http://www.caraudio.demon.co.uk/index.htm

www.caraudiodirect.com

http://www.incarexpress.co.uk/

www.bluespot.co.uk - Blaupunkt at discounts

www.clarionworld.co.uk – Clarion at discounts

1. Halfords do one; look for Mazda one .. Part code PC2-36-6, Item code 675629 (this was 6/99)
2. Maplins is Part No: MZ71, and is supposed to fit all models from 89. Certainly fits ‘92. The cost is about £10.00 including the VAT. The telephone number for Maplin is (01702) 554000.
3. Crutchfield sells a single-din factory look installation kit and plug to fit std wiring for around 17GBP (176MZ8C installation kit $15.00, 095CR18 antenna adapter $3.00, 120707901 wiring harness $9.00, 0000330032 Master Sheet instructions FREE with purchase, Shipping is only $3.95 for express delivery of orders totalling under $100.00 http://www.crutchfield.com/orderform.html

(Info from www.miata.net/garage/audio.html except 1/ which is UK info)

1. Coin/tray type filler = Australian conversion The invoice shows part number HE2155235 00 but the part itself has p/no HE2190235 moulded into the back. By the way, price was 26.73+VAT. They had to order it but it only took two days. ..... 1 1/2 DIN oddment tray, which fits underneath. it's correct name is an 'ornament tuner'
2. 0000-81-0147-1 is reputedly a single (one) DIN euro spec panel
3. B092-55-235B is reputedly a 0.5 DIN x 2" deep panel from a Mazda 323
4. LA03-55-235A = 0.5 DIN filler
5. FC02-55-235A = 1.5 DIN filler, can be cut down to a 1 DIN filler, used on ’90 Miatas only
6. see http://www.seriousauto.com/bezel.htm for surround (double DIN) and ISO wiring kit
7. NA92-55-231 94 MX5 Audio Panel. Note that this panel already has some cut-outs in it, for electric mirror switches

1. Single DIN UK radio with filler panel
2. Double DIN UK radio
3. Eunos/Japan radio with dongle – with or without factory CD
4. Miata/US radio – full FM and anti-theft number code – with or without factory CD

http://indigo.ie/~menzikov/digicombandexpander.htm in Ireland 23.99IRP + Postage

Pioneer TS-E2090. This speaker is a 3-way speaker with a 20 cm (8") diaphragm, the pair of 2090 is effectively a pair of 8" subs. 17cm for doors; http://www.pioneer-eur.com/products/car/ts-26en.htm

www.robpickering.co.uk shows Sony 10cm speakers fitted

http://www.wenet.net/~jaimev/M-hrspeakers/index.html is Head rest speakers install

"JBL GTO402s e-v-e-n-t-u-a-l-l-y installed (much cutting of headrest metal plate/sponge/plastic speaker cover); would probably have been better to go for something smaller...GTO302s maybe.... For reference - the JBLs have 75mm magnets, a mounting depth of 48mm *AND* a tweeter which sits slightly "proud" of the woofer itself. The bottom line is that if you were to just shove them in and zip it all back up you'd end up with speakers held tightly in place but with serious risk of damage to the tweeter.
In the end I cut:
* crescents out of the centrally located metal plate that runs up the back of each seat (as little metal as possible was removed!);
* foam from the back of the headrest (to allow the magnet/speaker to sit as far back as necessary to avoid pressure on the tweeter);
* foam from the front face of the headrest to allow the speaker surround to fit in a recess;
* the plastic in the headrest "shell" also!
I wasn''t delirious about cutting the metal plate but tweeter damage was inevitable otherwise.
See: http://members.tripod.co.uk/yee_har/roadster/roadster_images/jbl_gto402.jpg for the "before" pic;

http://www.spiceisle.com/audiodiy/projects/cartf/ more on speaker performance really

http://albums.photopoint.com/j/AlbumIndex?u=43457&a=291406 Martyn Brearley, 6.5" pair of kicker rear speakers

http://www.mx-5.de/html/soundboard_fur_den_na.html rear parcel shelf dimensions

http://www.jlaudio.com/stealthbox/miata.html JL Audio stealth box - a bit pricy but sounds great..

http://www.geocities.com/MotorCity/Garage/4991/sound2.html
http://www.mmi.org/haycock/rear.html
http://users.technocraft.com/~dune/miata/sub.html

http://albums.photopoint.com/j/AlbumIndex?u=43457&a=291406
http://albums.photopoint.com/j/AlbumIndex?u=117212&a=1150565
http://albums.photopoint.com/j/AlbumList?u=117212&Auth=false

http://www.mugi.net/moogee/gavphotos.htm boot mounted 10" sub

And then there is Hugo Fiennes MP3 player; http://utter.chaos.org.uk/~altman/mp3mobile

If you hit the site at the top level and look in the "cellular accessories" section there's some more info. They are about 40 quid. http://www.demon.co.uk/buss-srv/jmcomms/access/taxdisc.jpg

Holds 4 cds in a single DIN slot; http://www.seriousauto.com/cdcaddy.html

"First off, why do we need to balance the speaker impedance to the drive capability of the stereo? Several reasons, but the main one is to provide the best tradeoff between power transfer to the speaker while preventing the output stage from saturating. The output stage of the stereo is a transistor drive which modulates the voltage across the speaker according to the sound required. This voltage drives a current through the speaker coil, creating a magnetic field which moves the speaker cone forward and back, producing the air movement that we perceive as sound. There are limits to both the amount of current and the peak voltage that the transistors can supply, which can be derived from the peak power (not the rms power) of the stereo, since power is the product of current and voltage, while Ohm's Law tells us that voltage is the product of power and impedance. Thus power can be derived from either the square of the drive voltage DIVIDED by the impedance, or the square of the drive current MULTIPLIED by the impedance - both are equivalent calculations.

Most car units will drive a maximum 14V (derived from the car battery) across the speakers. With 8Ohm speakers this means that the maximum peak power on each channel is 14x14/8 = 24.5W. That is why most car systems use 4Ohm speakers as standard, as opposed to the 8Ohms in domestic systems. With 4Ohm speakers the maximum peak power on each channel is 14x14/4 = 49W. To provide higher peak power drive, the stereo must contain additional circuits to increase the drive voltage above the supply level available from the battery. (Editor … hence external amplifiers are 50% voltage pump systems by volume .. they drive the voltages up to about 40W to allow 400W outputs)

This is a gross oversimplification of course, because the movement of the speaker coil in the magnetic field generates a reverse voltage (called back EMF) which has the effect of causing the apparent impedance of the speaker to be much higher than it is rated.

In either case however, if the power output of the stereo reaches its limits severe audio distortion will occur. Saturation can occur in several ways, including the drive voltage reaching its limits, the drive current reaching its limits or the speaker coil movement limiting as it nears the edges of the magnetic field. If the impedance presented to the stereo is matched with the design of the unit then the voltage and current saturation should occur at roughly the same point in the power curve. If too low a speaker impedance is used, the current output capacity of the stereo will limit well before the voltage reaches its maximum and vice versa if too high a speaker impedance is used. So, if the wrong impedance is presented to the stereo then the output will severely distort long before the speaker or the stereo maximum capacity is reached.

On the stock radio there are/should be two independent drives, nominally front and rear. The front drives are connected to the two 4 Ohm door speakers (left and right channels), as below:

Front Speakers
RADIO FRONT OUTPUT SPEAKERS
L+________________________________L+ _/|
L-________________________________L- |_ |4Ohm Left Door
\|

R+________________________________R+ _/|
R-________________________________R- |_ |4Ohm Right Door
\|

On the headrest speakers things are a little different, because there are two speakers connected to each channel of the rear drive, one left- right pair for the passenger seat and another pair for the driver seat. These can be wired differently, but as I understand it are normally connected in parallel (so that unplugging one seat doesn't cut the sound to the other seat) as below. The parallel wiring to the 4 separate outputs is normally done in the terminal block itself, which plugs into the rear of the radio, so it might *appear* that there are 4 independent drive connections, even though there are really only 2.

Headrest Speakers
RADIO REAR TERMINAL BLOCK
OUTPUT ADAPTER SPEAKERS
L+__________________,_____________L+ _/|
L-________________,_|_____________L- |_ |8Ohm Left Passenger
| | \|
| |
| |_____________L+ _/|
|_______________L- |_ |8Ohm Left Driver
\|

R+__________________,_____________R+ _/|
R-________________,_|_____________R- |_ |8Ohm Right Passenger
| | \|
| |
| |_____________R+ _/|
|_______________R- |_ |8Ohm Right Driver
\|

This wiring presents the correct 4Ohm load on each channel of the stereo, since impedance in parallel divides by the number of units. However only 1/2 of the power output available on the door speakers appears on each of the headrest speakers, since the current is split equally between the two speakers. This results in approximately half the volume level for equivalent efficiency speakers. Since your ears are so much closer to the headrests than the door speakers this should be well within control of the front/rear balance adjustment on the stereo. However, where this balance adjust normally sits depends heavily on the relative efficiency of the door and headrest speakers. A general rule of thumb is that better quality speakers (ie. Lower audio distortion at equal sound pressure) have lower efficiency and therefore require more drive.

The 'cowboy' solution to this is to replace the headrest speakers with 4Ohm units, presenting a 2Ohm output load to the stereo. While this provides a louder output from each of the headrest speakers, the lower impedance seen by the stereo means that the final drive transistors are working twice as hard to drive them. This can cause distortion, severe at high volumes, as the output current saturates and can even damage the stereo by burning out the final drive stage through overheating as the average current through each transistor doubles.

The correct solution (but more expensive and thus not fitted as standard) is to do exactly what you have done - drive each speaker from an independent amplifier. That way each speaker presents the correct load to the drive and all of the driven power reaches each speaker. This is also a much better way of driving 4 independent speakers in any case because putting two speakers on the same drive is never ideal. Manufacturing tolerances mean that the resonant frequency of each speaker is slightly different so the balance of back EMF between speakers will change with frequency. Consequently the distribution of current between each speaker is not even across the audio spectrum and this causes distortion as well. I would guess that this was the cause of your initial dissatisfaction with the shared 4Ohm drive, rather than the severe distortion referred to above.

The bottom line is that the correct solution to driving the headrest speakers and one that is far superior, both in practice and theory, to the shared drive the stock systems are wired up for - whether used with 4Ohm, 8Ohm or any other speaker impedance." Kennedy rkm@nospam.demon.co.uk

"Most head units quote their power as peak to peak power, which is an instantaneous measurement rather than RMS (root mean squared) which is an average and is therefore rather more meaningful, as it reflects the requirements the amp itself puts on its power supply.

OK, some simple ohms law type stuff

1) Power = Voltage * Current = VI

2) Current (neglecting the fact that a speaker is an inductive, rather than resistive load, and so avoiding the complicated calculus bits) = Voltage divided by resistance = V/R

3) Combine the two and you get P = Vsquared/R.

OK For one channel, R = 4ohms, and V is 12V. (OK, now you see why car applications use 4ohms= gives a higher power drive for the same input voltage)

So we have 144/4 = 36WRMS. Now bearing in mind amps are 80-90% efficient, and actually the load the amp sees from the speaker is higher than 4ohms at 2KHz and above(where most music power is), then you can see why most head units are limited to similar numbers on 40W peak. There is a hard limit imposed by the voltage supplied by the battery. Also these internal amps, in order for them to be small, have poorer output impedance characteristics and linearity translated means poorer sound quality. Its possible to use a device called a DC-DC converter, which can create an output voltage greater than the input (= more power), switching a power MOSFET transistor across and inductor at high frequency but these are bulky and expensive by comparison, and could never fit inside a head unit.

In simple terms, if our cars had 250V AC on tap it would be dead easy to generate a high enough voltage for a meaty power amp." Chris Coleman