Having bought a wind deflector in good condition with built in speakers at a reasonable price from good ol’ $Bay for my NB, it was a case of looking at replacing the speaker units as the originals are reputed to be audibly very tinny (verified by a test connection from the radio). I didn’t want to shoehorn speakers into my existing standard wind deflector as my DIY skills for an aesthetically pleasing conversion aren’t high enough although there are plenty of articles both on this site and on www.miata.net.
I could have opted for buying a plug 'n play kit from Third Millenium in the States, but their relatively high purchase price together with shipping (over $20) and presumably import duty led me to investigate alternatives. Anyway, doing a bit of work, rather than the equivalent of simple Lego assembly is somewhat more intellectually satisfying.
I’m not going to attach photos as Third Millenium’s web site for their offering includes a useful video. See https://www.3rdstrategy.com/M200.html
My choice of speakers came down eventually to a pair of Visaton FRS 7S 2.5" driver units - stock number LS04840 from CPC Farnell ( https://cpc.farnell.com ) for a smidgeon under £20 a pair including free delivery. CPC are very useful as they supply data sheets online on virtually everything they sell.
Fitting was fairly straightforward. The speakers needed their mounting holes extended by about 3mm toward each rounded corner. Should the reader do this, then be sure to wrap the whole of the front and rear of the speaker in masking tape, as metal filings from reaming (I used an ordinary HSS drill bit in my drill on a vertical stand) invariably are attracted to the magnet. With reaming finished, it is a simple task to wrap some more masking tape around the said filings to trap them and then pull the whole lot off from the driver units. The polarity of the speaker terminals are in the same position as on the originals so it is a simple matter of cutting off the existing wiring and re-soldering onto the new units. They don’t need frequency crossover capacitors as did the originals.
The new speakers are fractionally too high for the rear covers so I ground down the plastic mounting posts flush with the inner cylinder behind the front grill and then ground down the cylinder and posts a further 3mm. Grinding was done using a rotary stone in the drill. Be sure to rotate a drill bit into each screw hole to remove the semi-molten plastic immediately after grinding each post before it sets. Then just use the original mounting screws with suitable-sized nuts to act as spacers between the loudspeaker and the self-tapper head to preserve the effective screw depth.
That’s about it. It was straightforward and reasonably quick to do. Is it an improvement over the standard two-speaker system at speed? Definitely so, although this wasn’t the only factor as I fitted a hardtop at the same time, so I can’t say what they are like in a top-down situation. You won’t get any sort of bass from these small units but they reinforce the existing door units pretty well.