My 1997 Miata Stereo System

Back Home.

There were three concerns involving audio in my Miata.

The First was space. Space is at a premium with this car, and I could not afford to fill the trunk with all sorts of equipment. I will go as far as to mount my spare tire underneath the car, but I would've done this anyway in order to fit 2 sets of golf clubs in the trunk. Every component I looked at had to fit, or be of a small enough size to fit the car.

Second was Bass. You've probably asked yourself, 'How can I get more bass in this car?'. I am by no means an audiophile, or bass booming rap listening, house vibrating bassophile. But the car desperately needed some bass. Every speaker purchased had the lowest range in it's frequency response range I could find.

Third is security. The Miata is a convertible, I wanted a good sounding system without worrying about anyone stealing any of my stereo equipment. Therefore, the headunit is, and will stay factory. Everything about my system is designed to be hidden.

Headrest Speakers
1998

Component Door Speakers
2001

Amplifiers & Crossovers
2001

Schematic of my Stereo System

Custom Rear Deck Subwoofer Box
2002

Subwoofer Box 'Plans'

Sony 10 Disc RF Modulated CD Changer
2002

Other Sub Box Plans

Auxiliary In Jack
2003

Recent Changes

Headrest Speakers

The headrest speakers are a nice addition to a system, but not really required. They're simply too small to get any decent low tones. I use mine as a mid fill, at very low levels compared to the other speakers in my system.

I am debating removing them from my system, as it could give me more room in the trunk* to add a CD changer.

*By removing the headrest speakers, I would have no need for the small Jensen amp and crossover.

Don't expect any bass!
They really enhance the music alot.. And while they sound much better than factory headrest speakers, they can still give you a blinding headache after a half hour of listening to them at a loud level.

The infinity kappa 3.5" speakers blow most speakers this size away. They definitely make the factory headrest speakers sound like a pair of cans and string! I'm not going to tell you how to install them.. I will tell you a few things I found however..

Solder all the connections to the speakers..
Its a tight fit, and slip on connectors will give way sooner or later.. You will have to play with the speakers a bit to fit them in well.. The leads shouldn't end up with pressure on them (From the foam surrounding) and the foam sides should give way a little to accommodate the speaker.. In each headrest, the speakers fan out a bit.. In other words, the speakers don't shoot straight ahead, the right is aimed slightly to the right, and the left speaker is aimed slightly to the left. This is more for fitting purposes, and I don't have a clue what the effects are acoustically.

You don't have to cut your existing speaker foam headrest backing...
What I found, was that removing the front hard plastic speaker covers (Which probably muffled the sound to begin with) and replacing them with a thin foam layer worked very well. They fit very snug, and as you can see from the photo on the left, the headrest is not bulky, or protruding. The foam I used was packing foam found in most computer accessories boxes. The grey or black type foam that ranges in thickness about 1/4" - 1/2", and don't get any 'carpet buzz' from them. I used 1/4" stuff, & to be quite honest, I've never rested my head on a car seat while driving yet. I couldn't tell you if its comfortable to the back of your head or not.

Doesn't look like much does it...

...That was the point.

Tweeter Location behind the door panel.

I've seen others mount tweeter's in the eyeball vents in the dash.

Door Speakers

Kenwood KFC-P703's.
These are Kenwood Component speakers that give great quality sound. I bought these for two reasons;

First, the woofer's have a low end frequency response of 30Hz, which was the lowest I could find. And second, the tweeters gave the widest range of installation possibilities (flush, swivel, etc.)

The KFC-P703's are 'oversized' 6 3/4", and offer a low freq. resp. of 30Hz. They fit like a glove. You only need to mark/drill 2 hole in the speaker face frame to match up the 3 OEM mounting holes in the miata door. I had originally installed KFC-P603's (6 1/2") components (Long story I won't get into) and these 703's add just a hint more bass, really rounding out the sound imaging.

The woofer install is pretty straight forward, Drilled 2 holes in the speaker face frame to match up the existing mounting holes/screws in the miata door. I also added waterproof baffles.

The included crossover is installed underneath the dash, with both sets of wires (for the tweeters & woofers) running through the door channel wiring harness.

The tweeters were quite scary indeed. All I can say is measure 100 times, and cut once. I MAYBE could have got the tweeters to install as swivel mount, if I had moved them a bit more forward, but I doubt it.

I wound up mounting them as fixed (using pieces from the various fixed & swivel options), and angled them to their desired position, fixing them in place with a dab of hot glue which did the trick. Otherwise the flush mounting rings & brackets were just a little too large, and there was alot of pressure on them. Cutting down the depth of the mounting ring, and hot gluing it in place did the trick.

The woofers do come with grills, but I opted to hide mine behind the plain OEM door grill for security reasons.

Once installed, the tweeters seemed a bit overpowering, but they were quickly subdued with the addition of the subwoofer box (below)

If I had to choose any stereo modification that gave the most bang for the buck, it'd be this one. The sound is great, and despite the tweeters, there is nothing screaming 'Steal Me!' to thieves.

The tweeters can be a bit annoying if you don't position/listen to them first. These were installed in a fixed position, so you would want to be sure they sounded perfect prior to final installation.

Custom Subwoofer
For my 1997 Miata

This was by far the most fun of any of the Mods I've done to date, as it entailed building a custom box to fit on the rear deck, which houses 2 Rockord Fosgate punch 8" subs (requiring a minimum of 3 cu. ft. space each).

I tried countless ways of designing a box with the most cu. ft, hoping to port it (which just didn't happen). There is room beneath the rear deck on each side, but by the time you fit the 'walls' of your box in those spaces, you wind up with not much room at all, and a box which is not very structurally sound. I thought about creating a custom fiberglass enclosure to solve that problem, but after reading about vibration & bracing concerns associated with fiberglass enclosures, I chose to build the box to fit on top of the decklid, from 1/2" MDF. The box weighs about 20 lbs with the subs in it, and is very sturdy due to the bracing.

The top folds down (with the box in place) rather snug. I rounded the back edges and back corners of the box as much as possible (By sanding with 60 grit sandpaper), avoiding any tearing or denting of the plastic window. You cannot put the tonneau cover on with the box installed. The window folds up and over the box (Which is slanted at both front and back) and does not crease, dent or fold. I recommend folding (or 'pushing') the window down and back into the rear package tray recess after unzipping it, but before lowering the top. This will insure that the window portion of the top doesn't 'stretch' over the corners of the box as the top is lowered.

The box has a 'stair step' in it, allowing the cross bar/brace to tuck neatly and hold down the box. Initially I had built the box without this recess, but later I went back and cut one in because the brace was putting too much pressure on the box.

I did not add any polyfill to the interior of the box, as it did not give me the punch at low end bass I expected.

The best part: The bass is awesome. I run my system with just about half front/half rear fading, and the car booms enough to give me great bass at any volume! While I don't listen to much rap, this box could certainly handle it. But don't expect to thump your neighbors! This box is only .65 cubic ft total, so your not going to be blasting a 12" sub with 300 watts through it. I'm not sure how th ebox would hold up to a large single subwoofer, since elimination of the center brace would make the box less sturdy.

Want to build your own?
Check out the DESIGN here.

Custom rear deck Subwoofer, with the top down.

Custom rear deck Subwoofer, with the top up.

The worst part: I originally built this box as a trapezoid with no stair step in it. I went back and cut my stairstep into the finished box, as I wasn't happy with how tight the crossbar was on top of the box. While you could probably tork down on the crossbar alot, I opted to cut away the rubber surround on the crossbar to give me a little more room. I found that I could not get the crossbar seated all the way without the box cracking and popping, so I trimmed away the bottom 1/3rd or so of the rubber surround on the crossbar using a utility knife on each side, and then prying/peeling the rubber up. The bar inside is round and not flat like I had hoped, but it did give me another 1/4" or so of height to squeeze the box into. After all was said and done, I noticed that on a buddies 93 M edition he didn't have a crossbar at all... Kinda makes me wish I had just removed the thing and just left the box a trapezoid instead. Too late now though. You also can no longer make much use of the rear decklid for 'storage'. No biggie here though, as I never used it much to begin with.

I also originally built this box 14" deep. After 3 months I noticed some minor wear on my soft top at the seam nearest the window. I've been recommending 13" depth instead, which apparantly allows for the top to seat all the way down properly, and helps to eliminate any soft top wear. (See the plans below)

Nitty Gritty: Hows it sound? Pretty damn good. It'd probably sound better if I had more cu. ft. to work with, but the bass is a nice addition to the sound stage. Because it is down firing, the bass is not dramatically delivered behind you. It sort of resonates around you, while being just mildly aware that it is behind you. I think the headrest speakers (highs) help balance the bass out a bit also. The rockford's I used are ok, but really bottom line subs that tend to sound a bit flat at low Hz. I didn't want to blow alot of money on subs if the box didn't work well, so I may upgrade in the future. Most subs (even the small 8") have a pretty deep top mount depth, so I would check that before you decide on purchasing, especially if you want to keep the cross bar brace.

Amplifiers, Crossovers

Everything fits nice and snug in the trunk center well. All pieces are mounted to a 1/4" piece of plywood (painted black). Cables are held in place with strips of velcro, attaching them directly to the carpet lining in the center well.

The Profile Clarus amp (Top center) drives the front components, as well as the subwoofers.

The small cheap Jensen amp (Low left) drives the headrest speakers (wired in parallel), and is not very powerful (only 25W RMS) but it doesn't have to be. The headrests are only 35w speakers.

There is an electronic crossover (Lower right) which helped me solve the problem of keeping the headrests in the system.

There are also 3 supports made from '1 by' pine. These supports hold the cover in place.

The photo showing the cover in place doesn't have the spare tire because I wanted you to see the wiring/entire cover. The spare tire does in fact fit and screw down without any problems (Unless you add a cd changer like I did). The spare tire covers part of the amp cover when installed.

I used Gutter Guard aluminum screening (stapled) and 3" computer cable grommets (cut down to 1'2" high and hot glued into place) to create the vent holes in the lid.

The grey carpeting is a close match (But not exact) to the oem trunk carpeting, and was purchased from JC Whitney. They give you enough carpet to redo the entire trunk base if desired.

I've used the extra carpet over the rest of the floor of the trunk so that the cover matches more closely. It also allowed me to run carpet up into the tunnel, and cover the right side shock mount area as well. Now the carpet isn't as noticeably different because the change occurs where the side carpet meets the floor carpet.

The Amps & Crossover in the trunk.

Everything covered up.

FYI if you haven't done it already, I'd recommend disconnecting the trunk latch cable so thieves can't get to your trunk by slashing the top and using the lever in the center console. Be sure you loop the cable back and secure it. The first time I disconnected it, I left the cable hanging. A few weeks later, to my suprise, it had found it's way back to the trunk latch mechanism, so I had to disconnect it again. I've also NEVER locked my car (or left anything valuable in it). I've had at least one person enter the car (while parked overnight at the airport), but nothing was taken. Some thieves may just slash without trying to open the door though.

All the components of my stereo system

All components were purchased through Crutchfield or Ebay. Pricing may not reflect todays prices.

The overall cost was about $1100, not including any labor or time in installation or box building.

You could cut the cost and installation time down by not including the headrest speakers. This would eliminate the need for the crossover, headrest speakers and jensen amp (about $200 worth)

The crossover does help by splitting the signal prior to the amps. By splitting the signal before the amp, each amp gets 100% of the frequency's I want, eliminating the need to discard signal by using the built in crossovers on the amp itself.

On my setup, I noticed alot of bass to the right side. This was repaired by setting the line outputs at low levels (about 1/4 of ull output), and letting the amps do their work.

NITTY GRITTY:
The Front Door Speakers (50W RMS) are powered (50W RMS) by the Profile Clarus Amp.
The Subwoofer speakers (4 ohm, 100W RMS) are wired in series to the bridged mono (Ch 3 & 4) Profile Clarus Amp Producing 75W RMS.
8 ohm subs would've allowed me to wire these in parallel to the bridged mono (Note the profile clarus req. minimum impedance of 4 ohm in bridged mode), but the amp would run hotter.
The Headrest speakers (30W RMS) are wired in parallel (for each L & R channels for both seats) to the el cheapo Jensen Amp producing 25W RMS to each headrest speaker.
Power & ground is provided via 10 g. wire at around 3 feet total length.
Accessory power is provided to the amps and crossover from the headunit (spliced) because I ran into problems providing multiple accesory 12v from the power antenna connector (used for accesory on the CD Changer instead)

Subwoofer Plans
(for my 1997 Miata Rear Deck Lid)

PLANS CHANGED AS OF 7/17/2002
This was alot of work, and I'm not going to give you intricate instructions. But I will provide you with dimensions on the finished box, as well as little tidbits that I found helpful when creating this piece.

Materials:
1/2" MDF (medium density fiberboard)
Black Subwoofer box carpeting (Crutchfield)
1 1/4" Drywall screws
Wood glue or construction adhesive
3/4" material for 'feet'
1/2" x 3 1/4" x 38 3/8" pine (Stairstep)
Scraps of pine material (Bracing)
2 - 8" (or smaller) subs requiring min. 3 cu. ft each

Dimensions - The box should not be longer than 39 3/8", wider than 13" and taller than 5" at the top of the stairstep (To fit under the crossbar brace). Once assembled and carpeted, it will be a tight squeeze between the seatbelt posts. Note that you will need to remove the rearmost tonneau snap bolts in both of the seat belt post covers in order to install the box. If you do not want to remove these bolts, you will need to measure between the 2 bolts and subtract 1/8" or more from the total length available.

Mounting - I did NOT bolt or otherwise screw the box into the rear deck in any way. It is sandwiched between the seatbelt posts, and the cross brace pins it down into position in the 'Stairstep' located at the front of the box top. I do plan to attach the box to the car somehow in the future. If and When I find a way to do it, I will post the information here.

Cubic ft. - It is important to note that the box shown above, will give you roughly .325 cubic ft in each side (or .65 cubic ft total), which doesn't include speaker displacement (the Rockfords I put in were .02 cu.ft. each) but does include internal bracing. Be sure to use a subwoofer which can be used in this small space. You could opt for a larger single subwoofer (Providing it will fit) and then have .6 cubic ft to work with, but you'll need to consider putting braces (pehaps like the center brace but with a large hole cut in it) on either side of the single sub. This will help eliminate any flexing in the box. Remember, it's only 1/2" mdf.

Feet - I recommend using 3/4" rubber material ( at each corner and in the center to keep the box raised and allow the sound to eminate from the bottom of the box without getting muffled in the carpet. Any smaller (Than the 3/4" height) and the subwoofer faces will be pressed into the carpeting on the rear deck. I used furniture 'cups' originally intended for use on furniture feet/floor protectors, which I found to be 3/4" height and constructed of rubber.

Rear Deck - The rear deck has a layer of rubber and insulation padding underneath the carpet. You can always remove these if desired, to give you a little more height to work with. But I preferred to leave the padding and rubber in to help eliminate any rattles. I swapped my insulation with 8 lb. carpet padding & I also added some foam insulation strips underneath and around the bolts which hold down the aluminum deck cover to eliminate any rattles.

Use Some Pine - I would recommend using pine (or some other wood besides mdf) for your bracing, and 'stair step' piece (And possibly even the endpieces even though I didn't) as the screws will hold better and not strip out when screwing all the pieces together.

Round the Corners - Round down all of your corners and edges as much as possible (Power sander works well) at each end of the box to help avoid any sharp corners against your soft top.

CHECK OUT OTHER REAR DECK SUBWOOFER ENCLOSURES PEOPLE HAVE EMAILED ME ABOUT, AS WELL AS A NEW MODIFIED 14" BOX BY CLICKING HERE OR SCROLLING DOWN TO THE BOTTOM OF THE PAGE.

SIDE VIEW BOX PLAN

RECOMMEND GOING WITH 13" WIDTH (Instead of 14" as previously designed) as some minor wear appeared on my soft top with the 14" box after about 4 months of use. I've test- fitted this new design (By temporarily positioning my current box forward) which seems to solve the problem quite well, allowing the top to now lower completely.
UPDATE: I built my new 13" box back in the spring of 2003 and have not encountered any additional problems with the soft top in the 2 years since then.

The front and rear angles of the box are different. 31 degree cuts for the front, to match the 59 degree incline of the rear 'firewall' leading up to the decklid, and 39 degree cuts for the back, to get the most angle you can while trying to keep within the .3 cubic ft limit, and allow the window to fold over it.

Putting it all together - wasn't as bad as I had originally thought. Though countersinking all the screws was a painstaking experience. I started with the top of the box (Piece C), screwing and glueing each endpiece onto it. Then I worked my way around all sides and braces, except for the bottom face (Piece D) which I temporarily screwed into place but didn't glue. I then strap clamped everything and let it sit overnight. The following day, I removed the face to silicone all the cracks and crevices, & test fitted. Once I got my speaker leads and everything in place, I then glued the bottom piece on using construction adhesive and screwed it into the bracing.

Silicon - Your friend and mine. I used ALOT of it. I goopuckeyed every seam and crack I could get to to ensure the box was airtight.

The carpet - (Black carpet from crutchfield) was applied using some spray adhesive and staples. I first attached the side pieces of carpet, and then 'wrapped' a piece of carpet from the back bottom, and over the top to the front bottom. I stapled the carpet to the box on the bottom face because, noone will ever see that side anyways. The wiring was then ran underneath the box to the passenger side of the rear deck, under the rear deck carpet and through an existing triangular opening into the trunk.

Installation - The easiest way to install it is to first remove the cross bar brace, and then slide the box into position (With the canvas top raised). Then lower the canvas top and put the crossbar brace back on while keeping the box forward & 'snug' up against the brace when tightening the hold down bolts.

If you make your own box based on this design, let me know about it. I'm sure plenty of people out there could come up with some pretty good modifications to this design.

I originally built this box as 14" deep, but noticed some minor wear on the vertical seam (nearest the window) after about 3 months. I had been recommending 13" depth to anyone inquiring about the box, and have since updated my plans to reflect this change.

DISCLAIMER: I created this box on April 13, 2002. The rear plexi window seems to be holding up well, and doesn't appear to be affected by the box, but only time will tell. As of July 17, I have noticed some minor wear on the vertical seam (nearest the window) on the soft top. I recommend building the box at 13" in width, instead of 14" to help eliminate this risk. Current Illustrations/plans reflect this change.
Perform this mod at your own risk! I cannot guarantee the box will fit other years, but it should fit all 90-97's without any problems. Miata's without a crossbar brace should be able to accomodate a box without a stairstep cut into it. This box design will probably not fit miata's with roll bars installed. It has also not been tested on miata's with GLASS rear windows. This box design has NOT been tested with a hardtop either. The plexi window will not go as low into the cabin with the box the same amount as without the box. This may affect the hardtop. I do have a buddy with a hardtop though (my old one actually) so I will test it soon enough and let you know the results. Double check all your measurements and test fit throughout the entire building process.

Please do not email me asking for directions on how to build this box. There is plenty of information here for an adequate woodworker to understand and use to build their own. If you cannot determine how to build the box from the information given here, then hand the design over to someone who does.

The CD Changer mounted to the trunk/tunnel.

I chose to mount the changer in the area where the spare tire would reside. Time to get the spare tire relocation mod done! (Which I was gonna do anyways). The floor of the trunk is now lined with grey carpet which covers the wiring shown in the above photo.

You can mount the wired remote anywhere really, but I chose cut a slot in the back of my lower compartment and fed the remote up through it. (I cut the slot because if I want to move it later, I won't have to pull the jack from the cd player and rip everything out the get the cable out through the compartment.) The remote is a rectangle with a bit of a 'circle' shape on one end. I cut a notch in the back bottom of the compartment to accomodate this circular portion of the remote. The remote is now mounted against the back of the compartment with velcro tabs. The remote covers the slot I had cut in the back of the compartment, and can be pulled out if needed for operation (Leave enough slack wire in the radio compartment for removing). It's a bit difficult to see while driving (good for stealth, and no wires hangin out) but nothing a little memorization can handle. The button's are intuitive, and very easy to use without having to see them.

The remote remembers if it was on previously, as well as which disc/track it was playing. So if you shut off your car and turn it back on, it picks right back up where it left off. Because it's accesory power is wired to the antenna power, the unit will shutoff autoatically if I shut off the radio or use the cassette player. Whenever I turn the AM/FM back on, it will power on and resume playing where it left off.

One other note, is that if you have the unit turned on, but your radio is tuned to another station, you will not get very good reception, if any at all. However, it is doubtful that anyone would want to keep the cd changer turned on, if you were listening to a separate radio station and not the cd changer anyways.

CD Changer

Sony X454RF 10 Disc CD Changer
I wanted to be able to play CD's with decent sound, and my previous portable cd player with a cassette tape adapter just wasn't cutting it anymore. I was hesitant about getting an RF Modulated CD Player (Connects to any FM Radio head unit through the antenna) as I have heard mixed reports on the fidelity of such changers. But I really want to keep my system stealth looking, requiring my keeping the factory head unit.

After listening to a few friends RF CD Changers, I decided to bite the bullet and buy one. I chose the Sony, because anything I've ever owned in the past from Sony has sounded great.

The result? Awesome. This cd changer has 5 levels of output, so you can control the amount of distortion you might get (if any) by backing off on the output. (I have had no problems with distortion at full volume and full output however) It also has a DBASS function which dramatically boosts the bass. There are 3 levels. You also get a wide choice of stations to set the rf modulator, allowing you to get the best 'reception' from the antenna cable. All of these controls are accessible from the wired remote.

Installation took me about 3 hours, but probably 1 hour was spent trying to figure out where I wanted to put the damn thing. I routed the cable for the wired remote, and antenna cable under the dash on the driver side, along the side of the floor under the sill moulding, and up through the tunnel into the trunk on the passenger side. I brought the cables into the trunk cabin through the right hand lower side of the aluminum plate/cover housing the gas line and vent. (I will cut my extra grey carpet to line the entire trunk floor soon, which should cover all wiring). I ran my power down into the center well and tapped into one of my distribution blocks, and ran the ground to the hold down bolt on the battery bracket. Since this unit would never be used without the AM/FM being turned on, I ran the Accessory power to the radio antenna power in the trunk.

The hard part was mounting the thing. I wanted it raised to clear the other cables/wiring leading to the center well. I also wanted to add carpet to the entire trunk floor, and into the tunnel. I didn't want to add any holes to the floor of the trunk. The mounting brackets (when attached to the cd changer) are spaced so that you can mount them in the recesses on the decklid top. I could have moved it more to the right side (n the photo), but I wanted to make sure I could get holes drilled into the decklid, and remove/tighten bolts while mounting, so I left a bit of a gap on the right side to be safe. I made a pattern on a piece of paper, for the 4 holes needed, from the cd changer with the mounting brackets in place. I then positioned the changer and paper (Taped in place) where I wanted to mount it, and marked reference items on the trunk top (an existing hole, the recesses, etc). Then I marked the other side of the paper (Tracing the marks while held up to a light) so that I could lay the pattern down into position from inside the cabin. Making sure all my reference marks lined up, I then drilled through the decklid. (Um, if you haven't figure it out yet, you need to remove the insulation and rubber pad, and lift the carpet on the rear decklid first. Don't go drilling through your carpet!)

I barely got a drill in there, but I managed to drill the holes from inside the cabin with the top raised. Then I put 4 bolts down through the holes with washers. I then carefully fed each bolt through the mounting holes on the cd changer brackets (already on the cd changer) from inside the trunk. I did this myself, and wound up using a 4x4 inside the cabin to hold/pin down the bolts. But you'd be better off having someone help you hold the bolts down while you feed the changer mounting brackets up into them. Otherwise the bolts want to keep pushing up into the cabin. But if you're on your own, then just start each bolt separately, getting a locking washer on and the nut to catch on the bolt, and then move to the next one without tightening. This gave me room to maneuver the mounting brackets while feeding the other bolts through. Once completed, I then went back and tightened all the nuts. wallah.

One dissapointment I had, is that this brand of changer can ONLY be used with the RF Modulator. You CANNOT connect this cd changer to a sony headunit directly. Which kind of bummed me out, because if I ever wanted to get a sony headunit then I would not be able to take advantage of the direct feed connection.

Also - With the rear deck subwoofer I built, the cd cartridge rattles inside the cd changer if I have the volume cranked. It doesn't affect play, as it's the other 9 cd's in their trays which are rattling. SOLVED: On top of the deck, I used a piece of 'sticky' felt, then a rubber washer, then a steel washer (followed by the bolt of course). Underside, I again used a square of felt between the changer mounting brackets and the rear decklid surface. This (Combined with rubber feet on the subwoofer) has drastically improved the '9 free-disc vibration' problems.

To the right is a modified version of my original 14" box design. It overhangs the rear 'firewall' incline slighly (about 1") which is just enough to touch the seats and transfer a little vibration to the driver and/or passenger if you're into that sort of thing. The important part of any rear decklid box design, is that the distance from the rear of the crossbar brace to the rear of the box be no greater than 8 1/4". This assuming that you are using a 39 degree incline for the backwall of the box. This will insure that the top does not interfere with the rear of the box, and will seat fully, when the top is put down.

You can build your box taller, or more forward if so desired. You could even remove the crossbar brace entirely if so desired. (Note that while pre-94's did not come with a crossbar brace, I would not recommend removing the brace, which was designed for cabin stability.)

Other Sub Box Plans

Other people have written about boxes they've built, based on the basic subwoofer box design above. These are their ideas and/or plans...

Adam MacBlane built a box to hold a single 10" sub and says it gives incredible bass. He went 13.5" wide, and 1/2" taller in height, building the box out of 3/4" mdf with no internal bracing.

Mike (aka 'Lordblackrose') already has 2 12" subs in a custom enclosure filling his entire trunk for competition. He's now building an additional sub box for the rear deck, adding 2 8" subs to his current setup for a little more punch!

Modified 14" box design.

This is a modified version of the 13" box design. It utilizes a 14" width for the face (bottom) and 4 1/2" x 1/2" pine (under crossbar brace). It also overhangs the rear inclined 'firewall' by about an inch.

The Basics: An On/Off switch (Single Pole Single Throw) is used to turn on the 'Auxiliary In Jack' by sending power to the Aux Control In (Pin 11). 12K Ohm resistance is recommended, but some have not included any resistance with success.

An Audio Control (Volume knob) is highly recommended to control incoming audio signals. Primarily a safety precaution, its purpose here is to keep incoming audio signal levels down.

Input type is up to you. The schematic here shows a closed circuit 1/8" stereo jack, with optional RCA jacks. This allows you to have a device plugged in using the RCA jacks, while allowing you to bypass those connections when using the stereo jack.

Dont forget to connect the RCA - (GND's) to pin 1

Auxiliary In Jack

Recently a couple of us on Miata.Net forums figured out how to create an Auxiliary In jack for the OEM Stereo (See the thread here).

Auxiliary In Jack Schematic (Click to enlarge)

The biggest problem is getting connectors to fit the back of the headunit. I used small pin connectors commonly found inside computer cases for connections to the front panel computer lights and switches. These fit snugly onto the pins in the 16pin connector, but must be individually connected unless you can come up with a way to make them all into one plug/unit.

Input voltage should not be spliced in from the cigarette lighter power, as a few have experienced problems with alternator whine when doing so.

There is also a 10K Audio Control with SPST rated 3amp 30V available from Radio Shack (Part #271-215) that could possibly be used to combine both the Switch and the volume control knob into one unit.

My tablesaw / workbench is quite cluttered at the moment with test sub boxes & misc stereo equipment.

Recent Changes

SubWoofer Design: I recently built 2 sub boxes to perform some testing. One box contained a single 8" enclosed. Another, with a Single 8" ported. After comparing these with my current 2 - 8" enclosed design, I opted for the single 8" ported design using a Kenwood KFC-W2005 Sub and a little polyfill. Going with the single 8" sub allows me to bridge my amp to 150W.

Clarion Headunit: I picked up a clarion CD player Headunit with Sirius Satellite radio. Haven't hooked up the sirius, but it sounds great. Basically it boils down to alot less parts and better sound, providing my top doesnt get slashed.