. Your box looks like the right answer for my needs, and I’ve already emailed asking to buy one. 🙂

  • It’s been a while. Still enjoying the sub woofer box?

  • mx5 2nr says:

    I’ve been trying to chase the impossible – good bass in a Miata without losing the entire trunk & am seriously pondering this footwell box. I’ve gone through too many “experiments” to list & spent a ridiculous amount of money thus far. One question – what is the mounting depth on this? I need it to fit a sub with a 4-1/8″ depth. Can this be a reality without modifying? I searched for mounting depth, but I didn’t see it. I’m not opposed to modifying it, but if I don’t have to it would push me to break out the credit card…

  • Francisco Sanchez says:


    So anyone have any experience with this in an NC?

  • Cthulhu Yata says:

    Wouldn’t the fact that the sub faces the floor damage the edge of it? And possibly cause a tear on the outer edge of the cone? Recently purchased a trunk box, since i had 2 10’s laying around. But this seems very interesting, and might look into in when i have the funds to buy another woofer lol.

    • K1 says:


      You are right. you should install a grille to shield it. has a link for a $7,99 grille, but I guess any grille designed to your sub will do.
      I’m new to this but looking to order one next week. So pumped!

  • Arbica Mriea says:

    Love how detailed and informative your guide is on installing a footwell subwoofer in a Miata! Your step-by-step instructions make it so clear. Thanks for sharing your expertise!

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