Single-DIN audio system details

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Can you tell me more about these units?

There are four similar single-DIN head units covered in this section:

Number Year Description
1M321999single-DIN non-Bose
4M322000single-DIN non-Bose
1M311999single-DIN Bose
1M372000, 2001single-DIN Bose

The Bose and non-Bose head units look similar. The major difference is that the Bose heads lack internal amplifiers and instead drive an external amp through balanced differential line-level outputs. The Bose systems also use special low-impedance speakers.

The non-Bose head units include an internal 4-channel amp and are also used in other Mazda products, like the Protégé. The amp is rated to 25 Watts peak power at 4 ohms, which is 12 Watts RMS.

The Bose 1M31 model does not have ANY internal amplifiers, and the 1M37 probably does not, either. The Bose system includes a pair of external 100 Watt amplifiers (connected through a balanced line out) to drive the .5-Ohm Bose door speakers and 4-Ohm tweeters. There is a lot more great information, including acoustic measurements, here.

Part Number Description
B02A-66-9N0A1-DIN Cubby
NC20-66-9R0Non-Bose 1M32 Head Unit (until September 1, 1998)
BG1R-66-9R0Non-Bose 4M32 Head Unit (after September 1, 1998)
NC10-66-9R0Bose 1M31 Head Unit (until June 23, 1999)
NC10-66-9R0ABose 1M37 Head Unit (after June 23, 1999)
NC15-66-9D0Casette Deck
NC10-66-92ZABose Power Amp (until November 25, 1999)
NC10-66-92ZBBose Power Amp (after November 25, 1999)
NC10-66-930Power Antenna (until January 13, 1998)
NC10-66-930APower Antenna (from January 13, 1998 to March 23, 1998)
NC10-66-930BPower Antenna (after March 23, 1998)
B05A-66-A30Power Antenna Mast
NC20-66-930Manual Antenna (until March 1, 1998)
NC20-66-930AManual Antenna (after March 1, 1998)
KA03-66-930Manual Antenna Mast
NC25-66-960ANon-Bose Door Speaker
NC18-66-960Bose Door Speaker (until July 1, 1998)
NC18-66-960ABose Door Speaker (from July 1, 1998 to July 31, 1998)
NC18-66-960BBose Door Speaker (after July 31, 1998)
NC18-66-960DBose Door Speaker ('03 Model)
NC12-66-960Door Tweeter

My Bose stereo sounds terrible!

See also Bose Buzz

Most people think the Bose system sounds pretty bad, and after 3 months with my car I tend to agree. With the bass and treble controls set at the default positions, the radio has boomy, poorly-defined bass and too much treble, but no midrange. I set the treble control down two "blocks" and the bass almost all the way down to get halfway decent sound. But it's still boomy sometimes!

Also, there is a known problem with the early ('99) Bose door speakers. They tend to get wet, and when they do, they start to buzz like blown Wal Mart specials. Your dealer will probably install a set of baffles to keep them dry if you complain, or you could order some baffles from a place like Crutchfield or a local car audio shop and put them in yourself. This will help, but some folks like to install some dynamat-like sound dampener in the door panels in addition to help keep the buzzing down further.

If you really hate the Bose system, you can remove it.

How are the speakers wired?

The speakers use a single wire pair from the head unit or Bose amp in the dash through to each of the doors. This is then spliced to provide signal for both the tweeter and door speaker. There is no crossover in the stock setup! Instead, the tweeters contain a capacitor which acts as a frequency limiter. This setup can cause trouble if you plan to replace the speakers and amp and re-use the existing wiring - you would need to put a crossover in the doors! This is something most folks would rather avoid because the Miata doors can be somewhat moist. This post has more information on the topic.

More information and photos are in my door disassembly page.

Can I replace the speakers?

Yes. It's an easy upgrade for the non-Bose systems, and a little harder with the Bose. First, we will talk about which speakers fit, then we can focus on making it work electronically. Parts Express sells a special harness set (Metra 72-9300) that will allow you to connect directly to the main speaker wires in the door with no cutting.

Most 6x8 or 5x7 speakers will fit in the doors, and you can just swap out the old speaker for the new one. 8-inch round components will also fit with some (non-metal) modifications. There is quite a bit of room in the doors, maybe 4 inches of depth! Many folks also use a material like Dynamat to dampen the buzzing and rattling trim inside the doors, but do not surround the speakers with this material entirely or you will dampen the music, too!

For the non-Bose, you can power normal speakers with the head unit, but you will probably want to add an external amplifier, too. If you do, use one with speaker-level inputs if you want to retain the stock head unit because there is no line-level output. Lots of people put a new amp in the [:Image:Trunk.jpg|cavity on the passenger's side of the trunk].

The Bose amp must not be used to drive normal non-Bose speakers since the Bose speakers are a special .5-Ohm type. However, there is now a new solution from Clearwater which includes much better speakers for Bose systems. You can add an aftermarket amp and speakers together, however. See this post for more information or perform a Bose-ectomy.

More information and photos are in my door disassembly page.

I don't have the tweeters, how hard is it to add them?

The Miata is not pre-wired for tweeters if they were not originally installed. And you might not want the pre-wiring anyway - there's no crossover, they are just run in parallel with the door speakers! Instead, the tweeters contain a capacitor which acts as a frequency limiter. It's not too hard to add tweeters, just tap into the positive and negative wires and mount the tweeters in the door panel.

You might also want to add a crossover or "L-Pad" for them. A crossover is a device that limits the frequency going to a speaker, while an L-Pad is a limits the amount of power (and thus sound volume) for a speaker. If you add a tweeter and it is too loud, or is distorting, you should add one or both of these. The tricky part is figuring out where to put a crossover. You can put one in the door, which makes wiring easier but is risky (moisture could get on it). Or you could put it inside the dash which makes it much trickier to run the wires. More information

More information and photos are in my door disassembly page.

Can I replace the Bose amplifier and use the stock head unit?

Yes, but the Bose head unit puts out two balanced, isolated channels. See this post for more information. There are adapters available for this application, too. It is possible to drive the .5-Ohm Bose speakers with an appropriate aftermarket amp, but you will probably want to replace the speakers, too. Or perform a full Bose-ectomy. More Information

Can I replace the head unit?

Yes, and it's easy, too, for the non-Bose system. Just buy a wiring kit with your new head unit and go to town. Here's some information, and here's some more. Here's another great thread.

If you have a Bose system, it's a little more tricky. Most people bypass the Bose amps and replace the speakers when doing this, effectively removing the entire OEM sound system. But you can also use an adapter and keep the Bose amps and speakers. There are three choices of adapters:

Part Price Notes
Scosche OEA-4$49.99
Peripheral Vendetta 2.5$31.95
Audio Control Overdrive$99.99OVERDRIVE Pre-Amp Line Driver
Up to 24dB of Signal Gain
High-headroom PWM Switching Power Supply
13 Volts Peak Output Signal Level
Balanced Differential Inputs and Outputs
2v, 5v, and 7.5volt Output Signal Level Indicator LEDs
Capable of Driving High Capacitance Cable Loads

I want to bypass the Bose system entirely. How do I perform a Bose-ectomy?

Let's say you want to replace the head unit, Bose amps, and Bose speakers but want to keep the stock wiring to make everything go in easier. Here's what you need to do for a single-DIN (1M31/1M37) Bose system in a '99-'01 car. more info Bose to double-DIN upgrade

  1. Pull out the head unit, disconnect the harness and antenna.
  2. Disconnect the Bose amps (below/behind the heater controls inside the dash). It's easier to leave the amps in place since it's nearly impossible to remove them! You can disconnect them by reaching under the panel on the driver's side (see this picture). I found it easier to remove the plate under the steering wheel and reach in over the panel (see this picture). You then need to jumper the pins together according to the table below to bypass this connector. If you want to remove the amps, you're supposed to remove the dash! But you really don't have to. Just remove the HVAC controls and radio and you will see the bolts holding the amps in. Then bend/remove the flanges on the plate holding the amps in and it can be pushed out through the passenger footwell.
  3. Undo the door trim and remove the Bose speakers from the doors (you can leave the tweeters since they're normal 4-Ohm units).
  4. Sell the head unit, amps, and speakers to some sucker on eBay.
  5. Buy a Metra 70-7901 (from or Parts Express*) or a Scosche MA02 and wire it to the harness that came with your new head unit according to the pinouts listed below.
  6. If you are adding an amp (optional) mount it under the dash or in the trunk (see this picture) and then splice your inputs and outputs according to the table in the audio pinout page.
  7. If you are not adding an amp, just splice the Old Amp Input and Output together.
  8. Install your new speakers in the doors, using the Green wire for positive (+) and the Yellow/Green wire for negative (-). If you don't have green and yellow green, then look at the table above and match them up accordingly.

Can I add rear/windblocker speakers?

Yes, see this thread. Here is some more information about adding windblocker speakers. Here's a writeup on adding headrest speakers to the '01+ "surfboard seats" with the 4M32 head unit.

The 1M32 has a switch on the bottom of the head unit in the back that changes it from 2 to 4 channels and enables the fader feature. You must unplug the unit entirely before flipping the switch, or the change will not be registered by the head unit.

The 4M32 looks similar to the 1M32, but does not have the switch to enable 4-channel mode. Instead, just press "Audio" for 5 seconds and 4-channel mode will be enabled. There is a page of information available about this unit. If you are installing this unit in another vehicle, this post has more information. And this post gives details on installing it in an NA as does this one.

The 1M31 (Bose) model does not have the rear speaker capabilities. The 1M37 probably does not either. So the only way to do this is to replace the Bose amplifier with an amp capable of driving 4 speakers.

The 2004 factory windblocker with speakers might look like a tempting choice, but it's not really a reasonable one at this point. Other Miata.Netters have looked into it, and found them very expensive. The standard windblocker with speakers costs $687.05, while the Bose one costs $1236.45. Street price is somewhat cheaper, but not enough to make it competative with a decent aftermarket setup. Also, they're just 2" speakers, nothing special.

Which wiring harness do I need?

Metra makes a pair of two-connector sets (sold by or Parts Express*):

  • 70-7901 plugs into the car's harness.
  • 71-7901 plugs into the head unit's socket.

Scosche also makes a connector:

  • MA02 plugs into the car's harness.
  • MA02R plugs into the head unit.

What is the pinout for the wiring harness?

The single-DIN units use an entirely different set of connectors than the double-DIN units. This head unit has three connectors on the back. From left to right (looking at the back) are: CN200 (the casette connector), CN701 (the main harness connector), and CN702 (the rear speaker connector). More information is available at Miata.Net.

Pinouts are available in a separate document:

CN701 (Main Harness) CN702 (Rear Speaker Connector) CN200 (Casette/CD Changer Connector) Bose Amplifier Connector

Can I add a CD Changer?

Yes, you can use an OEM changer or buy an MAZAS adapter for an Alpine M-Bus changer. Both use the CN200 connector on the head unit or can daisy-chain with the tape deck.

Can I add a casette deck (or remove the one I have)?

Yes, the Mazda in-dash casette deck (part number NC75-79-9D0) works fine with all. The retail price is $215, but Trussville Mazda charges $168. It's fairly easy to install, but requires removing your head unit.

If you don't like having a casette deck, you can install a storage box (part number B02A-66-9M0A) in its place. MSRP $11.15.

Can I add an Auxiliary Input?

Surprisingly, this is also a simple mod! Look here (note that right and left are reversed on this page), here or especially here for more information. Here's a nice iPod install. Note that the pins you will need to tap just happen to fit the power/hard drive LED/speaker/keylock connectors used to connect PC motherboards to cases. Dig up an old computer case and cut off the female pigtails, and use these instead of trying to solder to the pins directly.

My CD player just spits out any CD I insert

There's a nice thread on Miata.Net about fixing this.

How do I set the clock?

Press and hold the clock button for about two seconds. The clock will flash. Use the up arrow to set the hour and the down arrow to set the minute. Press CLOCK again to commit the change.

Can use this head unit in some other car?

You can easily use the non-Bose (1M32 and 4M32) in other cars, but the Bose (1M31 and 1M37) are almost useless without their amps and speakers. Of course, any halfway-decent aftermarket unit is going to be quite a bit better in terms of sound quality, but you might want to match your car's interior or something.

The non-Bose units have about 25 Watts per channel over four channels, and should fit in any standard-sized DIN slot in any car. If you have a recent (but older than 2001 or thereabouts) Mazda vehicle, the harness in your car should be a direct match for the head unit. Specifically, NA Miatas should match fine, though their supposed DIN opening is a little narrow. Otherwise, buy a Metra 71-7901 from Parts Express* or a Scosche MA02R and wire up the head unit to match your car's harness.

Do not bother with the Bose (1M31/1M37) head units unless you already have a Miata with the Bose amps and speakers. It would take way too much effort to get it to work.

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